/* * config_log.c * * PostgreSQL extension with custom background worker to monitor * and record changes to postgresql.conf (experimental) * * NOTES: * - custom background workers are available from PostgreSQL 9.3 * - the background worker API is not fully finalized and * may change before final release (see also note in '_PG_init()') * * Written by Ian Barwick * barwick@gmail.com * * Copyright 2013 Ian Barwick. This program is Free * Software; see the README.md file for the license conditions. */ #include "postgres.h" /* Following are required for all bgworker */ #include "miscadmin.h" #include "postmaster/bgworker.h" #include "storage/ipc.h" #include "storage/latch.h" #include "storage/lwlock.h" #include "storage/proc.h" #include "storage/shmem.h" /* these headers are used by this particular worker's code */ #include "access/xact.h" #include "executor/spi.h" #include "fmgr.h" #include "lib/stringinfo.h" #include "pgstat.h" #include "utils/snapmgr.h" #include "tcop/utility.h" PG_MODULE_MAGIC; void _PG_init(void); /* flags set by signal handlers */ static volatile sig_atomic_t got_sighup = false; static volatile sig_atomic_t got_sigterm = false; /* GUC variables */ static char * config_log_database = NULL; static char * config_log_schema = NULL; typedef struct config_log_objects { const char *table_name; const char *function_name; } config_log_objects; config_log_objects *initialize_objects(void); static void execute_pg_settings_logger(config_log_objects *objects); static void log_info(char *msg); static void config_log_sigterm(SIGNAL_ARGS) { int save_errno = errno; got_sigterm = true; if (MyProc) { SetLatch(&MyProc->procLatch); } errno = save_errno; } static void config_log_sighup(SIGNAL_ARGS) { log_info("received sighup"); got_sighup = true; if (MyProc) { SetLatch(&MyProc->procLatch); } } static void log_info(char *msg) { ereport(LOG, (errmsg("%s: %s", MyBgworkerEntry->bgw_name, msg ))); } /* * Initialize objects * */ config_log_objects * initialize_objects(void) { config_log_objects *objects; int ret; int ntup; bool isnull; StringInfoData buf; objects = palloc(sizeof(config_log_objects)); objects->table_name = pstrdup("pg_settings_log"); objects->function_name = pstrdup("pg_settings_logger"); SetCurrentStatementStartTimestamp(); StartTransactionCommand(); SPI_connect(); PushActiveSnapshot(GetTransactionSnapshot()); pgstat_report_activity(STATE_RUNNING, "Verifying config log objects"); initStringInfo(&buf); appendStringInfo( &buf, "SELECT COUNT(*)\ FROM information_schema.tables\ WHERE table_schema='%s'\ AND table_name ='%s'\ AND table_type='BASE TABLE'", config_log_schema, objects->table_name ); ret = SPI_execute(buf.data, true, 0); if (ret != SPI_OK_SELECT) { ereport(FATAL, (errmsg("SPI_execute failed: SPI error code %d", ret) )); } /* This should never happen */ if (SPI_processed != 1) { elog(FATAL, "not a singleton result"); } ntup = DatumGetInt32(SPI_getbinval(SPI_tuptable->vals[0], SPI_tuptable->tupdesc, 1, &isnull)); /* This should never happen */ if (isnull) { elog(FATAL, "null result"); } if (ntup == 0) { ereport(FATAL, ( errmsg("Expected config log table '%s.%s' not found", config_log_schema, objects->table_name), errhint("Ensure superuser search_path includes the schema used by config_log; " "check config_log.