mirror of
https://git.postgresql.org/git/postgresql.git
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717 lines
22 KiB
C
717 lines
22 KiB
C
/*-------------------------------------------------------------------------
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*
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* connection.c
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* Connection management functions for postgres_fdw
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*
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* Portions Copyright (c) 2012-2016, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/postgres_fdw/connection.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "postgres_fdw.h"
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#include "access/xact.h"
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#include "mb/pg_wchar.h"
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#include "miscadmin.h"
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#include "utils/hsearch.h"
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#include "utils/memutils.h"
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/*
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* Connection cache hash table entry
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*
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* The lookup key in this hash table is the user mapping OID. We use just one
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* connection per user mapping ID, which ensures that all the scans use the
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* same snapshot during a query. Using the user mapping OID rather than
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* the foreign server OID + user OID avoids creating multiple connections when
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* the public user mapping applies to all user OIDs.
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*
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* The "conn" pointer can be NULL if we don't currently have a live connection.
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* When we do have a connection, xact_depth tracks the current depth of
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* transactions and subtransactions open on the remote side. We need to issue
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* commands at the same nesting depth on the remote as we're executing at
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* ourselves, so that rolling back a subtransaction will kill the right
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* queries and not the wrong ones.
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*/
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typedef Oid ConnCacheKey;
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typedef struct ConnCacheEntry
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{
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ConnCacheKey key; /* hash key (must be first) */
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PGconn *conn; /* connection to foreign server, or NULL */
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int xact_depth; /* 0 = no xact open, 1 = main xact open, 2 =
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* one level of subxact open, etc */
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bool have_prep_stmt; /* have we prepared any stmts in this xact? */
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bool have_error; /* have any subxacts aborted in this xact? */
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} ConnCacheEntry;
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/*
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* Connection cache (initialized on first use)
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*/
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static HTAB *ConnectionHash = NULL;
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/* for assigning cursor numbers and prepared statement numbers */
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static unsigned int cursor_number = 0;
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static unsigned int prep_stmt_number = 0;
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/* tracks whether any work is needed in callback functions */
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static bool xact_got_connection = false;
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/* prototypes of private functions */
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static PGconn *connect_pg_server(ForeignServer *server, UserMapping *user);
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static void check_conn_params(const char **keywords, const char **values);
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static void configure_remote_session(PGconn *conn);
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static void do_sql_command(PGconn *conn, const char *sql);
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static void begin_remote_xact(ConnCacheEntry *entry);
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static void pgfdw_xact_callback(XactEvent event, void *arg);
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static void pgfdw_subxact_callback(SubXactEvent event,
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SubTransactionId mySubid,
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SubTransactionId parentSubid,
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void *arg);
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/*
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* Get a PGconn which can be used to execute queries on the remote PostgreSQL
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* server with the user's authorization. A new connection is established
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* if we don't already have a suitable one, and a transaction is opened at
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* the right subtransaction nesting depth if we didn't do that already.
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*
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* will_prep_stmt must be true if caller intends to create any prepared
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* statements. Since those don't go away automatically at transaction end
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* (not even on error), we need this flag to cue manual cleanup.
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*
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* XXX Note that caching connections theoretically requires a mechanism to
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* detect change of FDW objects to invalidate already established connections.
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* We could manage that by watching for invalidation events on the relevant
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* syscaches. For the moment, though, it's not clear that this would really
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* be useful and not mere pedantry. We could not flush any active connections
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* mid-transaction anyway.
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*/
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PGconn *
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GetConnection(UserMapping *user, bool will_prep_stmt)
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{
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bool found;
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ConnCacheEntry *entry;
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ConnCacheKey key;
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/* First time through, initialize connection cache hashtable */
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if (ConnectionHash == NULL)
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{
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HASHCTL ctl;
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MemSet(&ctl, 0, sizeof(ctl));
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ctl.keysize = sizeof(ConnCacheKey);
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ctl.entrysize = sizeof(ConnCacheEntry);
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/* allocate ConnectionHash in the cache context */
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ctl.hcxt = CacheMemoryContext;
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ConnectionHash = hash_create("postgres_fdw connections", 8,
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&ctl,
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HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
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/*
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* Register some callback functions that manage connection cleanup.
