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postgresql/src/backend/replication/walsender.c

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/*-------------------------------------------------------------------------
*
* walsender.c
*
* The WAL sender process (walsender) is new as of Postgres 9.0. It takes
* care of sending XLOG from the primary server to a single recipient.
* (Note that there can be more than one walsender process concurrently.)
* It is started by the postmaster when the walreceiver of a standby server
* connects to the primary server and requests XLOG streaming replication.
*
* A walsender is similar to a regular backend, ie. there is a one-to-one
* relationship between a connection and a walsender process, but instead
* of processing SQL queries, it understands a small set of special
* replication-mode commands. The START_REPLICATION command begins streaming
* WAL to the client. While streaming, the walsender keeps reading XLOG
* records from the disk and sends them to the standby server over the
* COPY protocol, until the either side ends the replication by exiting COPY
* mode (or until the connection is closed).
*
* Normal termination is by SIGTERM, which instructs the walsender to
* close the connection and exit(0) at next convenient moment. Emergency
* termination is by SIGQUIT; like any backend, the walsender will simply
* abort and exit on SIGQUIT. A close of the connection and a FATAL error
* are treated as not a crash but approximately normal termination;
* the walsender will exit quickly without sending any more XLOG records.
*
* If the server is shut down, postmaster sends us SIGUSR2 after all
* regular backends have exited and the shutdown checkpoint has been written.
* This instructs walsender to send any outstanding WAL, including the
* shutdown checkpoint record, wait for it to be replicated to the standby,
* and then exit.
*
*
* Portions Copyright (c) 2010-2016, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/backend/replication/walsender.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <signal.h>
#include <unistd.h>
#include "access/timeline.h"
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog_internal.h"
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
#include "funcapi.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "nodes/replnodes.h"
#include "pgstat.h"
#include "replication/basebackup.h"
#include "replication/decode.h"
#include "replication/logical.h"
#include "replication/logicalfuncs.h"
#include "replication/slot.h"
#include "replication/snapbuild.h"
#include "replication/syncrep.h"
#include "replication/walreceiver.h"
#include "replication/walsender.h"
#include "replication/walsender_private.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/pmsignal.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "tcop/tcopprot.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/memutils.h"
#include "utils/pg_lsn.h"
#include "utils/ps_status.h"
#include "utils/resowner.h"
#include "utils/timeout.h"
#include "utils/timestamp.h"
/*
* Maximum data payload in a WAL data message. Must be >= XLOG_BLCKSZ.
*
* We don't have a good idea of what a good value would be; there's some
* overhead per message in both walsender and walreceiver, but on the other
* hand sending large batches makes walsender less responsive to signals
* because signals are checked only between messages. 128kB (with
* default 8k blocks) seems like a reasonable guess for now.
*/
#define MAX_SEND_SIZE (XLOG_BLCKSZ * 16)
/* Array of WalSnds in shared memory */
WalSndCtlData *WalSndCtl = NULL;
/* My slot in the shared memory array */
WalSnd *MyWalSnd = NULL;
/* Global state */
bool am_walsender = false; /* Am I a walsender process? */
bool am_cascading_walsender = false; /* Am I cascading WAL to
* another standby? */
bool am_db_walsender = false; /* Connected to a database? */
/* User-settable parameters for walsender */
int max_wal_senders = 0; /* the maximum number of concurrent walsenders */
int wal_sender_timeout = 60 * 1000; /* maximum time to send one
* WAL data message */
bool log_replication_commands = false;
/*
* State for WalSndWakeupRequest
*/
bool wake_wal_senders = false;
/*
* These variables are used similarly to openLogFile/SegNo/Off,
* but for walsender to read the XLOG.
*/
static int sendFile = -1;
static XLogSegNo sendSegNo = 0;
static uint32 sendOff = 0;
/* Timeline ID of the currently open file */
static TimeLineID curFileTimeLine = 0;
/*
* These variables keep track of the state of the timeline we're currently
* sending. sendTimeLine identifies the timeline. If sendTimeLineIsHistoric,
* the timeline is not the latest timeline on this server, and the server's
* history forked off from that timeline at sendTimeLineValidUpto.
*/
static TimeLineID sendTimeLine = 0;
static TimeLineID sendTimeLineNextTLI = 0;
static bool sendTimeLineIsHistoric = false;
static XLogRecPtr sendTimeLineValidUpto = InvalidXLogRecPtr;
/*
* How far have we sent WAL already? This is also advertised in
* MyWalSnd->sentPtr. (Actually, this is the next WAL location to send.)
*/
static XLogRecPtr sentPtr = 0;
/* Buffers for constructing outgoing messages and processing reply messages. */
static StringInfoData output_message;
static StringInfoData reply_message;
static StringInfoData tmpbuf;
/*
* Timestamp of the last receipt of the reply from the standby. Set to 0 if
* wal_sender_timeout doesn't need to be active.
*/
static TimestampTz last_reply_timestamp = 0;
/* Have we sent a heartbeat message asking for reply, since last reply? */
static bool waiting_for_ping_response = false;
/*
* While streaming WAL in Copy mode, streamingDoneSending is set to true
* after we have sent CopyDone. We should not send any more CopyData messages
* after that. streamingDoneReceiving is set to true when we receive CopyDone
* from the other end. When both become true, it's time to exit Copy mode.
*/
static bool streamingDoneSending;
static bool streamingDoneReceiving;
/* Are we there yet? */
static bool WalSndCaughtUp = false;
/* Flags set by signal handlers for later service in main loop */
static volatile sig_atomic_t got_SIGHUP = false;
static volatile sig_atomic_t walsender_ready_to_stop = false;
/*
* This is set while we are streaming. When not set, SIGUSR2 signal will be
* handled like SIGTERM. When set, the main loop is responsible for checking
* walsender_ready_to_stop and terminating when it's set (after streaming any
* remaining WAL).
*/
static volatile sig_atomic_t replication_active = false;
static LogicalDecodingContext *logical_decoding_ctx = NULL;
static XLogRecPtr logical_startptr = InvalidXLogRecPtr;
/* Signal handlers */
static void WalSndSigHupHandler(SIGNAL_ARGS);
static void WalSndXLogSendHandler(SIGNAL_ARGS);
static void WalSndLastCycleHandler(SIGNAL_ARGS);
/* Prototypes for private functions */
typedef void (*WalSndSendDataCallback) (void);
static void WalSndLoop(WalSndSendDataCallback send_data);
static void InitWalSenderSlot(void);
static void WalSndKill(int code, Datum arg);
static void WalSndShutdown(void) pg_attribute_noreturn();
static void XLogSendPhysical(void);
static void XLogSendLogical(void);
static void WalSndDone(WalSndSendDataCallback send_data);
static XLogRecPtr GetStandbyFlushRecPtr(void);
static void IdentifySystem(void);
static void CreateReplicationSlot(CreateReplicationSlotCmd *cmd);
static void DropReplicationSlot(DropReplicationSlotCmd *cmd);
static void StartReplication(StartReplicationCmd *cmd);
static void StartLogicalReplication(StartReplicationCmd *cmd);
static void ProcessStandbyMessage(void);
static void ProcessStandbyReplyMessage(void);
static void ProcessStandbyHSFeedbackMessage(void);
static void ProcessRepliesIfAny(void);
static void WalSndKeepalive(bool requestReply);
static void WalSndKeepaliveIfNecessary(TimestampTz now);
static void WalSndCheckTimeOut(TimestampTz now);
static long WalSndComputeSleeptime(TimestampTz now);
static void WalSndPrepareWrite(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid, bool last_write);
static void WalSndWriteData(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid, bool last_write);
static XLogRecPtr WalSndWaitForWal(XLogRecPtr loc);
static void XLogRead(char *buf, XLogRecPtr startptr, Size count);
/* Initialize walsender process before entering the main command loop */
void
InitWalSender(void)
{
am_cascading_walsender = RecoveryInProgress();
/* Create a per-walsender data structure in shared memory */
InitWalSenderSlot();
/* Set up resource owner */
CurrentResourceOwner = ResourceOwnerCreate(NULL, "walsender top-level resource owner");
/*
* Let postmaster know that we're a WAL sender. Once we've declared us as
* a WAL sender process, postmaster will let us outlive the bgwriter and
* kill us last in the shutdown sequence, so we get a chance to stream all
* remaining WAL at shutdown, including the shutdown checkpoint. Note that
* there's no going back, and we mustn't write any WAL records after this.
*/
MarkPostmasterChildWalSender();
SendPostmasterSignal(PMSIGNAL_ADVANCE_STATE_MACHINE);
}
/*
* Clean up after an error.
*
* WAL sender processes don't use transactions like regular backends do.
* This function does any cleanup requited after an error in a WAL sender
* process, similar to what transaction abort does in a regular backend.
*/
void
WalSndErrorCleanup(void)
{
LWLockReleaseAll();
pgstat_report_wait_end();
if (sendFile >= 0)
{
close(sendFile);
sendFile = -1;
}
if (MyReplicationSlot != NULL)
ReplicationSlotRelease();
replication_active = false;
if (walsender_ready_to_stop)
proc_exit(0);
/* Revert back to startup state */
WalSndSetState(WALSNDSTATE_STARTUP);
}
/*
* Handle a client's connection abort in an orderly manner.
*/
static void
WalSndShutdown(void)
{
/*
* Reset whereToSendOutput to prevent ereport from attempting to send any
* more messages to the standby.
*/
if (whereToSendOutput == DestRemote)
whereToSendOutput = DestNone;
proc_exit(0);
abort(); /* keep the compiler quiet */
}
/*
* Handle the IDENTIFY_SYSTEM command.
*/
static void
IdentifySystem(void)
{
StringInfoData buf;
char sysid[32];
char tli[11];
char xpos[MAXFNAMELEN];
XLogRecPtr logptr;
char *dbname = NULL;
Size len;
/*
* Reply with a result set with one row, four columns. First col is system
* ID, second is timeline ID, third is current xlog location and the
* fourth contains the database name if we are connected to one.
