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403 lines
11 KiB
C
403 lines
11 KiB
C
/* -------------------------------------------------------------------------
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*
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* worker_spi.c
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* Sample background worker code that demonstrates various coding
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* patterns: establishing a database connection; starting and committing
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* transactions; using GUC variables, and heeding SIGHUP to reread
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* the configuration file; reporting to pg_stat_activity; using the
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* process latch to sleep and exit in case of postmaster death.
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*
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* This code connects to a database, creates a schema and table, and summarizes
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* the numbers contained therein. To see it working, insert an initial value
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* with "total" type and some initial value; then insert some other rows with
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* "delta" type. Delta rows will be deleted by this worker and their values
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* aggregated into the total.
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*
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* Copyright (C) 2013, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/worker_spi/worker_spi.c
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*
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* -------------------------------------------------------------------------
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*/
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#include "postgres.h"
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/* These are always necessary for a bgworker */
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#include "miscadmin.h"
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#include "postmaster/bgworker.h"
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#include "storage/ipc.h"
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#include "storage/latch.h"
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#include "storage/lwlock.h"
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#include "storage/proc.h"
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#include "storage/shmem.h"
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/* these headers are used by this particular worker's code */
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#include "access/xact.h"
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#include "executor/spi.h"
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#include "fmgr.h"
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#include "lib/stringinfo.h"
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#include "pgstat.h"
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#include "utils/builtins.h"
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#include "utils/snapmgr.h"
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#include "tcop/utility.h"
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PG_MODULE_MAGIC;
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PG_FUNCTION_INFO_V1(worker_spi_launch);
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void _PG_init(void);
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void worker_spi_main(Datum);
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Datum worker_spi_launch(PG_FUNCTION_ARGS);
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/* flags set by signal handlers */
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static volatile sig_atomic_t got_sighup = false;
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static volatile sig_atomic_t got_sigterm = false;
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/* GUC variables */
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static int worker_spi_naptime = 10;
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static int worker_spi_total_workers = 2;
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typedef struct worktable
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{
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const char *schema;
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const char *name;
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} worktable;
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/*
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* Signal handler for SIGTERM
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* Set a flag to let the main loop to terminate, and set our latch to wake
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* it up.
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*/
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static void
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worker_spi_sigterm(SIGNAL_ARGS)
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{
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int save_errno = errno;
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got_sigterm = true;
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if (MyProc)
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SetLatch(&MyProc->procLatch);
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errno = save_errno;
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}
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/*
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* Signal handler for SIGHUP
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* Set a flag to let the main loop to reread the config file, and set
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* our latch to wake it up.
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*/
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static void
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worker_spi_sighup(SIGNAL_ARGS)
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{
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got_sighup = true;
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if (MyProc)
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SetLatch(&MyProc->procLatch);
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}
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/*
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* Initialize workspace for a worker process: create the schema if it doesn't
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* already exist.
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*/
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static void
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initialize_worker_spi(worktable *table)
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{
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int ret;
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int ntup;
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bool isnull;
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StringInfoData buf;
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SetCurrentStatementStartTimestamp();
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StartTransactionCommand();
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SPI_connect();
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PushActiveSnapshot(GetTransactionSnapshot());
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pgstat_report_activity(STATE_RUNNING, "initializing spi_worker schema");
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/* XXX could we use CREATE SCHEMA IF NOT EXISTS? */
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initStringInfo(&buf);
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appendStringInfo(&buf, "select count(*) from pg_namespace where nspname = '%s'",
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table->schema);
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ret = SPI_execute(buf.data, true, 0);
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if (ret != SPI_OK_SELECT)
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elog(FATAL, "SPI_execute failed: error code %d", ret);
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if (SPI_processed != 1)
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elog(FATAL, "not a singleton result");
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ntup = DatumGetInt64(SPI_getbinval(SPI_tuptable->vals[0],
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SPI_tuptable->tupdesc,
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1, &isnull));
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if (isnull)
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elog(FATAL, "null result");
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if (ntup == 0)
