/*------------------------------------------------------------------------- * * connection.c * Connection management functions for postgres_fdw * * Portions Copyright (c) 2012-2020, PostgreSQL Global Development Group * * IDENTIFICATION * contrib/postgres_fdw/connection.c * *------------------------------------------------------------------------- */ #include "postgres.h" #include "access/htup_details.h" #include "access/xact.h" #include "catalog/pg_user_mapping.h" #include "commands/defrem.h" #include "mb/pg_wchar.h" #include "miscadmin.h" #include "pgstat.h" #include "postgres_fdw.h" #include "storage/latch.h" #include "utils/hsearch.h" #include "utils/inval.h" #include "utils/memutils.h" #include "utils/syscache.h" /* * Connection cache hash table entry * * The lookup key in this hash table is the user mapping OID. We use just one * connection per user mapping ID, which ensures that all the scans use the * same snapshot during a query. Using the user mapping OID rather than * the foreign server OID + user OID avoids creating multiple connections when * the public user mapping applies to all user OIDs. * * The "conn" pointer can be NULL if we don't currently have a live connection. * When we do have a connection, xact_depth tracks the current depth of * transactions and subtransactions open on the remote side. We need to issue * commands at the same nesting depth on the remote as we're executing at * ourselves, so that rolling back a subtransaction will kill the right * queries and not the wrong ones. */ typedef Oid ConnCacheKey; typedef struct ConnCacheEntry { ConnCacheKey key; /* hash key (must be first) */ PGconn *conn; /* connection to foreign server, or NULL */ /* Remaining fields are invalid when conn is NULL: */ int xact_depth; /* 0 = no xact open, 1 = main xact open, 2 = * one level of subxact open, etc */ bool have_prep_stmt; /* have we prepared any stmts in this xact? */ bool have_error; /* have any subxacts aborted in this xact? */ bool changing_xact_state; /* xact state change in process */ bool invalidated; /* true if reconnect is pending */ uint32 server_hashvalue; /* hash value of foreign server OID */ uint32 mapping_hashvalue; /* hash value of user mapping OID */ } ConnCacheEntry; /* * Connection cache (initialized on first use) */ static HTAB *ConnectionHash = NULL; /* for assigning cursor numbers and prepared statement numbers */ static unsigned int cursor_number = 0; static unsigned int prep_stmt_number = 0; /* tracks whether any work is needed in callback functions */ static bool xact_got_connection = false; /* prototypes of private functions */ static PGconn *connect_pg_server(ForeignServer *server, UserMapping *user); static void disconnect_pg_server(ConnCacheEntry *entry); static void check_conn_params(const char **keywords, const char **values, UserMapping *user); static void configure_remote_session(PGconn *conn); static void do_sql_command(PGconn *conn, const char *sql); static void begin_remote_xact(ConnCacheEntry *entry); static void pgfdw_xact_callback(XactEvent event, void *arg); static void pgfdw_subxact_callback(SubXactEvent event, SubTransactionId mySubid, SubTransactionId parentSubid, void *arg); static void pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue); static void pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry); static bool pgfdw_cancel_query(PGconn *conn); static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query, bool ignore_errors); static bool pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result); static bool UserMappingPasswordRequired(UserMapping *user); /* * Get a PGconn which can be used to execute queries on the remote PostgreSQL * server with the user's authorization. A new connection is established * if we don't already have a suitable one, and a transaction is opened at * the right subtransaction nesting depth if we didn't do that already. * * will_prep_stmt must be true if caller intends to create any prepared * statements. Since those don't go away automatically at transaction end * (not even on error), we need this flag to cue manual cleanup. */ PGconn * GetConnection(UserMapping *user, bool will_prep_stmt) { bool found; ConnCacheEntry *entry; ConnCacheKey key; /* First time through, initialize connection cache hashtable */ if (ConnectionHash == NULL) { HASHCTL ctl; MemSet(&ctl, 0, sizeof(ctl)); ctl.keysize = sizeof(ConnCacheKey); ctl.entrysize = sizeof(ConnCacheEntry); /* allocate ConnectionHash in the cache context */ ctl.hcxt = CacheMemoryContext; ConnectionHash = hash_create("postgres_fdw connections", 8, &ctl, HASH_ELEM | HASH_BLOBS | HASH_CONTEXT); /* * Register some callback functions that manage connection cleanup. * This should be done just once in each backend. */ RegisterXactCallback(pgfdw_xact_callback, NULL); RegisterSubXactCallback(pgfdw_subxact_callback, NULL); CacheRegisterSyscacheCallback(FOREIGNSERVEROID, pgfdw_inval_callback, (Datum) 0); CacheRegisterSyscacheCallback(USERMAPPINGOID, pgfdw_inval_callback, (Datum) 0); } /* Set flag that we did GetConnection during the current transaction */ xact_got_connection = true; /* Create hash key for the entry. Assume no pad bytes in key struct */ key = user->umid; /* * Find or create cached entry for requested connection. */ entry = hash_search(ConnectionHash, &key, HASH_ENTER, &found); if (!found) { /* * We need only clear "conn" here; remaining fields will be filled * later when "conn" is set. */ entry->conn = NULL; } /* Reject further use of connections which failed abort cleanup. */ pgfdw_reject_incomplete_xact_state_change(entry); /* * If the connection needs to be remade due to invalidation, disconnect as * soon as we're out of all transactions. */ if (entry->conn != NULL && entry->invalidated && entry->xact_depth == 0) { elog(DEBUG3, "closing connection %p for option changes to take effect", entry->conn); disconnect_pg_server(entry); } /* * We don't check the health of cached connection here, because it would * require some overhead. Broken connection will be detected when the * connection is actually used. */ /* * If cache entry doesn't have a connection, we have to establish a new * connection. (If connect_pg_server throws an error, the cache entry * will remain in a valid empty state, ie conn == NULL.) */ if (entry->conn == NULL) { ForeignServer *server = GetForeignServer(user->serverid); /* Reset all transient state fields, to be sure all are clean */ entry->xact_depth = 0; entry->have_prep_stmt = false; entry->have_error = false; entry->changing_xact_state = false; entry->invalidated = false; entry->server_hashvalue = GetSysCacheHashValue1(FOREIGNSERVEROID, ObjectIdGetDatum(server->serverid)); entry->mapping_hashvalue = GetSysCacheHashValue1(USERMAPPINGOID, ObjectIdGetDatum(user->umid)); /* Now try to make the connection */ entry->conn = connect_pg_server(server, user); elog(DEBUG3, "new postgres_fdw connection %p for server \"%s\" (user mapping oid %u, userid %u)", entry->conn, server->servername, user->umid, user->userid); } /* * Start a new transaction or subtransaction if needed. */ begin_remote_xact(entry); /* Remember if caller will prepare statements */ entry->have_prep_stmt |= will_prep_stmt; return entry->conn; } /* * Connect to remote server using specified server and user mapping properties. */ static PGconn * connect_pg_server(ForeignServer *server, UserMapping *user) { PGconn *volatile conn = NULL; /* * Use PG_TRY block to ensure closing connection on error. */ PG_TRY(); { const char **keywords; const char **values; int n; /* * Construct connection params from generic options of ForeignServer * and UserMapping. (Some of them might not be libpq options, in * which case we'll just waste a few array slots.) Add 3 extra slots * for fallback_application_name, client_encoding, end marker. */ n = list_length(server->options) + list_length(user->options) + 3; keywords = (const char **) palloc(n * sizeof(char *)); values = (const char **) palloc(n * sizeof(char *)); n = 0; n += ExtractConnectionOptions(server->options, keywords + n, values + n); n += ExtractConnectionOptions(user->options, keywords + n, values + n); /* Use "postgres_fdw" as fallback_application_name. */ keywords[n] = "fallback_application_name"; values[n] = "postgres_fdw"; n++; /* Set client_encoding so that libpq can convert encoding properly. */ keywords[n] = "client_encoding"; values[n] = GetDatabaseEncodingName(); n++; keywords[n] = values[n] = NULL; /* verify connection parameters and make connection */ check_conn_params(keywords, values, user); conn = PQconnectdbParams(keywords, values, false); if (!conn || PQstatus(conn) != CONNECTION_OK) ereport(ERROR, (errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION), errmsg("could not connect to server \"%s\"", server->servername), errdetail_internal("%s", pchomp(PQerrorMessage(conn))))); /* * Check that non-superuser has used password to establish connection; * otherwise, he's piggybacking on the postgres server's user * identity. See also dblink_security_check() in contrib/dblink * and check_conn_params. */ if (!superuser_arg(user->userid) && UserMappingPasswordRequired(user) && !PQconnectionUsedPassword(conn)) ereport(ERROR, (errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED), errmsg("password is required"), errdetail("Non-superuser cannot connect if the server does not request a password."), errhint("Target server's authentication method must be changed or password_required=false set in the user mapping attributes."))); /* Prepare new session for use */ configure_remote_session(conn); pfree(keywords); pfree(values); } PG_CATCH(); { /* Release PGconn data structure if we managed to create one */ if (conn) PQfinish(conn); PG_RE_THROW(); } PG_END_TRY(); return conn; } /* * Disconnect any open connection for a connection cache entry. */ static void disconnect_pg_server(ConnCacheEntry *entry) { if (entry->conn != NULL) { PQfinish(entry->conn); entry->conn = NULL; } } /* * Return true if the password_required is defined and false for this user * mapping, otherwise false. The mapping has been pre-validated. */ static bool UserMappingPasswordRequired(UserMapping *user) { ListCell *cell; foreach(cell, user->options) { DefElem *def = (DefElem *) lfirst(cell); if (strcmp(def->defname, "password_required") == 0) return defGetBoolean(def); } return true; } /* * For non-superusers, insist that the connstr specify a password. This * prevents a password from being picked up from .pgpass, a service file, the * environment, etc. We don't want the postgres user's passwords, * certificates, etc to be accessible to non-superusers. (See also * dblink_connstr_check in contrib/dblink.) */ static void check_conn_params(const char **keywords, const char **values, UserMapping *user) { int i; /* no check required if superuser */ if (superuser_arg(user->userid)) return; /* ok if params contain a non-empty password */ for (i = 0; keywords[i] != NULL; i++) { if (strcmp(keywords[i], "password") == 0 && values[i][0] != '\0') return; } /* ok if the superuser explicitly said so at user mapping creation time */ if (!UserMappingPasswordRequired(user)) return; ereport(ERROR, (errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED), errmsg("password is required"), errdetail("Non-superusers must provide a password in the user mapping."))); } /* * Issue SET commands to make sure remote session is configured properly. * * We do this just once at connection, assuming nothing will change the * values later. Since we'll never send volatile function calls to the * remote, there shouldn't be any way to break this assumption from our end. * It's possible to think of ways to break it at the remote end, eg making * a foreign table point to a view that includes a set_config call --- * but once you admit the possibility of a malicious view definition, * there are any number of ways to break things. */ static void configure_remote_session(PGconn *conn) { int remoteversion = PQserverVersion(conn); /* Force the search path to contain only pg_catalog (see deparse.c) */ do_sql_command(conn, "SET search_path = pg_catalog"); /* * Set remote timezone; this is basically just cosmetic, since all * transmitted and returned timestamptzs should specify a zone explicitly * anyway. However it makes the regression test outputs more predictable. * * We don't risk setting remote zone equal to ours, since the remote * server might use a different timezone database. Instead, use UTC * (quoted, because very old servers are picky about case). */ do_sql_command(conn, "SET timezone = 'UTC'"); /* * Set values needed to ensure unambiguous data output from remote. (This * logic should match what pg_dump does. See also set_transmission_modes * in postgres_fdw.c.) */ do_sql_command(conn, "SET datestyle = ISO"); if (remoteversion >= 80400) do_sql_command(conn, "SET intervalstyle = postgres"); if (remoteversion >= 90000) do_sql_command(conn, "SET extra_float_digits = 3"); else do_sql_command(conn, "SET extra_float_digits = 2"); } /* * Convenience subroutine to issue a non-data-returning SQL command to remote */ static void do_sql_command(PGconn *conn, const char *sql) { PGresult *res; if (!PQsendQuery(conn, sql)) pgfdw_report_error(ERROR, NULL, conn, false, sql); res = pgfdw_get_result(conn, sql); if (PQresultStatus(res) != PGRES_COMMAND_OK) pgfdw_report_error(ERROR, res, conn, true, sql); PQclear(res); } /* * Start remote transaction or subtransaction, if needed. * * Note that we always use at least REPEATABLE READ in the remote session. * This is so that, if a query initiates multiple scans of the same or * different foreign tables, we will get snapshot-consistent results