*/
snprintf(sysid, sizeof(sysid), UINT64_FORMAT,
GetSystemIdentifier());
am_cascading_walsender = RecoveryInProgress();
if (am_cascading_walsender)
{
/* this also updates ThisTimeLineID */
logptr = GetStandbyFlushRecPtr();
}
else
logptr = GetFlushRecPtr();
snprintf(tli, sizeof(tli), "%u", ThisTimeLineID);
snprintf(xpos, sizeof(xpos), "%X/%X", (uint32) (logptr >> 32), (uint32) logptr);
if (MyDatabaseId != InvalidOid)
{
MemoryContext cur = CurrentMemoryContext;
/* syscache access needs a transaction env. */
StartTransactionCommand();
/* make dbname live outside TX context */
MemoryContextSwitchTo(cur);
dbname = get_database_name(MyDatabaseId);
CommitTransactionCommand();
/* CommitTransactionCommand switches to TopMemoryContext */
MemoryContextSwitchTo(cur);
}
/* Send a RowDescription message */
pq_beginmessage(&buf, 'T');
pq_sendint(&buf, 4, 2); /* 4 fields */
/* first field */
pq_sendstring(&buf, "systemid"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
/* second field */
pq_sendstring(&buf, "timeline"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, INT4OID, 4); /* type oid */
pq_sendint(&buf, 4, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
/* third field */
pq_sendstring(&buf, "xlogpos"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
/* fourth field */
pq_sendstring(&buf, "dbname"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
pq_endmessage(&buf);
/* Send a DataRow message */
pq_beginmessage(&buf, 'D');
pq_sendint(&buf, 4, 2); /* # of columns */
/* column 1: system identifier */
len = strlen(sysid);
pq_sendint(&buf, len, 4);
pq_sendbytes(&buf, (char *) &sysid, len);
/* column 2: timeline */
len = strlen(tli);
pq_sendint(&buf, len, 4);
pq_sendbytes(&buf, (char *) tli, len);
/* column 3: xlog position */
len = strlen(xpos);
pq_sendint(&buf, len, 4);
pq_sendbytes(&buf, (char *) xpos, len);
/* column 4: database name, or NULL if none */
if (dbname)
{
len = strlen(dbname);
pq_sendint(&buf, len, 4);
pq_sendbytes(&buf, (char *) dbname, len);
}
else
{
pq_sendint(&buf, -1, 4);
}
pq_endmessage(&buf);
}
/*
* Handle TIMELINE_HISTORY command.
*/
static void
SendTimeLineHistory(TimeLineHistoryCmd *cmd)
{
StringInfoData buf;
char histfname[MAXFNAMELEN];
char path[MAXPGPATH];
int fd;
off_t histfilelen;
off_t bytesleft;
Size len;
/*
* Reply with a result set with one row, and two columns. The first col is
* the name of the history file, 2nd is the contents.
*/
TLHistoryFileName(histfname, cmd->timeline);
TLHistoryFilePath(path, cmd->timeline);
/* Send a RowDescription message */
pq_beginmessage(&buf, 'T');
pq_sendint(&buf, 2, 2); /* 2 fields */
/* first field */
pq_sendstring(&buf, "filename"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
/* second field */
pq_sendstring(&buf, "content"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, BYTEAOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
pq_endmessage(&buf);
/* Send a DataRow message */
pq_beginmessage(&buf, 'D');
pq_sendint(&buf, 2, 2); /* # of columns */
len = strlen(histfname);
pq_sendint(&buf, len, 4); /* col1 len */
pq_sendbytes(&buf, histfname, len);
fd = OpenTransientFile(path, O_RDONLY | PG_BINARY, 0666);
if (fd < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open file \"%s\": %m", path)));
/* Determine file length and send it to client */
histfilelen = lseek(fd, 0, SEEK_END);
if (histfilelen < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek to end of file \"%s\": %m", path)));
if (lseek(fd, 0, SEEK_SET) != 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek to beginning of file \"%s\": %m", path)));
pq_sendint(&buf, histfilelen, 4); /* col2 len */
bytesleft = histfilelen;
while (bytesleft > 0)
{
char rbuf[BLCKSZ];
int nread;
nread = read(fd, rbuf, sizeof(rbuf));
if (nread <= 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read file \"%s\": %m",
path)));
pq_sendbytes(&buf, rbuf, nread);
bytesleft -= nread;
}
CloseTransientFile(fd);
pq_endmessage(&buf);
}
/*
* Handle START_REPLICATION command.
*
* At the moment, this never returns, but an ereport(ERROR) will take us back
* to the main loop.
*/
static void
StartReplication(StartReplicationCmd *cmd)
{
StringInfoData buf;
XLogRecPtr FlushPtr;
/*
* We assume here that we're logging enough information in the WAL for
* log-shipping, since this is checked in PostmasterMain().
*
* NOTE: wal_level can only change at shutdown, so in most cases it is
* difficult for there to be WAL data that we can still see that was
* written at wal_level='minimal'.
*/
if (cmd->slotname)
{
ReplicationSlotAcquire(cmd->slotname);
if (SlotIsLogical(MyReplicationSlot))
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
(errmsg("cannot use a logical replication slot for physical replication"))));
}
/*
* Select the timeline. If it was given explicitly by the client, use
* that. Otherwise use the timeline of the last replayed record, which is
* kept in ThisTimeLineID.
*/
if (am_cascading_walsender)
{
/* this also updates ThisTimeLineID */
FlushPtr = GetStandbyFlushRecPtr();
}
else
FlushPtr = GetFlushRecPtr();
if (cmd->timeline != 0)
{
XLogRecPtr switchpoint;
sendTimeLine = cmd->timeline;
if (sendTimeLine == ThisTimeLineID)
{
sendTimeLineIsHistoric = false;
sendTimeLineValidUpto = InvalidXLogRecPtr;
}
else
{
List *timeLineHistory;
sendTimeLineIsHistoric = true;
/*
* Check that the timeline the client requested for exists, and
* the requested start location is on that timeline.
*/
timeLineHistory = readTimeLineHistory(ThisTimeLineID);
switchpoint = tliSwitchPoint(cmd->timeline, timeLineHistory,
&sendTimeLineNextTLI);
list_free_deep(timeLineHistory);
/*
* Found the requested timeline in the history. Check that
* requested startpoint is on that timeline in our history.
*
* This is quite loose on purpose. We only check that we didn't
* fork off the requested timeline before the switchpoint. We
* don't check that we switched *to* it before the requested
* starting point. This is because the client can legitimately
* request to start replication from the beginning of the WAL
* segment that contains switchpoint, but on the new timeline, so
* that it doesn't end up with a partial segment. If you ask for a
* too old starting point, you'll get an error later when we fail
* to find the requested WAL segment in pg_xlog.
*
* XXX: we could be more strict here and only allow a startpoint
* that's older than the switchpoint, if it's still in the same
* WAL segment.
*/
if (!XLogRecPtrIsInvalid(switchpoint) &&
switchpoint < cmd->startpoint)
{
ereport(ERROR,
(errmsg("requested starting point %X/%X on timeline %u is not in this server's history",
(uint32) (cmd->startpoint >> 32),
(uint32) (cmd->startpoint),
cmd->timeline),
errdetail("This server's history forked from timeline %u at %X/%X.",
cmd->timeline,
(uint32) (switchpoint >> 32),
(uint32) (switchpoint))));
}
sendTimeLineValidUpto = switchpoint;
}
}
else
{
sendTimeLine = ThisTimeLineID;
sendTimeLineValidUpto = InvalidXLogRecPtr;
sendTimeLineIsHistoric = false;
}
streamingDoneSending = streamingDoneReceiving = false;
/* If there is nothing to stream, don't even enter COPY mode */
if (!sendTimeLineIsHistoric || cmd->startpoint < sendTimeLineValidUpto)
{
/*
* When we first start replication the standby will be behind the
* primary. For some applications, for example, synchronous
* replication, it is important to have a clear state for this initial
* catchup mode, so we can trigger actions when we change streaming
* state later. We may stay in this state for a long time, which is
* exactly why we want to be able to monitor whether or not we are
* still here.
*/
WalSndSetState(WALSNDSTATE_CATCHUP);
/* Send a CopyBothResponse message, and start streaming */
pq_beginmessage(&buf, 'W');
pq_sendbyte(&buf, 0);
pq_sendint(&buf, 0, 2);
pq_endmessage(&buf);
pq_flush();
/*
* Don't allow a request to stream from a future point in WAL that
* hasn't been flushed to disk in this server yet.
*/
if (FlushPtr < cmd->startpoint)
{
ereport(ERROR,
(errmsg("requested starting point %X/%X is ahead of the WAL flush position of this server %X/%X",
(uint32) (cmd->startpoint >> 32),
(uint32) (cmd->startpoint),
(uint32) (FlushPtr >> 32),
(uint32) (FlushPtr))));
}
/* Start streaming from the requested point */
sentPtr = cmd->startpoint;
/* Initialize shared memory status, too */
{
WalSnd *walsnd = MyWalSnd;
SpinLockAcquire(&walsnd->mutex);
walsnd->sentPtr = sentPtr;
SpinLockRelease(&walsnd->mutex);
}
SyncRepInitConfig();
/* Main loop of walsender */
replication_active = true;
WalSndLoop(XLogSendPhysical);
replication_active = false;
if (walsender_ready_to_stop)
proc_exit(0);
WalSndSetState(WALSNDSTATE_STARTUP);
Assert(streamingDoneSending && streamingDoneReceiving);
}
if (cmd->slotname)
ReplicationSlotRelease();
/*
* Copy is finished now. Send a single-row result set indicating the next
* timeline.
*/
if (sendTimeLineIsHistoric)
{
char tli_str[11];
char startpos_str[8 + 1 + 8 + 1];
Size len;
snprintf(tli_str, sizeof(tli_str), "%u", sendTimeLineNextTLI);
snprintf(startpos_str, sizeof(startpos_str), "%X/%X",
(uint32) (sendTimeLineValidUpto >> 32),
(uint32) sendTimeLineValidUpto);
pq_beginmessage(&buf, 'T'); /* RowDescription */
pq_sendint(&buf, 2, 2); /* 2 fields */
/* Field header */
pq_sendstring(&buf, "next_tli");
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
/*
* int8 may seem like a surprising data type for this, but in theory
* int4 would not be wide enough for this, as TimeLineID is unsigned.