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{
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resetStringInfo(&buf);
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appendStringInfo(&buf,
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"CREATE SCHEMA \"%s\" "
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"CREATE TABLE \"%s\" ("
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" type text CHECK (type IN ('total', 'delta')), "
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" value integer)"
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"CREATE UNIQUE INDEX \"%s_unique_total\" ON \"%s\" (type) "
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"WHERE type = 'total'",
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table->schema, table->name, table->name, table->name);
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/* set statement start time */
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SetCurrentStatementStartTimestamp();
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ret = SPI_execute(buf.data, false, 0);
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if (ret != SPI_OK_UTILITY)
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elog(FATAL, "failed to create my schema");
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}
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SPI_finish();
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PopActiveSnapshot();
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CommitTransactionCommand();
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pgstat_report_activity(STATE_IDLE, NULL);
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}
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void
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worker_spi_main(Datum main_arg)
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{
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int index = DatumGetInt32(main_arg);
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worktable *table;
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StringInfoData buf;
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char name[20];
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table = palloc(sizeof(worktable));
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sprintf(name, "schema%d", index);
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table->schema = pstrdup(name);
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table->name = pstrdup("counted");
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/* Establish signal handlers before unblocking signals. */
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pqsignal(SIGHUP, worker_spi_sighup);
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pqsignal(SIGTERM, worker_spi_sigterm);
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/* We're now ready to receive signals */
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BackgroundWorkerUnblockSignals();
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/* Connect to our database */
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BackgroundWorkerInitializeConnection("postgres", NULL);
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elog(LOG, "%s initialized with %s.%s",
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MyBgworkerEntry->bgw_name, table->schema, table->name);
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initialize_worker_spi(table);
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/*
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* Quote identifiers passed to us. Note that this must be done after
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* initialize_worker_spi, because that routine assumes the names are not
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* quoted.
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*
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* Note some memory might be leaked here.
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*/
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table->schema = quote_identifier(table->schema);
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table->name = quote_identifier(table->name);
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initStringInfo(&buf);
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appendStringInfo(&buf,
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"WITH deleted AS (DELETE "
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"FROM %s.%s "
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"WHERE type = 'delta' RETURNING value), "
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"total AS (SELECT coalesce(sum(value), 0) as sum "
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"FROM deleted) "
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"UPDATE %s.%s "
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"SET value = %s.value + total.sum "
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"FROM total WHERE type = 'total' "
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"RETURNING %s.value",
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table->schema, table->name,
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table->schema, table->name,
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table->name,
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table->name);
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/*
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* Main loop: do this until the SIGTERM handler tells us to terminate
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*/
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while (!got_sigterm)
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{
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int ret;
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int rc;
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/*
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* Background workers mustn't call usleep() or any direct equivalent:
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* instead, they may wait on their process latch, which sleeps as
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* necessary, but is awakened if postmaster dies. That way the
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* background process goes away immediately in an emergency.
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*/
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rc = WaitLatch(&MyProc->procLatch,
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WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
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worker_spi_naptime * 1000L);
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ResetLatch(&MyProc->procLatch);
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/* emergency bailout if postmaster has died */
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if (rc & WL_POSTMASTER_DEATH)
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proc_exit(1);
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/*
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* In case of a SIGHUP, just reload the configuration.
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*/
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if (got_sighup)
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{
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got_sighup = false;
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ProcessConfigFile(PGC_SIGHUP);
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}
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/*
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* Start a transaction on which we can run queries. Note that each
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* StartTransactionCommand() call should be preceded by a
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* SetCurrentStatementStartTimestamp() call, which sets both the time
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* for the statement we're about the run, and also the transaction
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* start time. Also, each other query sent to SPI should probably be
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* preceded by SetCurrentStatementStartTimestamp(), so that statement
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* start time is always up to date.
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*
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* The SPI_connect() call lets us run queries through the SPI manager,
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* and the PushActiveSnapshot() call creates an "active" snapshot
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* which is necessary for queries to have MVCC data to work on.
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*
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* The pgstat_report_activity() call makes our activity visible
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* through the pgstat views.