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* This should be done just once in each backend.
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*/
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RegisterXactCallback(pgfdw_xact_callback, NULL);
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RegisterSubXactCallback(pgfdw_subxact_callback, NULL);
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}
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/* Set flag that we did GetConnection during the current transaction */
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xact_got_connection = true;
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/* Create hash key for the entry. Assume no pad bytes in key struct */
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key = user->umid;
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/*
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* Find or create cached entry for requested connection.
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*/
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entry = hash_search(ConnectionHash, &key, HASH_ENTER, &found);
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if (!found)
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{
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/* initialize new hashtable entry (key is already filled in) */
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entry->conn = NULL;
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entry->xact_depth = 0;
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entry->have_prep_stmt = false;
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entry->have_error = false;
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}
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/*
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* We don't check the health of cached connection here, because it would
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* require some overhead. Broken connection will be detected when the
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* connection is actually used.
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*/
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/*
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* If cache entry doesn't have a connection, we have to establish a new
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* connection. (If connect_pg_server throws an error, the cache entry
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* will be left in a valid empty state.)
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*/
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if (entry->conn == NULL)
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{
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ForeignServer *server = GetForeignServer(user->serverid);
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entry->xact_depth = 0; /* just to be sure */
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entry->have_prep_stmt = false;
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entry->have_error = false;
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entry->conn = connect_pg_server(server, user);
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elog(DEBUG3, "new postgres_fdw connection %p for server \"%s\" (user mapping oid %d, userid %d)",
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entry->conn, server->servername, user->umid, user->userid);
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}
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/*
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* Start a new transaction or subtransaction if needed.
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*/
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begin_remote_xact(entry);
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/* Remember if caller will prepare statements */
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entry->have_prep_stmt |= will_prep_stmt;
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return entry->conn;
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}
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/*
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* Connect to remote server using specified server and user mapping properties.
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*/
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static PGconn *
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connect_pg_server(ForeignServer *server, UserMapping *user)
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{
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PGconn *volatile conn = NULL;
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/*
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* Use PG_TRY block to ensure closing connection on error.
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*/
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PG_TRY();
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{
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const char **keywords;
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const char **values;
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int n;
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/*
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* Construct connection params from generic options of ForeignServer
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* and UserMapping. (Some of them might not be libpq options, in
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* which case we'll just waste a few array slots.) Add 3 extra slots
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* for fallback_application_name, client_encoding, end marker.
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*/
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n = list_length(server->options) + list_length(user->options) + 3;
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keywords = (const char **) palloc(n * sizeof(char *));
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values = (const char **) palloc(n * sizeof(char *));
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n = 0;
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n += ExtractConnectionOptions(server->options,
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keywords + n, values + n);
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n += ExtractConnectionOptions(user->options,
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keywords + n, values + n);
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/* Use "postgres_fdw" as fallback_application_name. */
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keywords[n] = "fallback_application_name";
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values[n] = "postgres_fdw";
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n++;
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/* Set client_encoding so that libpq can convert encoding properly. */
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keywords[n] = "client_encoding";
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values[n] = GetDatabaseEncodingName();
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n++;
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keywords[n] = values[n] = NULL;
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/* verify connection parameters and make connection */
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check_conn_params(keywords, values);
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conn = PQconnectdbParams(keywords, values, false);
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if (!conn || PQstatus(conn) != CONNECTION_OK)
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{
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char *connmessage;
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int msglen;
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/* libpq typically appends a newline, strip that */
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connmessage = pstrdup(PQerrorMessage(conn));
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msglen = strlen(connmessage);
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if (msglen > 0 && connmessage[msglen - 1] == '\n')
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connmessage[msglen - 1] = '\0';
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ereport(ERROR,
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(errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
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errmsg("could not connect to server \"%s\"",
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server->servername),
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errdetail_internal("%s", connmessage)));
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}
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/*
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* Check that non-superuser has used password to establish connection;
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* otherwise, he's piggybacking on the postgres server's user
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* identity. See also dblink_security_check() in contrib/dblink.