*/
pq_sendint(&buf, INT8OID, 4); /* type oid */
pq_sendint(&buf, -1, 2);
pq_sendint(&buf, 0, 4);
pq_sendint(&buf, 0, 2);
pq_sendstring(&buf, "next_tli_startpos");
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2);
pq_sendint(&buf, 0, 4);
pq_sendint(&buf, 0, 2);
pq_endmessage(&buf);
/* Data row */
pq_beginmessage(&buf, 'D');
pq_sendint(&buf, 2, 2); /* number of columns */
len = strlen(tli_str);
pq_sendint(&buf, len, 4); /* length */
pq_sendbytes(&buf, tli_str, len);
len = strlen(startpos_str);
pq_sendint(&buf, len, 4); /* length */
pq_sendbytes(&buf, startpos_str, len);
pq_endmessage(&buf);
}
/* Send CommandComplete message */
pq_puttextmessage('C', "START_STREAMING");
}
/*
* read_page callback for logical decoding contexts, as a walsender process.
*
* Inside the walsender we can do better than logical_read_local_xlog_page,
* which has to do a plain sleep/busy loop, because the walsender's latch gets
* set every time WAL is flushed.
*/
static int
logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen,
XLogRecPtr targetRecPtr, char *cur_page, TimeLineID *pageTLI)
{
XLogRecPtr flushptr;
int count;
/* make sure we have enough WAL available */
flushptr = WalSndWaitForWal(targetPagePtr + reqLen);
/* more than one block available */
if (targetPagePtr + XLOG_BLCKSZ <= flushptr)
count = XLOG_BLCKSZ;
/* not enough WAL synced, that can happen during shutdown */
else if (targetPagePtr + reqLen > flushptr)
return -1;
/* part of the page available */
else
count = flushptr - targetPagePtr;
/* now actually read the data, we know it's there */
XLogRead(cur_page, targetPagePtr, XLOG_BLCKSZ);
return count;
}
/*
* Create a new replication slot.
*/
static void
CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
{
const char *snapshot_name = NULL;
char xpos[MAXFNAMELEN];
StringInfoData buf;
Size len;
Assert(!MyReplicationSlot);
/* setup state for XLogReadPage */
sendTimeLineIsHistoric = false;
sendTimeLine = ThisTimeLineID;
if (cmd->kind == REPLICATION_KIND_PHYSICAL)
{
ReplicationSlotCreate(cmd->slotname, false, RS_PERSISTENT);
}
else
{
CheckLogicalDecodingRequirements();
/*
* Initially create the slot as ephemeral - that allows us to nicely
* handle errors during initialization because it'll get dropped if
* this transaction fails. We'll make it persistent at the end.
*/
ReplicationSlotCreate(cmd->slotname, true, RS_EPHEMERAL);
}
initStringInfo(&output_message);
if (cmd->kind == REPLICATION_KIND_LOGICAL)
{
LogicalDecodingContext *ctx;
ctx = CreateInitDecodingContext(cmd->plugin, NIL,
logical_read_xlog_page,
WalSndPrepareWrite, WalSndWriteData);
/*
* Signal that we don't need the timeout mechanism. We're just
* creating the replication slot and don't yet accept feedback
* messages or send keepalives. As we possibly need to wait for
* further WAL the walsender would otherwise possibly be killed too
* soon.
*/
last_reply_timestamp = 0;
/* build initial snapshot, might take a while */
DecodingContextFindStartpoint(ctx);
/*
* Export a plain (not of the snapbuild.c type) snapshot to the user
* that can be imported into another session.
*/
snapshot_name = SnapBuildExportSnapshot(ctx->snapshot_builder);
/* don't need the decoding context anymore */
FreeDecodingContext(ctx);
ReplicationSlotPersist();
}
else if (cmd->kind == REPLICATION_KIND_PHYSICAL && cmd->reserve_wal)
{
ReplicationSlotReserveWal();
/* Write this slot to disk */
ReplicationSlotMarkDirty();
ReplicationSlotSave();
}
snprintf(xpos, sizeof(xpos), "%X/%X",
(uint32) (MyReplicationSlot->data.confirmed_flush >> 32),
(uint32) MyReplicationSlot->data.confirmed_flush);
pq_beginmessage(&buf, 'T');
pq_sendint(&buf, 4, 2); /* 4 fields */
/* first field: slot name */
pq_sendstring(&buf, "slot_name"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
/* second field: LSN at which we became consistent */
pq_sendstring(&buf, "consistent_point"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
/* third field: exported snapshot's name */
pq_sendstring(&buf, "snapshot_name"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
/* fourth field: output plugin */
pq_sendstring(&buf, "output_plugin"); /* col name */
pq_sendint(&buf, 0, 4); /* table oid */
pq_sendint(&buf, 0, 2); /* attnum */
pq_sendint(&buf, TEXTOID, 4); /* type oid */
pq_sendint(&buf, -1, 2); /* typlen */
pq_sendint(&buf, 0, 4); /* typmod */
pq_sendint(&buf, 0, 2); /* format code */
pq_endmessage(&buf);
/* Send a DataRow message */
pq_beginmessage(&buf, 'D');
pq_sendint(&buf, 4, 2); /* # of columns */
/* slot_name */
len = strlen(NameStr(MyReplicationSlot->data.name));
pq_sendint(&buf, len, 4); /* col1 len */
pq_sendbytes(&buf, NameStr(MyReplicationSlot->data.name), len);
/* consistent wal location */
len = strlen(xpos);
pq_sendint(&buf, len, 4);
pq_sendbytes(&buf, xpos, len);
/* snapshot name, or NULL if none */
if (snapshot_name != NULL)
{
len = strlen(snapshot_name);
pq_sendint(&buf, len, 4);
pq_sendbytes(&buf, snapshot_name, len);
}
else
pq_sendint(&buf, -1, 4);
/* plugin, or NULL if none */
if (cmd->plugin != NULL)
{
len = strlen(cmd->plugin);
pq_sendint(&buf, len, 4);
pq_sendbytes(&buf, cmd->plugin, len);
}
else
pq_sendint(&buf, -1, 4);
pq_endmessage(&buf);
/*
* release active status again, START_REPLICATION will reacquire it
*/
ReplicationSlotRelease();
}
/*
* Get rid of a replication slot that is no longer wanted.
*/
static void
DropReplicationSlot(DropReplicationSlotCmd *cmd)
{
ReplicationSlotDrop(cmd->slotname);
EndCommand("DROP_REPLICATION_SLOT", DestRemote);
}
/*
* Load previously initiated logical slot and prepare for sending data (via
* WalSndLoop).
*/
static void
StartLogicalReplication(StartReplicationCmd *cmd)
{
StringInfoData buf;
/* make sure that our requirements are still fulfilled */
CheckLogicalDecodingRequirements();
Assert(!MyReplicationSlot);
ReplicationSlotAcquire(cmd->slotname);
/*
* Force a disconnect, so that the decoding code doesn't need to care
* about an eventual switch from running in recovery, to running in a
* normal environment. Client code is expected to handle reconnects.
*/
if (am_cascading_walsender && !RecoveryInProgress())
{
ereport(LOG,
(errmsg("terminating walsender process after promotion")));
walsender_ready_to_stop = true;
}
WalSndSetState(WALSNDSTATE_CATCHUP);
/* Send a CopyBothResponse message, and start streaming */
pq_beginmessage(&buf, 'W');
pq_sendbyte(&buf, 0);
pq_sendint(&buf, 0, 2);
pq_endmessage(&buf);
pq_flush();
/* setup state for XLogReadPage */
sendTimeLineIsHistoric = false;
sendTimeLine = ThisTimeLineID;
/*
* Initialize position to the last ack'ed one, then the xlog records begin
* to be shipped from that position.
*/
logical_decoding_ctx = CreateDecodingContext(
cmd->startpoint, cmd->options,
logical_read_xlog_page,
WalSndPrepareWrite, WalSndWriteData);
/* Start reading WAL from the oldest required WAL. */
logical_startptr = MyReplicationSlot->data.restart_lsn;
/*
* Report the location after which we'll send out further commits as the
* current sentPtr.
*/
sentPtr = MyReplicationSlot->data.confirmed_flush;
/* Also update the sent position status in shared memory */
{
WalSnd *walsnd = MyWalSnd;
SpinLockAcquire(&walsnd->mutex);
walsnd->sentPtr = MyReplicationSlot->data.restart_lsn;
SpinLockRelease(&walsnd->mutex);
}
replication_active = true;
SyncRepInitConfig();
/* Main loop of walsender */
WalSndLoop(XLogSendLogical);
FreeDecodingContext(logical_decoding_ctx);
ReplicationSlotRelease();
replication_active = false;
if (walsender_ready_to_stop)
proc_exit(0);
WalSndSetState(WALSNDSTATE_STARTUP);
/* Get out of COPY mode (CommandComplete). */
EndCommand("COPY 0", DestRemote);
}
/*
* LogicalDecodingContext 'prepare_write' callback.
*
* Prepare a write into a StringInfo.
*
* Don't do anything lasting in here, it's quite possible that nothing will done
* with the data.
*/
static void
WalSndPrepareWrite(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid, bool last_write)
{
/* can't have sync rep confused by sending the same LSN several times */
if (!last_write)
lsn = InvalidXLogRecPtr;
resetStringInfo(ctx->out);
pq_sendbyte(ctx->out, 'w');
pq_sendint64(ctx->out, lsn); /* dataStart */
pq_sendint64(ctx->out, lsn); /* walEnd */
/*
* Fill out the sendtime later, just as it's done in XLogSendPhysical, but
* reserve space here.
*/
pq_sendint64(ctx->out, 0); /* sendtime */
}
/*
* LogicalDecodingContext 'write' callback.
*
* Actually write out data previously prepared by WalSndPrepareWrite out to
* the network. Take as long as needed, but process replies from the other
* side and check timeouts during that.