* GUC settings") )); } /* check function pg_settings_logger() exists */ resetStringInfo(&buf); appendStringInfo( &buf, "SELECT COUNT(*) FROM pg_catalog.pg_proc p \ INNER JOIN pg_catalog.pg_namespace n ON n.oid = p.pronamespace \ WHERE p.proname='%s' \ AND n.nspname='%s' \ AND p.pronargs = 0", objects->function_name, config_log_schema ); ret = SPI_execute(buf.data, true, 0); if (ret != SPI_OK_SELECT) { ereport(FATAL, (errmsg("SPI_execute failed: SPI error code %d", ret) )); } if (SPI_processed != 1) { elog(FATAL, "not a singleton result"); } ntup = DatumGetInt32(SPI_getbinval(SPI_tuptable->vals[0], SPI_tuptable->tupdesc, 1, &isnull)); if (isnull) { elog(FATAL, "null result"); } if (ntup == 0) { ereport(FATAL, ( errmsg("Expected config log function '%s.%s' not found", config_log_schema, objects->function_name), errhint("Ensure superuser search_path includes the schema used by config_log; " "check config_log.* GUC settings") )); } SPI_finish(); PopActiveSnapshot(); CommitTransactionCommand(); pgstat_report_activity(STATE_IDLE, NULL); log_info("initialized, database objects validated"); /* execute pg_settings_logger() here to catch any settings which have changed after server restart */ execute_pg_settings_logger(objects); return objects; } static void execute_pg_settings_logger(config_log_objects *objects) { int ret; bool isnull; StringInfoData buf; SetCurrentStatementStartTimestamp(); StartTransactionCommand(); SPI_connect(); PushActiveSnapshot(GetTransactionSnapshot()); pgstat_report_activity(STATE_RUNNING, "executing configuration logger function"); initStringInfo(&buf); appendStringInfo( &buf, "SELECT %s.%s()", config_log_schema, objects->function_name ); ret = SPI_execute(buf.data, false, 0); if (ret != SPI_OK_SELECT) { elog(FATAL, "SPI_execute failed: error code %d", ret); } if (SPI_processed != 1) { elog(FATAL, "not a singleton result"); } log_info("pg_settings_logger() executed"); if(DatumGetBool(SPI_getbinval(SPI_tuptable->vals[0], SPI_tuptable->tupdesc, 1, &isnull))) { log_info("Configuration changes recorded"); } else { log_info("No configuration changes detected"); } SPI_finish(); PopActiveSnapshot(); CommitTransactionCommand(); pgstat_report_activity(STATE_IDLE, NULL); } static void config_log_main(Datum main_arg) { config_log_objects *objects; pqsignal(SIGTERM, config_log_sigterm); pqsignal(SIGHUP, config_log_sighup); /* We're now ready to receive signals */ BackgroundWorkerUnblockSignals(); /* Connect to database */ BackgroundWorkerInitializeConnection(config_log_database, NULL); /* Verify expected objects exist */ objects = initialize_objects(); while (!got_sigterm) { int rc; rc = WaitLatch(&MyProc->procLatch, WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH, 100000L); ResetLatch(&MyProc->procLatch); /* emergency bailout if postmaster has died */ if (rc & WL_POSTMASTER_DEATH) proc_exit(1); /* * In case of a SIGHUP, just reload the configuration. */ if (got_sighup) { got_sighup = false; ProcessConfigFile(PGC_SIGHUP); execute_pg_settings_logger(objects); } } proc_exit(0); } /* * Entrypoint of this module. */ void _PG_init(void) { BackgroundWorker worker; /* get GUC settings, if available */ DefineCustomStringVariable( "config_log.database", "Database used for config_log", "Database used to store config_log records (default: postgres).", &config_log_database, "postgres", PGC_POSTMASTER, 0, NULL, NULL, NULL ); DefineCustomStringVariable( "config_log.schema", "Schema used for config_log", "Schema used to store config_log records (default: public).", &config_log_schema, "public", PGC_POSTMASTER, 0, NULL, NULL, NULL ); /* register the worker processes */ worker.bgw_flags = BGWORKER_SHMEM_ACCESS | BGWORKER_BACKEND_DATABASE_CONNECTION; worker.bgw_start_time = BgWorkerStart_RecoveryFinished; worker.bgw_main = config_log_main; worker.bgw_restart_time = 1; worker.bgw_main_arg = (Datum) 0; /* this value is shown in the process list */ snprintf(worker.bgw_name, BGW_MAXLEN, "config_log"); RegisterBackgroundWorker(&worker); }