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*/
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if (!superuser() && !PQconnectionUsedPassword(conn))
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ereport(ERROR,
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(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
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errmsg("password is required"),
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errdetail("Non-superuser cannot connect if the server does not request a password."),
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errhint("Target server's authentication method must be changed.")));
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/* Prepare new session for use */
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configure_remote_session(conn);
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pfree(keywords);
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pfree(values);
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}
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PG_CATCH();
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{
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/* Release PGconn data structure if we managed to create one */
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if (conn)
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PQfinish(conn);
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PG_RE_THROW();
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}
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PG_END_TRY();
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return conn;
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}
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/*
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* For non-superusers, insist that the connstr specify a password. This
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* prevents a password from being picked up from .pgpass, a service file,
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* the environment, etc. We don't want the postgres user's passwords
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* to be accessible to non-superusers. (See also dblink_connstr_check in
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* contrib/dblink.)
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*/
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static void
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check_conn_params(const char **keywords, const char **values)
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{
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int i;
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/* no check required if superuser */
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if (superuser())
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return;
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/* ok if params contain a non-empty password */
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for (i = 0; keywords[i] != NULL; i++)
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{
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if (strcmp(keywords[i], "password") == 0 && values[i][0] != '\0')
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return;
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}
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ereport(ERROR,
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(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
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errmsg("password is required"),
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errdetail("Non-superusers must provide a password in the user mapping.")));
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}
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/*
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* Issue SET commands to make sure remote session is configured properly.
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*
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* We do this just once at connection, assuming nothing will change the
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* values later. Since we'll never send volatile function calls to the
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* remote, there shouldn't be any way to break this assumption from our end.
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* It's possible to think of ways to break it at the remote end, eg making
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* a foreign table point to a view that includes a set_config call ---
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* but once you admit the possibility of a malicious view definition,
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* there are any number of ways to break things.
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*/
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static void
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configure_remote_session(PGconn *conn)
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{
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int remoteversion = PQserverVersion(conn);
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/* Force the search path to contain only pg_catalog (see deparse.c) */
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do_sql_command(conn, "SET search_path = pg_catalog");
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/*
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* Set remote timezone; this is basically just cosmetic, since all
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* transmitted and returned timestamptzs should specify a zone explicitly
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* anyway. However it makes the regression test outputs more predictable.
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*
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* We don't risk setting remote zone equal to ours, since the remote
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* server might use a different timezone database. Instead, use UTC
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* (quoted, because very old servers are picky about case).
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*/
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do_sql_command(conn, "SET timezone = 'UTC'");
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/*
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* Set values needed to ensure unambiguous data output from remote. (This
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* logic should match what pg_dump does. See also set_transmission_modes
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* in postgres_fdw.c.)
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*/
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do_sql_command(conn, "SET datestyle = ISO");
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if (remoteversion >= 80400)
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do_sql_command(conn, "SET intervalstyle = postgres");
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if (remoteversion >= 90000)
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do_sql_command(conn, "SET extra_float_digits = 3");
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else
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do_sql_command(conn, "SET extra_float_digits = 2");
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}
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/*
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* Convenience subroutine to issue a non-data-returning SQL command to remote
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*/
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static void
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do_sql_command(PGconn *conn, const char *sql)
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{
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PGresult *res;
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res = PQexec(conn, sql);
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if (PQresultStatus(res) != PGRES_COMMAND_OK)
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pgfdw_report_error(ERROR, res, conn, true, sql);
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PQclear(res);
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}
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/*
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* Start remote transaction or subtransaction, if needed.
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*
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* Note that we always use at least REPEATABLE READ in the remote session.
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* This is so that, if a query initiates multiple scans of the same or
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* different foreign tables, we will get snapshot-consistent results from
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* those scans. A disadvantage is that we can't provide sane emulation of
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* READ COMMITTED behavior --- it would be nice if we had some other way to
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* control which remote queries share a snapshot.