*/
static void
WalSndWriteData(LogicalDecodingContext *ctx, XLogRecPtr lsn, TransactionId xid,
bool last_write)
{
/* output previously gathered data in a CopyData packet */
pq_putmessage_noblock('d', ctx->out->data, ctx->out->len);
/*
* Fill the send timestamp last, so that it is taken as late as possible.
* This is somewhat ugly, but the protocol's set as it's already used for
* several releases by streaming physical replication.
*/
resetStringInfo(&tmpbuf);
pq_sendint64(&tmpbuf, GetCurrentIntegerTimestamp());
memcpy(&ctx->out->data[1 + sizeof(int64) + sizeof(int64)],
tmpbuf.data, sizeof(int64));
/* fast path */
/* Try to flush pending output to the client */
if (pq_flush_if_writable() != 0)
WalSndShutdown();
if (!pq_is_send_pending())
return;
for (;;)
{
int wakeEvents;
long sleeptime;
TimestampTz now;
/*
* Emergency bailout if postmaster has died. This is to avoid the
* necessity for manual cleanup of all postmaster children.
*/
if (!PostmasterIsAlive())
exit(1);
/* Clear any already-pending wakeups */
ResetLatch(MyLatch);
CHECK_FOR_INTERRUPTS();
/* Process any requests or signals received recently */
if (got_SIGHUP)
{
got_SIGHUP = false;
ProcessConfigFile(PGC_SIGHUP);
SyncRepInitConfig();
}
/* Check for input from the client */
ProcessRepliesIfAny();
/* Try to flush pending output to the client */
if (pq_flush_if_writable() != 0)
WalSndShutdown();
/* If we finished clearing the buffered data, we're done here. */
if (!pq_is_send_pending())
break;
now = GetCurrentTimestamp();
/* die if timeout was reached */
WalSndCheckTimeOut(now);
/* Send keepalive if the time has come */
WalSndKeepaliveIfNecessary(now);
sleeptime = WalSndComputeSleeptime(now);
wakeEvents = WL_LATCH_SET | WL_POSTMASTER_DEATH |
WL_SOCKET_WRITEABLE | WL_SOCKET_READABLE | WL_TIMEOUT;
/* Sleep until something happens or we time out */
WaitLatchOrSocket(MyLatch, wakeEvents,
MyProcPort->sock, sleeptime);
}
/* reactivate latch so WalSndLoop knows to continue */
SetLatch(MyLatch);
}
/*
* Wait till WAL < loc is flushed to disk so it can be safely read.
*/
static XLogRecPtr
WalSndWaitForWal(XLogRecPtr loc)
{
int wakeEvents;
static XLogRecPtr RecentFlushPtr = InvalidXLogRecPtr;
/*
* Fast path to avoid acquiring the spinlock in the we already know we
* have enough WAL available. This is particularly interesting if we're
* far behind.
*/
if (RecentFlushPtr != InvalidXLogRecPtr &&
loc <= RecentFlushPtr)
return RecentFlushPtr;
/* Get a more recent flush pointer. */
if (!RecoveryInProgress())
RecentFlushPtr = GetFlushRecPtr();
else
RecentFlushPtr = GetXLogReplayRecPtr(NULL);
for (;;)
{
long sleeptime;
TimestampTz now;
/*
* Emergency bailout if postmaster has died. This is to avoid the
* necessity for manual cleanup of all postmaster children.
*/
if (!PostmasterIsAlive())
exit(1);
/* Clear any already-pending wakeups */
ResetLatch(MyLatch);
CHECK_FOR_INTERRUPTS();
/* Process any requests or signals received recently */
if (got_SIGHUP)
{
got_SIGHUP = false;
ProcessConfigFile(PGC_SIGHUP);
SyncRepInitConfig();
}
/* Check for input from the client */
ProcessRepliesIfAny();
/* Update our idea of the currently flushed position. */
if (!RecoveryInProgress())
RecentFlushPtr = GetFlushRecPtr();
else
RecentFlushPtr = GetXLogReplayRecPtr(NULL);
/*
* If postmaster asked us to stop, don't wait here anymore. This will
* cause the xlogreader to return without reading a full record, which
* is the fastest way to reach the mainloop which then can quit.
*
* It's important to do this check after the recomputation of
* RecentFlushPtr, so we can send all remaining data before shutting
* down.
*/
if (walsender_ready_to_stop)
break;
/*
* We only send regular messages to the client for full decoded
* transactions, but a synchronous replication and walsender shutdown
* possibly are waiting for a later location. So we send pings
* containing the flush location every now and then.
*/
if (MyWalSnd->flush < sentPtr &&
MyWalSnd->write < sentPtr &&
!waiting_for_ping_response)
{
WalSndKeepalive(false);
waiting_for_ping_response = true;
}
/* check whether we're done */
if (loc <= RecentFlushPtr)
break;
/* Waiting for new WAL. Since we need to wait, we're now caught up. */
WalSndCaughtUp = true;
/*
* Try to flush pending output to the client. Also wait for the socket
* becoming writable, if there's still pending output after an attempt
* to flush. Otherwise we might just sit on output data while waiting
* for new WAL being generated.
*/
if (pq_flush_if_writable() != 0)
WalSndShutdown();
now = GetCurrentTimestamp();
/* die if timeout was reached */
WalSndCheckTimeOut(now);
/* Send keepalive if the time has come */
WalSndKeepaliveIfNecessary(now);
sleeptime = WalSndComputeSleeptime(now);
wakeEvents = WL_LATCH_SET | WL_POSTMASTER_DEATH |
WL_SOCKET_READABLE | WL_TIMEOUT;
if (pq_is_send_pending())
wakeEvents |= WL_SOCKET_WRITEABLE;
/* Sleep until something happens or we time out */
WaitLatchOrSocket(MyLatch, wakeEvents,
MyProcPort->sock, sleeptime);
}
/* reactivate latch so WalSndLoop knows to continue */
SetLatch(MyLatch);
return RecentFlushPtr;
}
/*
* Execute an incoming replication command.
*/
void
exec_replication_command(const char *cmd_string)
{
int parse_rc;
Node *cmd_node;
MemoryContext cmd_context;
MemoryContext old_context;
/*
* Log replication command if log_replication_commands is enabled. Even
* when it's disabled, log the command with DEBUG1 level for backward
* compatibility.
*/
ereport(log_replication_commands ? LOG : DEBUG1,
(errmsg("received replication command: %s", cmd_string)));
/*
* CREATE_REPLICATION_SLOT ... LOGICAL exports a snapshot until the next
* command arrives. Clean up the old stuff if there's anything.
*/
SnapBuildClearExportedSnapshot();
CHECK_FOR_INTERRUPTS();
cmd_context = AllocSetContextCreate(CurrentMemoryContext,
"Replication command context",
ALLOCSET_DEFAULT_SIZES);
old_context = MemoryContextSwitchTo(cmd_context);
replication_scanner_init(cmd_string);
parse_rc = replication_yyparse();
if (parse_rc != 0)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
(errmsg_internal("replication command parser returned %d",
parse_rc))));
cmd_node = replication_parse_result;
switch (cmd_node->type)
{
case T_IdentifySystemCmd:
IdentifySystem();
break;
case T_BaseBackupCmd:
SendBaseBackup((BaseBackupCmd *) cmd_node);
break;
case T_CreateReplicationSlotCmd:
CreateReplicationSlot((CreateReplicationSlotCmd *) cmd_node);
break;
case T_DropReplicationSlotCmd:
DropReplicationSlot((DropReplicationSlotCmd *) cmd_node);
break;
case T_StartReplicationCmd:
{
StartReplicationCmd *cmd = (StartReplicationCmd *) cmd_node;
if (cmd->kind == REPLICATION_KIND_PHYSICAL)
StartReplication(cmd);
else
StartLogicalReplication(cmd);
break;
}
case T_TimeLineHistoryCmd:
SendTimeLineHistory((TimeLineHistoryCmd *) cmd_node);
break;
default:
elog(ERROR, "unrecognized replication command node tag: %u",
cmd_node->type);
}
/* done */
MemoryContextSwitchTo(old_context);
MemoryContextDelete(cmd_context);
/* Send CommandComplete message */
EndCommand("SELECT", DestRemote);
}
/*
* Process any incoming messages while streaming. Also checks if the remote
* end has closed the connection.
*/
static void
ProcessRepliesIfAny(void)
{
unsigned char firstchar;
int r;
bool received = false;
for (;;)
{
pq_startmsgread();
r = pq_getbyte_if_available(&firstchar);
if (r < 0)
{
/* unexpected error or EOF */
ereport(COMMERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("unexpected EOF on standby connection")));
proc_exit(0);
}
if (r == 0)
{
/* no data available without blocking */
pq_endmsgread();
break;
}
/* Read the message contents */
resetStringInfo(&reply_message);
if (pq_getmessage(&reply_message, 0))
{
ereport(COMMERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("unexpected EOF on standby connection")));
proc_exit(0);
}
/*
* If we already received a CopyDone from the frontend, the frontend
* should not send us anything until we've closed our end of the COPY.
* XXX: In theory, the frontend could already send the next command
* before receiving the CopyDone, but libpq doesn't currently allow
* that.
*/
if (streamingDoneReceiving && firstchar != 'X')
ereport(FATAL,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("unexpected standby message type \"%c\", after receiving CopyDone",
firstchar)));
/* Handle the very limited subset of commands expected in this phase */
switch (firstchar)
{
/*
* 'd' means a standby reply wrapped in a CopyData packet.
*/
case 'd':
ProcessStandbyMessage();
received = true;
break;
/*
* CopyDone means the standby requested to finish streaming.
* Reply with CopyDone, if we had not sent that already.
*/
case 'c':
if (!streamingDoneSending)
{
pq_putmessage_noblock('c', NULL, 0);
streamingDoneSending = true;
}
streamingDoneReceiving = true;
received = true;
break;
/*
* 'X' means that the standby is closing down the socket.
*/
case 'X':
proc_exit(0);
default:
ereport(FATAL,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("invalid standby message type \"%c\"",
firstchar)));
}
}
/*
* Save the last reply timestamp if we've received at least one reply.
*/
if (received)
{
last_reply_timestamp = GetCurrentTimestamp();
waiting_for_ping_response = false;
}
}
/*
* Process a status update message received from standby.
