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Diffstat (limited to 'contrib/postgres_fdw/connection.c')
| -rw-r--r-- | contrib/postgres_fdw/connection.c | 1271 |
1 files changed, 1271 insertions, 0 deletions
diff --git a/contrib/postgres_fdw/connection.c b/contrib/postgres_fdw/connection.c new file mode 100644 index 0000000..512bdfb --- /dev/null +++ b/contrib/postgres_fdw/connection.c @@ -0,0 +1,1271 @@ +/*------------------------------------------------------------------------- + * + * 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/fd.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 the set of connection parameters */ + check_conn_params(keywords, values, user); + + /* + * We must obey fd.c's limit on non-virtual file descriptors. Assume + * that a PGconn represents one long-lived FD. (Doing this here also + * ensures that VFDs are closed if needed to make room.) + */ + if (!AcquireExternalFD()) + { +#ifndef WIN32 /* can't write #if within ereport() macro */ + ereport(ERROR, + (errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION), + errmsg("could not connect to server \"%s\"", + server->servername), + errdetail("There are too many open files on the local server."), + errhint("Raise the server's max_files_per_process and/or \"ulimit -n\" limits."))); +#else + ereport(ERROR, + (errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION), + errmsg("could not connect to server \"%s\"", + server->servername), + errdetail("There are too many open files on the local server."), + errhint("Raise the server's max_files_per_process setting."))); +#endif + } + + /* OK to make connection */ + conn = PQconnectdbParams(keywords, values, false); + + if (!conn) + ReleaseExternalFD(); /* because the PG_CATCH block won't */ + + 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); + ReleaseExternalFD(); + } + 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; + ReleaseExternalFD(); + } +} + +/* + * 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. + * + * This runs just late enough that it must not enter user-defined code + * locally. (Entering such code on the remote side is fine. Its remote + * COMMIT TRANSACTION may run deferred triggers.) + */ +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 or it is marked as + * invalid, then 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 || + entry->invalidated) + { + 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, + * close connections depending on that entry immediately if current transaction + * has not used those connections yet. Otherwise, mark those connections as + * invalid and then make pgfdw_xact_callback() close them at the end of current + * transaction, since they cannot be closed in the midst of the transaction + * using them. Closed connections will be remade at the next opportunity if + * necessary. + * + * 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)) + { + /* + * Close the connection immediately if it's not used yet in this + * transaction. Otherwise mark it as invalid so that + * pgfdw_xact_callback() can close it at the end of this + * transaction. + */ + if (entry->xact_depth == 0) + { + elog(DEBUG3, "discarding connection %p", entry->conn); + disconnect_pg_server(entry); + } + else + 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 cur_timeout; + + /* If timeout has expired, give up, else get sleep time. */ + cur_timeout = TimestampDifferenceMilliseconds(now, endtime); + if (cur_timeout <= 0) + { + timed_out = true; + goto exit; + } + + /* 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; +} |