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*/
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static void
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begin_remote_xact(ConnCacheEntry *entry)
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{
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int curlevel = GetCurrentTransactionNestLevel();
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/* Start main transaction if we haven't yet */
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if (entry->xact_depth <= 0)
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{
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const char *sql;
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elog(DEBUG3, "starting remote transaction on connection %p",
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entry->conn);
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if (IsolationIsSerializable())
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sql = "START TRANSACTION ISOLATION LEVEL SERIALIZABLE";
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else
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sql = "START TRANSACTION ISOLATION LEVEL REPEATABLE READ";
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do_sql_command(entry->conn, sql);
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entry->xact_depth = 1;
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}
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/*
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* If we're in a subtransaction, stack up savepoints to match our level.
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* This ensures we can rollback just the desired effects when a
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* subtransaction aborts.
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*/
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while (entry->xact_depth < curlevel)
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{
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char sql[64];
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snprintf(sql, sizeof(sql), "SAVEPOINT s%d", entry->xact_depth + 1);
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do_sql_command(entry->conn, sql);
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entry->xact_depth++;
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}
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}
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/*
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* Release connection reference count created by calling GetConnection.
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*/
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void
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ReleaseConnection(PGconn *conn)
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{
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/*
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* Currently, we don't actually track connection references because all
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* cleanup is managed on a transaction or subtransaction basis instead. So
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* there's nothing to do here.
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*/
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}
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/*
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* Assign a "unique" number for a cursor.
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*
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* These really only need to be unique per connection within a transaction.
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* For the moment we ignore the per-connection point and assign them across
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* all connections in the transaction, but we ask for the connection to be
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* supplied in case we want to refine that.
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*
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* Note that even if wraparound happens in a very long transaction, actual
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* collisions are highly improbable; just be sure to use %u not %d to print.
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*/
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unsigned int
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GetCursorNumber(PGconn *conn)
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{
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return ++cursor_number;
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}
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/*
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* Assign a "unique" number for a prepared statement.
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*
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* This works much like GetCursorNumber, except that we never reset the counter
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* within a session. That's because we can't be 100% sure we've gotten rid
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* of all prepared statements on all connections, and it's not really worth
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* increasing the risk of prepared-statement name collisions by resetting.
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*/
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unsigned int
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GetPrepStmtNumber(PGconn *conn)
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{
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return ++prep_stmt_number;
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}
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/*
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* Report an error we got from the remote server.
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*
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* elevel: error level to use (typically ERROR, but might be less)
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* res: PGresult containing the error
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* conn: connection we did the query on
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* clear: if true, PQclear the result (otherwise caller will handle it)
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* sql: NULL, or text of remote command we tried to execute
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*
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* Note: callers that choose not to throw ERROR for a remote error are
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* responsible for making sure that the associated ConnCacheEntry gets
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* marked with have_error = true.
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*/
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void
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pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
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bool clear, const char *sql)
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{
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/* If requested, PGresult must be released before leaving this function. */
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PG_TRY();
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{
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char *diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
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char *message_primary = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
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char *message_detail = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL);
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char *message_hint = PQresultErrorField(res, PG_DIAG_MESSAGE_HINT);
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char *message_context = PQresultErrorField(res, PG_DIAG_CONTEXT);
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int sqlstate;
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if (diag_sqlstate)
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sqlstate = MAKE_SQLSTATE(diag_sqlstate[0],
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diag_sqlstate[1],
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diag_sqlstate[2],
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diag_sqlstate[3],
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diag_sqlstate[4]);
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else
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sqlstate = ERRCODE_CONNECTION_FAILURE;
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/*
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* If we don't get a message from the PGresult, try the PGconn. This
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* is needed because for connection-level failures, PQexec may just
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* return NULL, not a PGresult at all.
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*/
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if (message_primary == NULL)
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message_primary = PQerrorMessage(conn);
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ereport(elevel,
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(errcode(sqlstate),
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message_primary ? errmsg_internal("%s", message_primary) :
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errmsg("unknown error"),
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message_detail ? errdetail_internal("%s", message_detail) : 0,
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message_hint ? errhint("%s", message_hint) : 0,
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message_context ? errcontext("%s", message_context) : 0,
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sql ? errcontext("Remote SQL command: %s", sql) : 0));
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}
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PG_CATCH();
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{
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if (clear)
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PQclear(res);
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PG_RE_THROW();
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}
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PG_END_TRY();
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if (clear)
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PQclear(res);
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}
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/*
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* pgfdw_xact_callback --- cleanup at main-transaction end.