*/
static void
ProcessStandbyMessage(void)
{
char msgtype;
/*
* Check message type from the first byte.
*/
msgtype = pq_getmsgbyte(&reply_message);
switch (msgtype)
{
case 'r':
ProcessStandbyReplyMessage();
break;
case 'h':
ProcessStandbyHSFeedbackMessage();
break;
default:
ereport(COMMERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("unexpected message type \"%c\"", msgtype)));
proc_exit(0);
}
}
/*
* Remember that a walreceiver just confirmed receipt of lsn `lsn`.
*/
static void
PhysicalConfirmReceivedLocation(XLogRecPtr lsn)
{
bool changed = false;
ReplicationSlot *slot = MyReplicationSlot;
Assert(lsn != InvalidXLogRecPtr);
SpinLockAcquire(&slot->mutex);
if (slot->data.restart_lsn != lsn)
{
changed = true;
slot->data.restart_lsn = lsn;
}
SpinLockRelease(&slot->mutex);
if (changed)
{
ReplicationSlotMarkDirty();
ReplicationSlotsComputeRequiredLSN();
}
/*
* One could argue that the slot should be saved to disk now, but that'd
* be energy wasted - the worst lost information can do here is give us
* wrong information in a statistics view - we'll just potentially be more
* conservative in removing files.
*/
}
/*
* Regular reply from standby advising of WAL positions on standby server.
*/
static void
ProcessStandbyReplyMessage(void)
{
XLogRecPtr writePtr,
flushPtr,
applyPtr;
bool replyRequested;
/* the caller already consumed the msgtype byte */
writePtr = pq_getmsgint64(&reply_message);
flushPtr = pq_getmsgint64(&reply_message);
applyPtr = pq_getmsgint64(&reply_message);
(void) pq_getmsgint64(&reply_message); /* sendTime; not used ATM */
replyRequested = pq_getmsgbyte(&reply_message);
elog(DEBUG2, "write %X/%X flush %X/%X apply %X/%X%s",
(uint32) (writePtr >> 32), (uint32) writePtr,
(uint32) (flushPtr >> 32), (uint32) flushPtr,
(uint32) (applyPtr >> 32), (uint32) applyPtr,
replyRequested ? " (reply requested)" : "");
/* Send a reply if the standby requested one. */
if (replyRequested)
WalSndKeepalive(false);
/*
* Update shared state for this WalSender process based on reply data from
* standby.
*/
{
WalSnd *walsnd = MyWalSnd;
SpinLockAcquire(&walsnd->mutex);
walsnd->write = writePtr;
walsnd->flush = flushPtr;
walsnd->apply = applyPtr;
SpinLockRelease(&walsnd->mutex);
}
if (!am_cascading_walsender)
SyncRepReleaseWaiters();
/*
* Advance our local xmin horizon when the client confirmed a flush.
*/
if (MyReplicationSlot && flushPtr != InvalidXLogRecPtr)
{
if (SlotIsLogical(MyReplicationSlot))
LogicalConfirmReceivedLocation(flushPtr);
else
PhysicalConfirmReceivedLocation(flushPtr);
}
}
/* compute new replication slot xmin horizon if needed */
static void
PhysicalReplicationSlotNewXmin(TransactionId feedbackXmin)
{
bool changed = false;
ReplicationSlot *slot = MyReplicationSlot;
SpinLockAcquire(&slot->mutex);
MyPgXact->xmin = InvalidTransactionId;
/*
* For physical replication we don't need the interlock provided by xmin
* and effective_xmin since the consequences of a missed increase are
* limited to query cancellations, so set both at once.
*/
if (!TransactionIdIsNormal(slot->data.xmin) ||
!TransactionIdIsNormal(feedbackXmin) ||
TransactionIdPrecedes(slot->data.xmin, feedbackXmin))
{
changed = true;
slot->data.xmin = feedbackXmin;
slot->effective_xmin = feedbackXmin;
}
SpinLockRelease(&slot->mutex);
if (changed)
{
ReplicationSlotMarkDirty();
ReplicationSlotsComputeRequiredXmin(false);
}
}
/*
* Hot Standby feedback
*/
static void
ProcessStandbyHSFeedbackMessage(void)
{
TransactionId nextXid;
uint32 nextEpoch;
TransactionId feedbackXmin;
uint32 feedbackEpoch;
/*
* Decipher the reply message. The caller already consumed the msgtype
* byte.
*/
(void) pq_getmsgint64(&reply_message); /* sendTime; not used ATM */
feedbackXmin = pq_getmsgint(&reply_message, 4);
feedbackEpoch = pq_getmsgint(&reply_message, 4);
elog(DEBUG2, "hot standby feedback xmin %u epoch %u",
feedbackXmin,
feedbackEpoch);
/* Unset WalSender's xmin if the feedback message value is invalid */
if (!TransactionIdIsNormal(feedbackXmin))
{
MyPgXact->xmin = InvalidTransactionId;
if (MyReplicationSlot != NULL)
PhysicalReplicationSlotNewXmin(feedbackXmin);
return;
}
/*
* Check that the provided xmin/epoch are sane, that is, not in the future
* and not so far back as to be already wrapped around. Ignore if not.
*
* Epoch of nextXid should be same as standby, or if the counter has
* wrapped, then one greater than standby.
*/
GetNextXidAndEpoch(&nextXid, &nextEpoch);
if (feedbackXmin <= nextXid)
{
if (feedbackEpoch != nextEpoch)
return;
}
else
{
if (feedbackEpoch + 1 != nextEpoch)
return;
}
if (!TransactionIdPrecedesOrEquals(feedbackXmin, nextXid))
return; /* epoch OK, but it's wrapped around */
/*
* Set the WalSender's xmin equal to the standby's requested xmin, so that
* the xmin will be taken into account by GetOldestXmin. This will hold
* back the removal of dead rows and thereby prevent the generation of
* cleanup conflicts on the standby server.
*
* There is a small window for a race condition here: although we just
* checked that feedbackXmin precedes nextXid, the nextXid could have
* gotten advanced between our fetching it and applying the xmin below,
* perhaps far enough to make feedbackXmin wrap around. In that case the
* xmin we set here would be "in the future" and have no effect. No point
* in worrying about this since it's too late to save the desired data
* anyway. Assuming that the standby sends us an increasing sequence of
* xmins, this could only happen during the first reply cycle, else our
* own xmin would prevent nextXid from advancing so far.
*
* We don't bother taking the ProcArrayLock here. Setting the xmin field
* is assumed atomic, and there's no real need to prevent a concurrent
* GetOldestXmin. (If we're moving our xmin forward, this is obviously
* safe, and if we're moving it backwards, well, the data is at risk
* already since a VACUUM could have just finished calling GetOldestXmin.)
*
* If we're using a replication slot we reserve the xmin via that,
* otherwise via the walsender's PGXACT entry.
*
* XXX: It might make sense to generalize the ephemeral slot concept and
* always use the slot mechanism to handle the feedback xmin.
*/
if (MyReplicationSlot != NULL) /* XXX: persistency configurable? */
PhysicalReplicationSlotNewXmin(feedbackXmin);
else
MyPgXact->xmin = feedbackXmin;
}
/*
* Compute how long send/receive loops should sleep.
*
* If wal_sender_timeout is enabled we want to wake up in time to send
* keepalives and to abort the connection if wal_sender_timeout has been
* reached.
*/
static long
WalSndComputeSleeptime(TimestampTz now)
{
long sleeptime = 10000; /* 10 s */
if (wal_sender_timeout > 0 && last_reply_timestamp > 0)
{
TimestampTz wakeup_time;
long sec_to_timeout;
int microsec_to_timeout;
/*
* At the latest stop sleeping once wal_sender_timeout has been
* reached.
*/
wakeup_time = TimestampTzPlusMilliseconds(last_reply_timestamp,
wal_sender_timeout);
/*
* If no ping has been sent yet, wakeup when it's time to do so.
* WalSndKeepaliveIfNecessary() wants to send a keepalive once half of
* the timeout passed without a response.
*/
if (!waiting_for_ping_response)
wakeup_time = TimestampTzPlusMilliseconds(last_reply_timestamp,
wal_sender_timeout / 2);
/* Compute relative time until wakeup. */
TimestampDifference(now, wakeup_time,
&sec_to_timeout, &microsec_to_timeout);
sleeptime = sec_to_timeout * 1000 +
microsec_to_timeout / 1000;
}
return sleeptime;
}
/*
* Check whether there have been responses by the client within
* wal_sender_timeout and shutdown if not.
*/
static void
WalSndCheckTimeOut(TimestampTz now)
{
TimestampTz timeout;
/* don't bail out if we're doing something that doesn't require timeouts */
if (last_reply_timestamp <= 0)
return;
timeout = TimestampTzPlusMilliseconds(last_reply_timestamp,
wal_sender_timeout);
if (wal_sender_timeout > 0 && now >= timeout)
{
/*
* Since typically expiration of replication timeout means
* communication problem, we don't send the error message to the
* standby.
*/
ereport(COMMERROR,
(errmsg("terminating walsender process due to replication timeout")));
WalSndShutdown();
}
}
/* Main loop of walsender process that streams the WAL over Copy messages. */
static void
WalSndLoop(WalSndSendDataCallback send_data)
{
/*
* Allocate buffers that will be used for each outgoing and incoming
* message. We do this just once to reduce palloc overhead.
*/
initStringInfo(&output_message);
initStringInfo(&reply_message);
initStringInfo(&tmpbuf);
/*
* Initialize the last reply timestamp. That enables timeout processing
* from hereon.
*/
last_reply_timestamp = GetCurrentTimestamp();
waiting_for_ping_response = false;
/* Report to pgstat that this process is a WAL sender */
pgstat_report_activity(STATE_RUNNING, "walsender");
/*
* Loop until we reach the end of this timeline or the client requests to
* stop streaming.
*/
for (;;)
{
TimestampTz now;
/*
* Emergency bailout if postmaster has died. This is to avoid the
* necessity for manual cleanup of all postmaster children.