from * those scans. A disadvantage is that we can't provide sane emulation of * READ COMMITTED behavior --- it would be nice if we had some other way to * control which remote queries share a snapshot. */ static void begin_remote_xact(ConnCacheEntry *entry) { int curlevel = GetCurrentTransactionNestLevel(); /* Start main transaction if we haven't yet */ if (entry->xact_depth <= 0) { const char *sql; elog(DEBUG3, "starting remote transaction on connection %p", entry->conn); if (IsolationIsSerializable()) sql = "START TRANSACTION ISOLATION LEVEL SERIALIZABLE"; else sql = "START TRANSACTION ISOLATION LEVEL REPEATABLE READ"; entry->changing_xact_state = true; do_sql_command(entry->conn, sql); entry->xact_depth = 1; entry->changing_xact_state = false; } /* * If we're in a subtransaction, stack up savepoints to match our level. * This ensures we can rollback just the desired effects when a * subtransaction aborts. */ while (entry->xact_depth < curlevel) { char sql[64]; snprintf(sql, sizeof(sql), "SAVEPOINT s%d", entry->xact_depth + 1); entry->changing_xact_state = true; do_sql_command(entry->conn, sql); entry->xact_depth++; entry->changing_xact_state = false; } } /* * Release connection reference count created by calling GetConnection. */ void ReleaseConnection(PGconn *conn) { /* * Currently, we don't actually track connection references because all * cleanup is managed on a transaction or subtransaction basis instead. So * there's nothing to do here. */ } /* * Assign a "unique" number for a cursor. * * These really only need to be unique per connection within a transaction. * For the moment we ignore the per-connection point and assign them across * all connections in the transaction, but we ask for the connection to be * supplied in case we want to refine that. * * Note that even if wraparound happens in a very long transaction, actual * collisions are highly improbable; just be sure to use %u not %d to print. */ unsigned int GetCursorNumber(PGconn *conn) { return ++cursor_number; } /* * Assign a "unique" number for a prepared statement. * * This works much like GetCursorNumber, except that we never reset the counter * within a session. That's because we can't be 100% sure we've gotten rid * of all prepared statements on all connections, and it's not really worth * increasing the risk of prepared-statement name collisions by resetting. */ unsigned int GetPrepStmtNumber(PGconn *conn) { return ++prep_stmt_number; } /* * Submit a query and wait for the result. * * This function is interruptible by signals. * * Caller is responsible for the error handling on the result. */ PGresult * pgfdw_exec_query(PGconn *conn, const char *query) { /* * Submit a query. Since we don't use non-blocking mode, this also can * block. But its risk is relatively small, so we ignore that for now. */ if (!PQsendQuery(conn, query)) pgfdw_report_error(ERROR, NULL, conn, false, query); /* Wait for the result. */ return pgfdw_get_result(conn, query); } /* * Wait for the result from a prior asynchronous execution function call. * * This function offers quick responsiveness by checking for any interruptions. * * This function emulates PQexec()'s behavior of returning the last result * when there are many. * * Caller is responsible for the error handling on the result. */ PGresult * pgfdw_get_result(PGconn *conn, const char *query) { PGresult *volatile last_res = NULL; /* In what follows, do not leak any PGresults on an error. */ PG_TRY(); { for (;;) { PGresult *res; while (PQisBusy(conn)) { int wc; /* Sleep until there's something to do */ wc = WaitLatchOrSocket(MyLatch, WL_LATCH_SET | WL_SOCKET_READABLE | WL_EXIT_ON_PM_DEATH, PQsocket(conn), -1L, PG_WAIT_EXTENSION); ResetLatch(MyLatch); CHECK_FOR_INTERRUPTS(); /* Data available in socket? */ if (wc & WL_SOCKET_READABLE) { if (!PQconsumeInput(conn)) pgfdw_report_error(ERROR, NULL, conn, false, query); } } res = PQgetResult(conn); if (res == NULL) break; /* query is complete */ PQclear(last_res); last_res = res; } } PG_CATCH(); { PQclear(last_res); PG_RE_THROW(); } PG_END_TRY(); return last_res; } /* * Report an error we got from the remote server. * * elevel: error level to use (typically ERROR, but might be less) * res: PGresult containing the error * conn: connection we did the query on * clear: if true, PQclear the result (otherwise caller will handle it) * sql: NULL, or text of remote command we tried to execute * * Note: callers that choose not to throw ERROR for a remote error are * responsible for making sure that the associated ConnCacheEntry