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Per discussion on pgsql-hackers, these aren't really needed. Interim versions of the background worker patch had the worker starting with signals already unblocked, which would have made this necessary. But the final version does not, so we don't really need it; and it doesn't work well with the new facility for starting dynamic background workers, so just rip it out. Also per discussion on pgsql-hackers, back-patch this change to 9.3. It's best to get the API break out of the way before we do an official release of this facility, to avoid more pain for extension authors later.
381 lines
9.9 KiB
C
381 lines
9.9 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 = 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(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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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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PG_RETURN_BOOL(RegisterDynamicBackgroundWorker(&worker));
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}
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