*/
if (!PostmasterIsAlive())
exit(1);
/* Clear any already-pending wakeups */
ResetLatch(MyLatch);
CHECK_FOR_INTERRUPTS();
/* Process any requests or signals received recently */
if (got_SIGHUP)
{
got_SIGHUP = false;
ProcessConfigFile(PGC_SIGHUP);
SyncRepInitConfig();
}
/* Check for input from the client */
ProcessRepliesIfAny();
/*
* If we have received CopyDone from the client, sent CopyDone
* ourselves, and the output buffer is empty, it's time to exit
* streaming.
*/
if (!pq_is_send_pending() && streamingDoneSending && streamingDoneReceiving)
break;
/*
* If we don't have any pending data in the output buffer, try to send
* some more. If there is some, we don't bother to call send_data
* again until we've flushed it ... but we'd better assume we are not
* caught up.
*/
if (!pq_is_send_pending())
send_data();
else
WalSndCaughtUp = false;
/* Try to flush pending output to the client */
if (pq_flush_if_writable() != 0)
WalSndShutdown();
/* If nothing remains to be sent right now ... */
if (WalSndCaughtUp && !pq_is_send_pending())
{
/*
* If we're in catchup state, move to streaming. This is an
* important state change for users to know about, since before
* this point data loss might occur if the primary dies and we
* need to failover to the standby. The state change is also
* important for synchronous replication, since commits that
* started to wait at that point might wait for some time.
*/
if (MyWalSnd->state == WALSNDSTATE_CATCHUP)
{
ereport(DEBUG1,
(errmsg("standby \"%s\" has now caught up with primary",
application_name)));
WalSndSetState(WALSNDSTATE_STREAMING);
}
/*
* When SIGUSR2 arrives, we send any outstanding logs up to the
* shutdown checkpoint record (i.e., the latest record), wait for
* them to be replicated to the standby, and exit. This may be a
* normal termination at shutdown, or a promotion, the walsender
* is not sure which.
*/
if (walsender_ready_to_stop)
WalSndDone(send_data);
}
now = GetCurrentTimestamp();
/* Check for replication timeout. */
WalSndCheckTimeOut(now);
/* Send keepalive if the time has come */
WalSndKeepaliveIfNecessary(now);
/*
* We don't block if not caught up, unless there is unsent data
* pending in which case we'd better block until the socket is
* write-ready. This test is only needed for the case where the
* send_data callback handled a subset of the available data but then
* pq_flush_if_writable flushed it all --- we should immediately try
* to send more.
*/
if ((WalSndCaughtUp && !streamingDoneSending) || pq_is_send_pending())
{
long sleeptime;
int wakeEvents;
wakeEvents = WL_LATCH_SET | WL_POSTMASTER_DEATH | WL_TIMEOUT |
WL_SOCKET_READABLE;
sleeptime = WalSndComputeSleeptime(now);
if (pq_is_send_pending())
wakeEvents |= WL_SOCKET_WRITEABLE;
/* Sleep until something happens or we time out */
WaitLatchOrSocket(MyLatch, wakeEvents,
MyProcPort->sock, sleeptime);
}
}
return;
}
/* Initialize a per-walsender data structure for this walsender process */
static void
InitWalSenderSlot(void)
{
int i;
/*
* WalSndCtl should be set up already (we inherit this by fork() or
* EXEC_BACKEND mechanism from the postmaster).
*/
Assert(WalSndCtl != NULL);
Assert(MyWalSnd == NULL);
/*
* Find a free walsender slot and reserve it. If this fails, we must be
* out of WalSnd structures.
*/
for (i = 0; i < max_wal_senders; i++)
{
WalSnd *walsnd = &WalSndCtl->walsnds[i];
SpinLockAcquire(&walsnd->mutex);
if (walsnd->pid != 0)
{
SpinLockRelease(&walsnd->mutex);
continue;
}
else
{
/*
* Found a free slot. Reserve it for us.
*/
walsnd->pid = MyProcPid;
walsnd->sentPtr = InvalidXLogRecPtr;
walsnd->write = InvalidXLogRecPtr;
walsnd->flush = InvalidXLogRecPtr;
walsnd->apply = InvalidXLogRecPtr;
walsnd->state = WALSNDSTATE_STARTUP;
walsnd->latch = &MyProc->procLatch;
SpinLockRelease(&walsnd->mutex);
/* don't need the lock anymore */
MyWalSnd = (WalSnd *) walsnd;
break;
}
}
if (MyWalSnd == NULL)
ereport(FATAL,
(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
errmsg("number of requested standby connections "
"exceeds max_wal_senders (currently %d)",
max_wal_senders)));
/* Arrange to clean up at walsender exit */
on_shmem_exit(WalSndKill, 0);
}
/* Destroy the per-walsender data structure for this walsender process */
static void
WalSndKill(int code, Datum arg)
{
WalSnd *walsnd = MyWalSnd;
Assert(walsnd != NULL);
MyWalSnd = NULL;
SpinLockAcquire(&walsnd->mutex);
/* clear latch while holding the spinlock, so it can safely be read */
walsnd->latch = NULL;
/* Mark WalSnd struct as no longer being in use. */
walsnd->pid = 0;
SpinLockRelease(&walsnd->mutex);
}
/*
* Read 'count' bytes from WAL into 'buf', starting at location 'startptr'
*
* XXX probably this should be improved to suck data directly from the
* WAL buffers when possible.
*
* Will open, and keep open, one WAL segment stored in the global file
* descriptor sendFile. This means if XLogRead is used once, there will
* always be one descriptor left open until the process ends, but never
* more than one.
*/
static void
XLogRead(char *buf, XLogRecPtr startptr, Size count)
{
char *p;
XLogRecPtr recptr;
Size nbytes;
XLogSegNo segno;
retry:
p = buf;
recptr = startptr;
nbytes = count;
while (nbytes > 0)
{
uint32 startoff;
int segbytes;
int readbytes;
startoff = recptr % XLogSegSize;
if (sendFile < 0 || !XLByteInSeg(recptr, sendSegNo))
{
char path[MAXPGPATH];
/* Switch to another logfile segment */
if (sendFile >= 0)
close(sendFile);
XLByteToSeg(recptr, sendSegNo);
/*-------
* When reading from a historic timeline, and there is a timeline
* switch within this segment, read from the WAL segment belonging
* to the new timeline.
*
* For example, imagine that this server is currently on timeline
* 5, and we're streaming timeline 4. The switch from timeline 4
* to 5 happened at 0/13002088. In pg_xlog, we have these files:
*
* ...
* 000000040000000000000012
* 000000040000000000000013
* 000000050000000000000013
* 000000050000000000000014
* ...
*
* In this situation, when requested to send the WAL from
* segment 0x13, on timeline 4, we read the WAL from file
* 000000050000000000000013. Archive recovery prefers files from
* newer timelines, so if the segment was restored from the
* archive on this server, the file belonging to the old timeline,
* 000000040000000000000013, might not exist. Their contents are
* equal up to the switchpoint, because at a timeline switch, the
* used portion of the old segment is copied to the new file.
*-------
*/
curFileTimeLine = sendTimeLine;
if (sendTimeLineIsHistoric)
{
XLogSegNo endSegNo;
XLByteToSeg(sendTimeLineValidUpto, endSegNo);
if (sendSegNo == endSegNo)
curFileTimeLine = sendTimeLineNextTLI;
}
XLogFilePath(path, curFileTimeLine, sendSegNo);
sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
if (sendFile < 0)
{
/*
* If the file is not found, assume it's because the standby
* asked for a too old WAL segment that has already been
* removed or recycled.
*/
if (errno == ENOENT)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("requested WAL segment %s has already been removed",
XLogFileNameP(curFileTimeLine, sendSegNo))));
else
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open file \"%s\": %m",
path)));
}
sendOff = 0;
}
/* Need to seek in the file? */
if (sendOff != startoff)
{
if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in log segment %s to offset %u: %m",
XLogFileNameP(curFileTimeLine, sendSegNo),
startoff)));
sendOff = startoff;
}
/* How many bytes are within this segment? */
if (nbytes > (XLogSegSize - startoff))
segbytes = XLogSegSize - startoff;
else
segbytes = nbytes;
readbytes = read(sendFile, p, segbytes);
if (readbytes <= 0)
{
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from log segment %s, offset %u, length %lu: %m",
XLogFileNameP(curFileTimeLine, sendSegNo),
sendOff, (unsigned long) segbytes)));
}
/* Update state for read */
recptr += readbytes;
sendOff += readbytes;
nbytes -= readbytes;
p += readbytes;
}
/*
* After reading into the buffer, check that what we read was valid. We do
* this after reading, because even though the segment was present when we
* opened it, it might get recycled or removed while we read it. The
* read() succeeds in that case, but the data we tried to read might
* already have been overwritten with new WAL records.
*/
XLByteToSeg(startptr, segno);
CheckXLogRemoved(segno, ThisTimeLineID);
/*
* During recovery, the currently-open WAL file might be replaced with the
* file of the same name retrieved from archive. So we always need to
* check what we read was valid after reading into the buffer. If it's
* invalid, we try to open and read the file again.
*/
if (am_cascading_walsender)
{
WalSnd *walsnd = MyWalSnd;
bool reload;
SpinLockAcquire(&walsnd->mutex);
reload = walsnd->needreload;
walsnd->needreload = false;
SpinLockRelease(&walsnd->mutex);
if (reload && sendFile >= 0)
{
close(sendFile);
sendFile = -1;
goto retry;
}
}
}
/*
* Send out the WAL in its normal physical/stored form.
*
* Read up to MAX_SEND_SIZE bytes of WAL that's been flushed to disk,
* but not yet sent to the client, and buffer it in the libpq output
* buffer.
*
* If there is no unsent WAL remaining, WalSndCaughtUp is set to true,
* otherwise WalSndCaughtUp is set to false.
*/
static void
XLogSendPhysical(void)
{
XLogRecPtr SendRqstPtr;
XLogRecPtr startptr;
XLogRecPtr endptr;
Size nbytes;
if (streamingDoneSending)
{
WalSndCaughtUp = true;
return;
}
/* Figure out how far we can safely send the WAL. */
if (sendTimeLineIsHistoric)
{
/*
* Streaming an old timeline that's in this server's history, but is
* not the one we're currently inserting or replaying. It can be
* streamed up to the point where we switched off that timeline.