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*/
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static void
|
|
pgfdw_xact_callback(XactEvent event, void *arg)
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{
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HASH_SEQ_STATUS scan;
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ConnCacheEntry *entry;
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|
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|
/* Quick exit if no connections were touched in this transaction. */
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if (!xact_got_connection)
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return;
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|
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/*
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* Scan all connection cache entries to find open remote transactions, and
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* close them.
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*/
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|
hash_seq_init(&scan, ConnectionHash);
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while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
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|
{
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PGresult *res;
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|
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/* Ignore cache entry if no open connection right now */
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if (entry->conn == NULL)
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continue;
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|
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/* If it has an open remote transaction, try to close it */
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if (entry->xact_depth > 0)
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{
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elog(DEBUG3, "closing remote transaction on connection %p",
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entry->conn);
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|
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switch (event)
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{
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case XACT_EVENT_PARALLEL_PRE_COMMIT:
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case XACT_EVENT_PRE_COMMIT:
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/* Commit all remote transactions during pre-commit */
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do_sql_command(entry->conn, "COMMIT TRANSACTION");
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|
|
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/*
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* If there were any errors in subtransactions, and we
|
|
* made prepared statements, do a DEALLOCATE ALL to make
|
|
* sure we get rid of all prepared statements. This is
|
|
* annoying and not terribly bulletproof, but it's
|
|
* probably not worth trying harder.
|
|
*
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|
* DEALLOCATE ALL only exists in 8.3 and later, so this
|
|
* constrains how old a server postgres_fdw can
|
|
* communicate with. We intentionally ignore errors in
|
|
* the DEALLOCATE, so that we can hobble along to some
|
|
* extent with older servers (leaking prepared statements
|
|
* as we go; but we don't really support update operations
|
|
* pre-8.3 anyway).
|
|
*/
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|
if (entry->have_prep_stmt && entry->have_error)
|
|
{
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|
res = PQexec(entry->conn, "DEALLOCATE ALL");
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|
PQclear(res);
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|
}
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|
entry->have_prep_stmt = false;
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|
entry->have_error = false;
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|
break;
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|
case XACT_EVENT_PRE_PREPARE:
|
|
|
|
/*
|
|
* We disallow remote transactions that modified anything,
|
|
* since it's not very reasonable to hold them open until
|
|
* the prepared transaction is committed. For the moment,
|
|
* throw error unconditionally; later we might allow
|
|
* read-only cases. Note that the error will cause us to
|
|
* come right back here with event == XACT_EVENT_ABORT, so
|
|
* we'll clean up the connection state at that point.
|
|
*/
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
|
|
errmsg("cannot prepare a transaction that modified remote tables")));
|
|
break;
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|
case XACT_EVENT_PARALLEL_COMMIT:
|
|
case XACT_EVENT_COMMIT:
|
|
case XACT_EVENT_PREPARE:
|
|
/* Pre-commit should have closed the open transaction */
|
|
elog(ERROR, "missed cleaning up connection during pre-commit");
|
|
break;
|
|
case XACT_EVENT_PARALLEL_ABORT:
|
|
case XACT_EVENT_ABORT:
|
|
/* Assume we might have lost track of prepared statements */
|
|
entry->have_error = true;
|
|
/* If we're aborting, abort all remote transactions too */
|
|
res = PQexec(entry->conn, "ABORT TRANSACTION");
|
|
/* Note: can't throw ERROR, it would be infinite loop */
|
|
if (PQresultStatus(res) != PGRES_COMMAND_OK)
|
|
pgfdw_report_error(WARNING, res, entry->conn, true,
|
|
"ABORT TRANSACTION");
|
|
else
|
|
{
|
|
PQclear(res);
|
|
/* As above, make sure to clear any prepared stmts */
|
|
if (entry->have_prep_stmt && entry->have_error)
|
|
{
|
|
res = PQexec(entry->conn, "DEALLOCATE ALL");
|
|
PQclear(res);
|
|
}
|
|
entry->have_prep_stmt = false;
|
|
entry->have_error = false;
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
|
|
/* Reset state to show we're out of a transaction */
|
|
entry->xact_depth = 0;
|
|
|
|
/*
|
|
* If the connection isn't in a good idle state, discard it to
|
|
* recover. Next GetConnection will open a new connection.