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*/
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SetCurrentStatementStartTimestamp();
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StartTransactionCommand();
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SPI_connect();
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PushActiveSnapshot(GetTransactionSnapshot());
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pgstat_report_activity(STATE_RUNNING, buf.data);
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/* We can now execute queries via SPI */
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ret = SPI_execute(buf.data, false, 0);
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if (ret != SPI_OK_UPDATE_RETURNING)
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elog(FATAL, "cannot select from table %s.%s: error code %d",
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table->schema, table->name, ret);
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if (SPI_processed > 0)
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{
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bool isnull;
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int32 val;
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val = DatumGetInt32(SPI_getbinval(SPI_tuptable->vals[0],
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SPI_tuptable->tupdesc,
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1, &isnull));
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if (!isnull)
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elog(LOG, "%s: count in %s.%s is now %d",
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MyBgworkerEntry->bgw_name,
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table->schema, table->name, val);
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}
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/*
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* And finish our transaction.
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*/
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SPI_finish();
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PopActiveSnapshot();
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CommitTransactionCommand();
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pgstat_report_activity(STATE_IDLE, NULL);
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}
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proc_exit(1);
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}
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/*
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* Entrypoint of this module.
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*
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* We register more than one worker process here, to demonstrate how that can
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* be done.
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*/
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void
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_PG_init(void)
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{
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BackgroundWorker worker;
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unsigned int i;
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/* get the configuration */
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DefineCustomIntVariable("worker_spi.naptime",
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"Duration between each check (in seconds).",
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NULL,
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&worker_spi_naptime,
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10,
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1,
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INT_MAX,
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PGC_SIGHUP,
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0,
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NULL,
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NULL,
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NULL);
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if (!process_shared_preload_libraries_in_progress)
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return;
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DefineCustomIntVariable("worker_spi.total_workers",
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"Number of workers.",
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NULL,
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&worker_spi_total_workers,
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2,
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1,
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100,
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PGC_POSTMASTER,
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0,
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NULL,
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NULL,
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NULL);
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/* set up common data for all our workers */
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worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
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BGWORKER_BACKEND_DATABASE_CONNECTION;
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worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
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worker.bgw_restart_time = BGW_NEVER_RESTART;
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worker.bgw_main = worker_spi_main;
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/*
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* Now fill in worker-specific data, and do the actual registrations.
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*/
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for (i = 1; i <= worker_spi_total_workers; i++)
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{
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snprintf(worker.bgw_name, BGW_MAXLEN, "worker %d", i);
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worker.bgw_main_arg = Int32GetDatum(i);
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RegisterBackgroundWorker(&worker);
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}
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}
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/*
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* Dynamically launch an SPI worker.
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*/
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Datum
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worker_spi_launch(PG_FUNCTION_ARGS)
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{
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int32 i = PG_GETARG_INT32(0);
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BackgroundWorker worker;
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BackgroundWorkerHandle *handle;
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BgwHandleStatus status;
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pid_t pid;
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worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
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BGWORKER_BACKEND_DATABASE_CONNECTION;
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worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
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worker.bgw_restart_time = BGW_NEVER_RESTART;
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worker.bgw_main = NULL; /* new worker might not have library loaded */
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sprintf(worker.bgw_library_name, "worker_spi");
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sprintf(worker.bgw_function_name, "worker_spi_main");
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snprintf(worker.bgw_name, BGW_MAXLEN, "worker %d", i);
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worker.bgw_main_arg = Int32GetDatum(i);
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/* set bgw_notify_pid so that we can use WaitForBackgroundWorkerStartup */
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worker.bgw_notify_pid = MyProcPid;
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if (!RegisterDynamicBackgroundWorker(&worker, &handle))
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PG_RETURN_NULL();
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status = WaitForBackgroundWorkerStartup(handle, &pid);
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if (status == BGWH_STOPPED)
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ereport(ERROR,
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(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
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errmsg("could not start background process"),
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errhint("More details may be available in the server log.")));
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if (status == BGWH_POSTMASTER_DIED)
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ereport(ERROR,
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(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
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errmsg("cannot start background processes without postmaster"),
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errhint("Kill all remaining database processes and restart the database.")));
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Assert(status == BGWH_STARTED);
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PG_RETURN_INT32(pid);
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}
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