*/
SendRqstPtr = sendTimeLineValidUpto;
}
else if (am_cascading_walsender)
{
/*
* Streaming the latest timeline on a standby.
*
* Attempt to send all WAL that has already been replayed, so that we
* know it's valid. If we're receiving WAL through streaming
* replication, it's also OK to send any WAL that has been received
* but not replayed.
*
* The timeline we're recovering from can change, or we can be
* promoted. In either case, the current timeline becomes historic. We
* need to detect that so that we don't try to stream past the point
* where we switched to another timeline. We check for promotion or
* timeline switch after calculating FlushPtr, to avoid a race
* condition: if the timeline becomes historic just after we checked
* that it was still current, it's still be OK to stream it up to the
* FlushPtr that was calculated before it became historic.
*/
bool becameHistoric = false;
SendRqstPtr = GetStandbyFlushRecPtr();
if (!RecoveryInProgress())
{
/*
* We have been promoted. RecoveryInProgress() updated
* ThisTimeLineID to the new current timeline.
*/
am_cascading_walsender = false;
becameHistoric = true;
}
else
{
/*
* Still a cascading standby. But is the timeline we're sending
* still the one recovery is recovering from? ThisTimeLineID was
* updated by the GetStandbyFlushRecPtr() call above.
*/
if (sendTimeLine != ThisTimeLineID)
becameHistoric = true;
}
if (becameHistoric)
{
/*
* The timeline we were sending has become historic. Read the
* timeline history file of the new timeline to see where exactly
* we forked off from the timeline we were sending.
*/
List *history;
history = readTimeLineHistory(ThisTimeLineID);
sendTimeLineValidUpto = tliSwitchPoint(sendTimeLine, history, &sendTimeLineNextTLI);
Assert(sendTimeLine < sendTimeLineNextTLI);
list_free_deep(history);
sendTimeLineIsHistoric = true;
SendRqstPtr = sendTimeLineValidUpto;
}
}
else
{
/*
* Streaming the current timeline on a master.
*
* Attempt to send all data that's already been written out and
* fsync'd to disk. We cannot go further than what's been written out
* given the current implementation of XLogRead(). And in any case
* it's unsafe to send WAL that is not securely down to disk on the
* master: if the master subsequently crashes and restarts, slaves
* must not have applied any WAL that gets lost on the master.
*/
SendRqstPtr = GetFlushRecPtr();
}
/*
* If this is a historic timeline and we've reached the point where we
* forked to the next timeline, stop streaming.
*
* Note: We might already have sent WAL > sendTimeLineValidUpto. The
* startup process will normally replay all WAL that has been received
* from the master, before promoting, but if the WAL streaming is
* terminated at a WAL page boundary, the valid portion of the timeline
* might end in the middle of a WAL record. We might've already sent the
* first half of that partial WAL record to the cascading standby, so that
* sentPtr > sendTimeLineValidUpto. That's OK; the cascading standby can't
* replay the partial WAL record either, so it can still follow our
* timeline switch.
*/
if (sendTimeLineIsHistoric && sendTimeLineValidUpto <= sentPtr)
{
/* close the current file. */
if (sendFile >= 0)
close(sendFile);
sendFile = -1;
/* Send CopyDone */
pq_putmessage_noblock('c', NULL, 0);
streamingDoneSending = true;
WalSndCaughtUp = true;
elog(DEBUG1, "walsender reached end of timeline at %X/%X (sent up to %X/%X)",
(uint32) (sendTimeLineValidUpto >> 32), (uint32) sendTimeLineValidUpto,
(uint32) (sentPtr >> 32), (uint32) sentPtr);
return;
}
/* Do we have any work to do? */
Assert(sentPtr <= SendRqstPtr);
if (SendRqstPtr <= sentPtr)
{
WalSndCaughtUp = true;
return;
}
/*
* Figure out how much to send in one message. If there's no more than
* MAX_SEND_SIZE bytes to send, send everything. Otherwise send
* MAX_SEND_SIZE bytes, but round back to logfile or page boundary.
*
* The rounding is not only for performance reasons. Walreceiver relies on
* the fact that we never split a WAL record across two messages. Since a
* long WAL record is split at page boundary into continuation records,
* page boundary is always a safe cut-off point. We also assume that
* SendRqstPtr never points to the middle of a WAL record.
*/
startptr = sentPtr;
endptr = startptr;
endptr += MAX_SEND_SIZE;
/* if we went beyond SendRqstPtr, back off */
if (SendRqstPtr <= endptr)
{
endptr = SendRqstPtr;
if (sendTimeLineIsHistoric)
WalSndCaughtUp = false;
else
WalSndCaughtUp = true;
}
else
{
/* round down to page boundary. */
endptr -= (endptr % XLOG_BLCKSZ);
WalSndCaughtUp = false;
}
nbytes = endptr - startptr;
Assert(nbytes <= MAX_SEND_SIZE);
/*
* OK to read and send the slice.
*/
resetStringInfo(&output_message);
pq_sendbyte(&output_message, 'w');
pq_sendint64(&output_message, startptr); /* dataStart */
pq_sendint64(&output_message, SendRqstPtr); /* walEnd */
pq_sendint64(&output_message, 0); /* sendtime, filled in last */
/*
* Read the log directly into the output buffer to avoid extra memcpy
* calls.
*/
enlargeStringInfo(&output_message, nbytes);
XLogRead(&output_message.data[output_message.len], startptr, nbytes);
output_message.len += nbytes;
output_message.data[output_message.len] = '\0';
/*
* Fill the send timestamp last, so that it is taken as late as possible.
*/
resetStringInfo(&tmpbuf);
pq_sendint64(&tmpbuf, GetCurrentIntegerTimestamp());
memcpy(&output_message.data[1 + sizeof(int64) + sizeof(int64)],
tmpbuf.data, sizeof(int64));
pq_putmessage_noblock('d', output_message.data, output_message.len);
sentPtr = endptr;
/* Update shared memory status */
{
WalSnd *walsnd = MyWalSnd;
SpinLockAcquire(&walsnd->mutex);
walsnd->sentPtr = sentPtr;
SpinLockRelease(&walsnd->mutex);
}
/* Report progress of XLOG streaming in PS display */
if (update_process_title)
{
char activitymsg[50];
snprintf(activitymsg, sizeof(activitymsg), "streaming %X/%X",
(uint32) (sentPtr >> 32), (uint32) sentPtr);
set_ps_display(activitymsg, false);
}
return;
}
/*
* Stream out logically decoded data.
*/
static void
XLogSendLogical(void)
{
XLogRecord *record;
char *errm;
/*
* Don't know whether we've caught up yet. We'll set it to true in
* WalSndWaitForWal, if we're actually waiting. We also set to true if
* XLogReadRecord() had to stop reading but WalSndWaitForWal didn't wait -
* i.e. when we're shutting down.
*/
WalSndCaughtUp = false;
record = XLogReadRecord(logical_decoding_ctx->reader, logical_startptr, &errm);
logical_startptr = InvalidXLogRecPtr;
/* xlog record was invalid */
if (errm != NULL)
elog(ERROR, "%s", errm);
if (record != NULL)
{
LogicalDecodingProcessRecord(logical_decoding_ctx, logical_decoding_ctx->reader);
sentPtr = logical_decoding_ctx->reader->EndRecPtr;
}
else
{
/*
* If the record we just wanted read is at or beyond the flushed
* point, then we're caught up.
*/
if (logical_decoding_ctx->reader->EndRecPtr >= GetFlushRecPtr())
WalSndCaughtUp = true;
}
/* Update shared memory status */
{
WalSnd *walsnd = MyWalSnd;
SpinLockAcquire(&walsnd->mutex);
walsnd->sentPtr = sentPtr;
SpinLockRelease(&walsnd->mutex);
}
}
/*
* Shutdown if the sender is caught up.
*
* NB: This should only be called when the shutdown signal has been received
* from postmaster.
*
* Note that if we determine that there's still more data to send, this
* function will return control to the caller.
*/
static void
WalSndDone(WalSndSendDataCallback send_data)
{
XLogRecPtr replicatedPtr;
/* ... let's just be real sure we're caught up ... */
send_data();
/*
* To figure out whether all WAL has successfully been replicated, check
* flush location if valid, write otherwise. Tools like pg_receivexlog
* will usually (unless in synchronous mode) return an invalid flush
* location.
*/
replicatedPtr = XLogRecPtrIsInvalid(MyWalSnd->flush) ?
MyWalSnd->write : MyWalSnd->flush;
if (WalSndCaughtUp && sentPtr == replicatedPtr &&
!pq_is_send_pending())
{
/* Inform the standby that XLOG streaming is done */
EndCommand("COPY 0", DestRemote);
pq_flush();
proc_exit(0);
}
if (!waiting_for_ping_response)
{
WalSndKeepalive(true);
waiting_for_ping_response = true;
}
}
/*
* Returns the latest point in WAL that has been safely flushed to disk, and
* can be sent to the standby. This should only be called when in recovery,
* ie. we're streaming to a cascaded standby.
*
* As a side-effect, ThisTimeLineID is updated to the TLI of the last
* replayed WAL record.
*/
static XLogRecPtr
GetStandbyFlushRecPtr(void)
{
XLogRecPtr replayPtr;
TimeLineID replayTLI;
XLogRecPtr receivePtr;
TimeLineID receiveTLI;
XLogRecPtr result;
/*
* We can safely send what's already been replayed. Also, if walreceiver
* is streaming WAL from the same timeline, we can send anything that it
* has streamed, but hasn't been replayed yet.
