2010-01-15 10:19:10 +01:00
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/*-------------------------------------------------------------------------
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*
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* walsender.h
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* Exports from replication/walsender.c.
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*
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* Portions Copyright (c) 2010-2010, PostgreSQL Global Development Group
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*
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Introduce latches. A latch is a boolean variable, with the capability to
wait until it is set. Latches can be used to reliably wait until a signal
arrives, which is hard otherwise because signals don't interrupt select()
on some platforms, and even when they do, there's race conditions.
On Unix, latches use the so called self-pipe trick under the covers to
implement the sleep until the latch is set, without race conditions. On
Windows, Windows events are used.
Use the new latch abstraction to sleep in walsender, so that as soon as
a transaction finishes, walsender is woken up to immediately send the WAL
to the standby. This reduces the latency between master and standby, which
is good.
Preliminary work by Fujii Masao. The latch implementation is by me, with
helpful comments from many people.
2010-09-11 17:48:04 +02:00
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* $PostgreSQL: pgsql/src/include/replication/walsender.h,v 1.5 2010/09/11 15:48:04 heikki Exp $
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2010-01-15 10:19:10 +01:00
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef _WALSENDER_H
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#define _WALSENDER_H
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#include "access/xlog.h"
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Introduce latches. A latch is a boolean variable, with the capability to
wait until it is set. Latches can be used to reliably wait until a signal
arrives, which is hard otherwise because signals don't interrupt select()
on some platforms, and even when they do, there's race conditions.
On Unix, latches use the so called self-pipe trick under the covers to
implement the sleep until the latch is set, without race conditions. On
Windows, Windows events are used.
Use the new latch abstraction to sleep in walsender, so that as soon as
a transaction finishes, walsender is woken up to immediately send the WAL
to the standby. This reduces the latency between master and standby, which
is good.
Preliminary work by Fujii Masao. The latch implementation is by me, with
helpful comments from many people.
2010-09-11 17:48:04 +02:00
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#include "storage/latch.h"
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2010-01-15 10:19:10 +01:00
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#include "storage/spin.h"
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/*
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* Each walsender has a WalSnd struct in shared memory.
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*/
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typedef struct WalSnd
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{
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2010-02-26 03:01:40 +01:00
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pid_t pid; /* this walsender's process id, or 0 */
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XLogRecPtr sentPtr; /* WAL has been sent up to this point */
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2010-01-15 10:19:10 +01:00
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2010-02-26 03:01:40 +01:00
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slock_t mutex; /* locks shared variables shown above */
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Introduce latches. A latch is a boolean variable, with the capability to
wait until it is set. Latches can be used to reliably wait until a signal
arrives, which is hard otherwise because signals don't interrupt select()
on some platforms, and even when they do, there's race conditions.
On Unix, latches use the so called self-pipe trick under the covers to
implement the sleep until the latch is set, without race conditions. On
Windows, Windows events are used.
Use the new latch abstraction to sleep in walsender, so that as soon as
a transaction finishes, walsender is woken up to immediately send the WAL
to the standby. This reduces the latency between master and standby, which
is good.
Preliminary work by Fujii Masao. The latch implementation is by me, with
helpful comments from many people.
2010-09-11 17:48:04 +02:00
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/*
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* Latch used by backends to wake up this walsender when it has work
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* to do.
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*/
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Latch latch;
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2010-01-15 10:19:10 +01:00
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} WalSnd;
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/* There is one WalSndCtl struct for the whole database cluster */
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typedef struct
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{
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2010-02-26 03:01:40 +01:00
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WalSnd walsnds[1]; /* VARIABLE LENGTH ARRAY */
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2010-01-15 10:19:10 +01:00
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} WalSndCtlData;
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extern WalSndCtlData *WalSndCtl;
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/* global state */
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2010-02-26 03:01:40 +01:00
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extern bool am_walsender;
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2010-01-15 10:19:10 +01:00
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/* user-settable parameters */
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extern int WalSndDelay;
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Introduce wal_level GUC to explicitly control if information needed for
archival or hot standby should be WAL-logged, instead of deducing that from
other options like archive_mode. This replaces recovery_connections GUC in
the primary, where it now has no effect, but it's still used in the standby
to enable/disable hot standby.
Remove the WAL-logging of "unlogged operations", like creating an index
without WAL-logging and fsyncing it at the end. Instead, we keep a copy of
the wal_mode setting and the settings that affect how much shared memory a
hot standby server needs to track master transactions (max_connections,
max_prepared_xacts, max_locks_per_xact) in pg_control. Whenever the settings
change, at server restart, write a WAL record noting the new settings and
update pg_control. This allows us to notice the change in those settings in
the standby at the right moment, they used to be included in checkpoint
records, but that meant that a changed value was not reflected in the
standby until the first checkpoint after the change.
Bump PG_CONTROL_VERSION and XLOG_PAGE_MAGIC. Whack XLOG_PAGE_MAGIC back to
the sequence it used to follow, before hot standby and subsequent patches
changed it to 0x9003.
2010-04-28 18:10:43 +02:00
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extern int max_wal_senders;
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2010-01-15 10:19:10 +01:00
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2010-02-26 03:01:40 +01:00
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extern int WalSenderMain(void);
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2010-01-15 10:19:10 +01:00
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extern void WalSndSignals(void);
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extern Size WalSndShmemSize(void);
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extern void WalSndShmemInit(void);
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Introduce latches. A latch is a boolean variable, with the capability to
wait until it is set. Latches can be used to reliably wait until a signal
arrives, which is hard otherwise because signals don't interrupt select()
on some platforms, and even when they do, there's race conditions.
On Unix, latches use the so called self-pipe trick under the covers to
implement the sleep until the latch is set, without race conditions. On
Windows, Windows events are used.
Use the new latch abstraction to sleep in walsender, so that as soon as
a transaction finishes, walsender is woken up to immediately send the WAL
to the standby. This reduces the latency between master and standby, which
is good.
Preliminary work by Fujii Masao. The latch implementation is by me, with
helpful comments from many people.
2010-09-11 17:48:04 +02:00
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extern void WalSndWakeup(void);
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2010-01-15 10:19:10 +01:00
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2010-02-26 03:01:40 +01:00
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#endif /* _WALSENDER_H */
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