gets * marked with have_error = true. */ void pgfdw_report_error(int elevel, PGresult *res, PGconn *conn, bool clear, const char *sql) { /* If requested, PGresult must be released before leaving this function. */ PG_TRY(); { char *diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE); char *message_primary = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY); char *message_detail = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL); char *message_hint = PQresultErrorField(res, PG_DIAG_MESSAGE_HINT); char *message_context = PQresultErrorField(res, PG_DIAG_CONTEXT); int sqlstate; if (diag_sqlstate) sqlstate = MAKE_SQLSTATE(diag_sqlstate[0], diag_sqlstate[1], diag_sqlstate[2], diag_sqlstate[3], diag_sqlstate[4]); else sqlstate = ERRCODE_CONNECTION_FAILURE; /* * If we don't get a message from the PGresult, try the PGconn. This * is needed because for connection-level failures, PQexec may just * return NULL, not a PGresult at all. */ if (message_primary == NULL) message_primary = pchomp(PQerrorMessage(conn)); ereport(elevel, (errcode(sqlstate), message_primary ? errmsg_internal("%s", message_primary) : errmsg("could not obtain message string for remote error"), message_detail ? errdetail_internal("%s", message_detail) : 0, message_hint ? errhint("%s", message_hint) : 0, message_context ? errcontext("%s", message_context) : 0, sql ? errcontext("remote SQL command: %s", sql) : 0)); } PG_FINALLY(); { if (clear) PQclear(res); } PG_END_TRY(); } /* * pgfdw_xact_callback --- cleanup at main-transaction end. */ static void pgfdw_xact_callback(XactEvent event, void *arg) { HASH_SEQ_STATUS scan; ConnCacheEntry *entry; /* Quick exit if no connections were touched in this transaction. */ if (!xact_got_connection) return; /* * Scan all connection cache entries to find open remote transactions, and * close them. */ hash_seq_init(&scan, ConnectionHash); while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) { PGresult *res; /* Ignore cache entry if no open connection right now */ if (entry->conn == NULL) continue; /* If it has an open remote transaction, try to close it */ if (entry->xact_depth > 0) { bool abort_cleanup_failure = false; elog(DEBUG3, "closing remote transaction on connection %p", entry->conn); switch (event) { case XACT_EVENT_PARALLEL_PRE_COMMIT: case XACT_EVENT_PRE_COMMIT: /* * If abort cleanup previously failed for this connection, * we can't issue any more commands against it. */ pgfdw_reject_incomplete_xact_state_change(entry); /* Commit all remote transactions during pre-commit */ entry->changing_xact_state = true; do_sql_command(entry->conn, "COMMIT TRANSACTION"); entry->changing_xact_state = false; /* * 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. * * 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). */ 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; case XACT_EVENT_PRE_PREPARE: /* * We disallow any remote transactions, 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 has operated on postgres_fdw foreign tables"))); break; 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: /* * Don't try to clean up the connection if we're already * in error recursion trouble. */ if (in_error_recursion_trouble()) entry->changing_xact_state = true; /* * If connection is already unsalvageable, don't touch it * further. */ if (entry->changing_xact_state) break; /* * Mark this connection as in the process of changing * transaction state. */ entry->changing_xact_state = true; /* Assume we might have lost track of prepared statements */ entry->have_error = true; /* * If a command has been submitted to the remote server by * using an asynchronous execution function, the command * might not have yet completed. Check to see if a * command is still being processed by the remote server, * and if so, request cancellation of the command. */ if (PQtransactionStatus(entry->conn) == PQTRANS_ACTIVE && !pgfdw_cancel_query(entry->conn)) { /* Unable to cancel running query. */ abort_cleanup_failure = true; } else if (!pgfdw_exec_cleanup_query(entry->conn, "ABORT TRANSACTION", false)) { /* Unable to abort remote transaction. */ abort_cleanup_failure = true; } else if (entry->have_prep_stmt && entry->have_error && !pgfdw_exec_cleanup_query(entry->conn, "DEALLOCATE ALL", true)) { /* Trouble clearing prepared statements. */ abort_cleanup_failure = true; } else { entry->have_prep_stmt = false; entry->have_error = false; } /* Disarm changing_xact_state if it all worked. */ entry->changing_xact_state = abort_cleanup_failure; 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 || entry->changing_xact_state) { elog(DEBUG3, "discarding connection %p", entry->conn); disconnect_pg_server(entry); } } /* * 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))) { 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) { /* * If abort cleanup previously failed for this connection, we * can't issue any more commands against it. */ pgfdw_reject_incomplete_xact_state_change(entry); /* Commit all remote subtransactions during pre-commit */ snprintf(sql, sizeof(sql), "RELEASE SAVEPOINT s%d", curlevel); entry->changing_xact_state = true; do_sql_command(entry->conn, sql); entry->changing_xact_state = false; } else if (in_error_recursion_trouble()) { /* * Don't try to clean up the connection if we're already in error * recursion trouble. */ entry->changing_xact_state = true; } else if (!entry->changing_xact_state) { bool abort_cleanup_failure = false; /* Remember that abort cleanup is in progress. */ entry->changing_xact_state = true; /* Assume we might have lost track of prepared statements */ entry->have_error = true; /* * If a command has been submitted to the remote server by using * an asynchronous execution function, the command might not have * yet completed. Check to see if a command is still being * processed by the remote server, and if so, request cancellation * of the command. */ if (PQtransactionStatus(entry->conn) == PQTRANS_ACTIVE && !pgfdw_cancel_query(entry->conn)) abort_cleanup_failure = true; else { /* Rollback all remote subtransactions during abort */ snprintf(sql, sizeof(sql), "ROLLBACK TO SAVEPOINT s%d; RELEASE SAVEPOINT s%d", curlevel, curlevel); if (!pgfdw_exec_cleanup_query(entry->conn, sql, false)) abort_cleanup_failure = true; } /* Disarm changing_xact_state if it all worked. */ entry->changing_xact_state = abort_cleanup_failure; } /* OK, we're outta that level of subtransaction */ entry->xact_depth--; } } /* * Connection invalidation callback function * * After a change to a pg_foreign_server or pg_user_mapping catalog entry, * mark connections depending on that entry as needing to be remade. * We can't immediately destroy them, since they might be in the midst of * a transaction, but we'll remake them at the next opportunity. * * Although most cache invalidation callbacks blow away all the related stuff * regardless of the given hashvalue, connections are expensive enough that * it's worth trying to avoid that. * * NB: We could avoid unnecessary disconnection more strictly by examining * individual option values, but it seems too much effort for the gain. */ static void pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue) { HASH_SEQ_STATUS scan; ConnCacheEntry *entry; Assert(cacheid == FOREIGNSERVEROID || cacheid == USERMAPPINGOID); /* ConnectionHash must exist already, if we're registered */ hash_seq_init(&scan, ConnectionHash); while ((entry = (ConnCacheEntry *) hash_seq_search(&scan))) { /* Ignore invalid entries */ if (entry->conn == NULL) continue; /* hashvalue == 0 means a cache reset, must clear all state */ if (hashvalue == 0 || (cacheid == FOREIGNSERVEROID && entry->server_hashvalue == hashvalue) || (cacheid == USERMAPPINGOID && entry->mapping_hashvalue == hashvalue)) entry->invalidated = true; } } /* * Raise an error if the given connection cache entry is marked as being * in the middle of an xact state change. This should be called at which no * such change is expected to be in progress; if one is found to be in * progress, it means that we aborted in the middle of a previous state change * and now don't know what the remote transaction state actually is. * Such connections can't safely be further used. Re-establishing the * connection would change the snapshot and roll back any writes already * performed, so that's not an option, either. Thus, we must abort. */ static void pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry) { HeapTuple tup; Form_pg_user_mapping umform; ForeignServer *server; /* nothing to do for inactive entries and entries of sane state */ if (entry->conn == NULL || !entry->changing_xact_state) return; /* make sure this entry is inactive */ disconnect_pg_server(entry); /* find server name to be shown in the message below */ tup = SearchSysCache1(USERMAPPINGOID, ObjectIdGetDatum(entry->key)); if (!HeapTupleIsValid(tup)) elog(ERROR, "cache lookup failed for user mapping %u", entry->key); umform = (Form_pg_user_mapping) GETSTRUCT(tup); server = GetForeignServer(umform->umserver); ReleaseSysCache(tup); ereport(ERROR, (errcode(ERRCODE_CONNECTION_EXCEPTION), errmsg("connection