|
|
*/
|
|
if (PQstatus(entry->conn) != CONNECTION_OK ||
|
|
PQtransactionStatus(entry->conn) != PQTRANS_IDLE)
|
|
{
|
|
elog(DEBUG3, "discarding connection %p", entry->conn);
|
|
PQfinish(entry->conn);
|
|
entry->conn = NULL;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Regardless of the event type, we can now mark ourselves as out of the
|
|
* transaction. (Note: if we are here during PRE_COMMIT or PRE_PREPARE,
|
|
* this saves a useless scan of the hashtable during COMMIT or PREPARE.)
|
|
*/
|
|
xact_got_connection = false;
|
|
|
|
/* Also reset cursor numbering for next transaction */
|
|
cursor_number = 0;
|
|
}
|
|
|
|
/*
|
|
* pgfdw_subxact_callback --- cleanup at subtransaction end.
|
|
*/
|
|
static void
|
|
pgfdw_subxact_callback(SubXactEvent event, SubTransactionId mySubid,
|
|
SubTransactionId parentSubid, void *arg)
|
|
{
|
|
HASH_SEQ_STATUS scan;
|
|
ConnCacheEntry *entry;
|
|
int curlevel;
|
|
|
|
/* Nothing to do at subxact start, nor after commit. */
|
|
if (!(event == SUBXACT_EVENT_PRE_COMMIT_SUB ||
|
|
event == SUBXACT_EVENT_ABORT_SUB))
|
|
return;
|
|
|
|
/* Quick exit if no connections were touched in this transaction. */
|
|
if (!xact_got_connection)
|
|
return;
|
|
|
|
/*
|
|
* Scan all connection cache entries to find open remote subtransactions
|
|
* of the current level, and close them.
|
|
*/
|
|
curlevel = GetCurrentTransactionNestLevel();
|
|
hash_seq_init(&scan, ConnectionHash);
|
|
while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
|
|
{
|
|
PGresult *res;
|
|
char sql[100];
|
|
|
|
/*
|
|
* We only care about connections with open remote subtransactions of
|
|
* the current level.
|
|
*/
|
|
if (entry->conn == NULL || entry->xact_depth < curlevel)
|
|
continue;
|
|
|
|
if (entry->xact_depth > curlevel)
|
|
elog(ERROR, "missed cleaning up remote subtransaction at level %d",
|
|
entry->xact_depth);
|
|
|
|
if (event == SUBXACT_EVENT_PRE_COMMIT_SUB)
|
|
{
|
|
/* Commit all remote subtransactions during pre-commit */
|
|
snprintf(sql, sizeof(sql), "RELEASE SAVEPOINT s%d", curlevel);
|
|
do_sql_command(entry->conn, sql);
|
|
}
|
|
else
|
|
{
|
|
/* Assume we might have lost track of prepared statements */
|
|
entry->have_error = true;
|
|
/* Rollback all remote subtransactions during abort */
|
|
snprintf(sql, sizeof(sql),
|
|
"ROLLBACK TO SAVEPOINT s%d; RELEASE SAVEPOINT s%d",
|
|
curlevel, curlevel);
|
|
res = PQexec(entry->conn, sql);
|
|
if (PQresultStatus(res) != PGRES_COMMAND_OK)
|
|
pgfdw_report_error(WARNING, res, entry->conn, true, sql);
|
|
else
|
|
PQclear(res);
|
|
}
|
|
|
|
/* OK, we're outta that level of subtransaction */
|
|
entry->xact_depth--;
|
|
}
|
|
}
|