*/
receivePtr = GetWalRcvWriteRecPtr(NULL, &receiveTLI);
replayPtr = GetXLogReplayRecPtr(&replayTLI);
ThisTimeLineID = replayTLI;
result = replayPtr;
if (receiveTLI == ThisTimeLineID && receivePtr > replayPtr)
result = receivePtr;
return result;
}
/*
* Request walsenders to reload the currently-open WAL file
*/
void
WalSndRqstFileReload(void)
{
int i;
for (i = 0; i < max_wal_senders; i++)
{
WalSnd *walsnd = &WalSndCtl->walsnds[i];
if (walsnd->pid == 0)
continue;
SpinLockAcquire(&walsnd->mutex);
walsnd->needreload = true;
SpinLockRelease(&walsnd->mutex);
}
}
/* SIGHUP: set flag to re-read config file at next convenient time */
static void
WalSndSigHupHandler(SIGNAL_ARGS)
{
int save_errno = errno;
got_SIGHUP = true;
SetLatch(MyLatch);
errno = save_errno;
}
/* SIGUSR1: set flag to send WAL records */
static void
WalSndXLogSendHandler(SIGNAL_ARGS)
{
int save_errno = errno;
latch_sigusr1_handler();
errno = save_errno;
}
/* SIGUSR2: set flag to do a last cycle and shut down afterwards */
static void
WalSndLastCycleHandler(SIGNAL_ARGS)
{
int save_errno = errno;
/*
* If replication has not yet started, die like with SIGTERM. If
* replication is active, only set a flag and wake up the main loop. It
* will send any outstanding WAL, wait for it to be replicated to the
* standby, and then exit gracefully.
*/
if (!replication_active)
kill(MyProcPid, SIGTERM);
walsender_ready_to_stop = true;
SetLatch(MyLatch);
errno = save_errno;
}
/* Set up signal handlers */
void
WalSndSignals(void)
{
/* Set up signal handlers */
pqsignal(SIGHUP, WalSndSigHupHandler); /* set flag to read config
* file */
pqsignal(SIGINT, SIG_IGN); /* not used */
pqsignal(SIGTERM, die); /* request shutdown */
pqsignal(SIGQUIT, quickdie); /* hard crash time */
InitializeTimeouts(); /* establishes SIGALRM handler */
pqsignal(SIGPIPE, SIG_IGN);
pqsignal(SIGUSR1, WalSndXLogSendHandler); /* request WAL sending */
pqsignal(SIGUSR2, WalSndLastCycleHandler); /* request a last cycle and
* shutdown */
/* Reset some signals that are accepted by postmaster but not here */
pqsignal(SIGCHLD, SIG_DFL);
pqsignal(SIGTTIN, SIG_DFL);
pqsignal(SIGTTOU, SIG_DFL);
pqsignal(SIGCONT, SIG_DFL);
pqsignal(SIGWINCH, SIG_DFL);
}
/* Report shared-memory space needed by WalSndShmemInit */
Size
WalSndShmemSize(void)
{
Size size = 0;
size = offsetof(WalSndCtlData, walsnds);
size = add_size(size, mul_size(max_wal_senders, sizeof(WalSnd)));
return size;
}
/* Allocate and initialize walsender-related shared memory */
void
WalSndShmemInit(void)
{
bool found;
int i;
WalSndCtl = (WalSndCtlData *)
ShmemInitStruct("Wal Sender Ctl", WalSndShmemSize(), &found);
if (!found)
{
/* First time through, so initialize */
MemSet(WalSndCtl, 0, WalSndShmemSize());
for (i = 0; i < NUM_SYNC_REP_WAIT_MODE; i++)
SHMQueueInit(&(WalSndCtl->SyncRepQueue[i]));
for (i = 0; i < max_wal_senders; i++)
{
WalSnd *walsnd = &WalSndCtl->walsnds[i];
SpinLockInit(&walsnd->mutex);
}
}
}
/*
* Wake up all walsenders
*
* This will be called inside critical sections, so throwing an error is not
* adviseable.
*/
void
WalSndWakeup(void)
{
int i;
for (i = 0; i < max_wal_senders; i++)
{
Latch *latch;
WalSnd *walsnd = &WalSndCtl->walsnds[i];
/*
* Get latch pointer with spinlock held, for the unlikely case that
* pointer reads aren't atomic (as they're 8 bytes).
*/
SpinLockAcquire(&walsnd->mutex);
latch = walsnd->latch;
SpinLockRelease(&walsnd->mutex);
if (latch != NULL)
SetLatch(latch);
}
}
/* Set state for current walsender (only called in walsender) */
void
WalSndSetState(WalSndState state)
{
WalSnd *walsnd = MyWalSnd;
Assert(am_walsender);
if (walsnd->state == state)
return;
SpinLockAcquire(&walsnd->mutex);
walsnd->state = state;
SpinLockRelease(&walsnd->mutex);
}
/*
* Return a string constant representing the state. This is used
* in system views, and should *not* be translated.
*/
static const char *
WalSndGetStateString(WalSndState state)
{
switch (state)
{
case WALSNDSTATE_STARTUP:
return "startup";
case WALSNDSTATE_BACKUP:
return "backup";
case WALSNDSTATE_CATCHUP:
return "catchup";
case WALSNDSTATE_STREAMING:
return "streaming";
}
return "UNKNOWN";
}
/*
* Returns activity of walsenders, including pids and xlog locations sent to
* standby servers.
*/
Datum
pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
{
#define PG_STAT_GET_WAL_SENDERS_COLS 8
ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
TupleDesc tupdesc;
Tuplestorestate *tupstore;
MemoryContext per_query_ctx;
MemoryContext oldcontext;
List *sync_standbys;
int i;
/* check to see if caller supports us returning a tuplestore */
if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("set-valued function called in context that cannot accept a set")));
if (!(rsinfo->allowedModes & SFRM_Materialize))
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("materialize mode required, but it is not " \
"allowed in this context")));
/* Build a tuple descriptor for our result type */
if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
elog(ERROR, "return type must be a row type");
per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
oldcontext = MemoryContextSwitchTo(per_query_ctx);
tupstore = tuplestore_begin_heap(true, false, work_mem);
rsinfo->returnMode = SFRM_Materialize;
rsinfo->setResult = tupstore;
rsinfo->setDesc = tupdesc;
MemoryContextSwitchTo(oldcontext);
/*
* Get the currently active synchronous standbys.
*/
LWLockAcquire(SyncRepLock, LW_SHARED);
sync_standbys = SyncRepGetSyncStandbys(NULL);
LWLockRelease(SyncRepLock);
for (i = 0; i < max_wal_senders; i++)
{
WalSnd *walsnd = &WalSndCtl->walsnds[i];
XLogRecPtr sentPtr;
XLogRecPtr write;
XLogRecPtr flush;
XLogRecPtr apply;
int priority;
WalSndState state;
Datum values[PG_STAT_GET_WAL_SENDERS_COLS];
bool nulls[PG_STAT_GET_WAL_SENDERS_COLS];
if (walsnd->pid == 0)
continue;
SpinLockAcquire(&walsnd->mutex);
sentPtr = walsnd->sentPtr;
state = walsnd->state;
write = walsnd->write;
flush = walsnd->flush;
apply = walsnd->apply;
priority = walsnd->sync_standby_priority;
SpinLockRelease(&walsnd->mutex);
memset(nulls, 0, sizeof(nulls));
values[0] = Int32GetDatum(walsnd->pid);
if (!superuser())
{
/*
* Only superusers can see details. Other users only get the pid
* value to know it's a walsender, but no details.
*/
MemSet(&nulls[1], true, PG_STAT_GET_WAL_SENDERS_COLS - 1);
}
else
{
values[1] = CStringGetTextDatum(WalSndGetStateString(state));
if (XLogRecPtrIsInvalid(sentPtr))
nulls[2] = true;
values[2] = LSNGetDatum(sentPtr);
if (XLogRecPtrIsInvalid(write))
nulls[3] = true;
values[3] = LSNGetDatum(write);
if (XLogRecPtrIsInvalid(flush))
nulls[4] = true;
values[4] = LSNGetDatum(flush);
if (XLogRecPtrIsInvalid(apply))
nulls[5] = true;
values[5] = LSNGetDatum(apply);
/*
* Treat a standby such as a pg_basebackup background process
* which always returns an invalid flush location, as an
* asynchronous standby.
*/
priority = XLogRecPtrIsInvalid(walsnd->flush) ? 0 : priority;
values[6] = Int32GetDatum(priority);
/*
* More easily understood version of standby state. This is purely
* informational, not different from priority.
*/
if (priority == 0)
values[7] = CStringGetTextDatum("async");
else if (list_member_int(sync_standbys, i))
values[7] = CStringGetTextDatum("sync");
else
values[7] = CStringGetTextDatum("potential");
}
tuplestore_putvalues(tupstore, tupdesc, values, nulls);
}
/* clean up and return the tuplestore */
tuplestore_donestoring(tupstore);
return (Datum) 0;
}
/*
* This function is used to send keepalive message to standby.
* If requestReply is set, sets a flag in the message requesting the standby
* to send a message back to us, for heartbeat purposes.
*/
static void
WalSndKeepalive(bool requestReply)
{
elog(DEBUG2, "sending replication keepalive");
/* construct the message... */
resetStringInfo(&output_message);
pq_sendbyte(&output_message, 'k');
pq_sendint64(&output_message, sentPtr);
pq_sendint64(&output_message, GetCurrentIntegerTimestamp());
pq_sendbyte(&output_message, requestReply ? 1 : 0);
/* ... and send it wrapped in CopyData */
pq_putmessage_noblock('d', output_message.data, output_message.len);
}
/*
* Send keepalive message if too much time has elapsed.
*/
static void
WalSndKeepaliveIfNecessary(TimestampTz now)
{
TimestampTz ping_time;
/*
* Don't send keepalive messages if timeouts are globally disabled or
* we're doing something not partaking in timeouts.
*/
if (wal_sender_timeout <= 0 || last_reply_timestamp <= 0)
return;
if (waiting_for_ping_response)
return;
/*
* If half of wal_sender_timeout has lapsed without receiving any reply
* from the standby, send a keep-alive message to the standby requesting
* an immediate reply.
*/
ping_time = TimestampTzPlusMilliseconds(last_reply_timestamp,
wal_sender_timeout / 2);
if (now >= ping_time)
{
WalSndKeepalive(true);
waiting_for_ping_response = true;
/* Try to flush pending output to the client */
if (pq_flush_if_writable() != 0)
WalSndShutdown();
}
}
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