to server \"%s\" was lost", server->servername))); } /* * Cancel the currently-in-progress query (whose query text we do not have) * and ignore the result. Returns true if we successfully cancel the query * and discard any pending result, and false if not. */ static bool pgfdw_cancel_query(PGconn *conn) { PGcancel *cancel; char errbuf[256]; PGresult *result = NULL; TimestampTz endtime; /* * If it takes too long to cancel the query and discard the result, assume * the connection is dead. */ endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), 30000); /* * Issue cancel request. Unfortunately, there's no good way to limit the * amount of time that we might block inside PQgetCancel(). */ if ((cancel = PQgetCancel(conn))) { if (!PQcancel(cancel, errbuf, sizeof(errbuf))) { ereport(WARNING, (errcode(ERRCODE_CONNECTION_FAILURE), errmsg("could not send cancel request: %s", errbuf))); PQfreeCancel(cancel); return false; } PQfreeCancel(cancel); } /* Get and discard the result of the query. */ if (pgfdw_get_cleanup_result(conn, endtime, &result)) return false; PQclear(result); return true; } /* * Submit a query during (sub)abort cleanup and wait up to 30 seconds for the * result. If the query is executed without error, the return value is true. * If the query is executed successfully but returns an error, the return * value is true if and only if ignore_errors is set. If the query can't be * sent or times out, the return value is false. */ static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query, bool ignore_errors) { PGresult *result = NULL; TimestampTz endtime; /* * If it takes too long to execute a cleanup query, assume the connection * is dead. It's fairly likely that this is why we aborted in the first * place (e.g. statement timeout, user cancel), so the timeout shouldn't * be too long. */ endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), 30000); /* * Submit a query. Since we don't use non-blocking mode, this also can * block. But its risk is relatively small, so we ignore that for now. */ if (!PQsendQuery(conn, query)) { pgfdw_report_error(WARNING, NULL, conn, false, query); return false; } /* Get the result of the query. */ if (pgfdw_get_cleanup_result(conn, endtime, &result)) return false; /* Issue a warning if not successful. */ if (PQresultStatus(result) != PGRES_COMMAND_OK) { pgfdw_report_error(WARNING, result, conn, true, query); return ignore_errors; } PQclear(result); return true; } /* * Get, during abort cleanup, the result of a query that is in progress. This * might be a query that is being interrupted by transaction abort, or it might * be a query that was initiated as part of transaction abort to get the remote * side back to the appropriate state. * * It's not a huge problem if we throw an ERROR here, but if we get into error * recursion trouble, we'll end up slamming the connection shut, which will * necessitate failing the entire toplevel transaction even if subtransactions * were used. Try to use WARNING where we can. * * endtime is the time at which we should give up and assume the remote * side is dead. Returns true if the timeout expired, otherwise false. * Sets *result except in case of a timeout. */ static bool pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result) { volatile bool timed_out = false; PGresult *volatile last_res = NULL; /* In what follows, do not leak any PGresults on an error. */ PG_TRY(); { for (;;) { PGresult *res; while (PQisBusy(conn)) { int wc; TimestampTz now = GetCurrentTimestamp(); long secs; int microsecs; long cur_timeout; /* If timeout has expired, give up, else get sleep time. */ if (now >= endtime) { timed_out = true; goto exit; } TimestampDifference(now, endtime, &secs, µsecs); /* To protect against clock skew, limit sleep to one minute. */ cur_timeout = Min(60000, secs * USECS_PER_SEC + microsecs); /* Sleep until there's something to do */ wc = WaitLatchOrSocket(MyLatch, WL_LATCH_SET | WL_SOCKET_READABLE | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH, PQsocket(conn), cur_timeout, PG_WAIT_EXTENSION); ResetLatch(MyLatch); CHECK_FOR_INTERRUPTS(); /* Data available in socket? */ if (wc & WL_SOCKET_READABLE) { if (!PQconsumeInput(conn)) { /* connection trouble; treat the same as a timeout */ timed_out = true; goto exit; } } } res = PQgetResult(conn); if (res == NULL) break; /* query is complete */ PQclear(last_res); last_res = res; } exit: ; } PG_CATCH(); { PQclear(last_res); PG_RE_THROW(); } PG_END_TRY(); if (timed_out) PQclear(last_res); else *result = last_res; return timed_out; }