Make worker_spi sample code more complete
Make use of some GUC variables, and add SIGHUP handling to reload the config file. Patch submitted by Guillaume Lelarge. Also, report to pg_stat_activity. Per report from Marc Cousin, add setting of statement start time.
This commit is contained in:
Alvaro Herrera
parent
66c01707c6
commit
e543631f3c
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@ -1,16 +1,19 @@
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/* -------------------------------------------------------------------------
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*
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* worker_spi.c
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* Sample background worker code that demonstrates usage of a database
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* connection.
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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, create a schema and table, and summarizes
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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) 2012, PostgreSQL Global Development Group
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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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@ -33,14 +36,22 @@
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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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void _PG_init(void);
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static bool got_sigterm = false;
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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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@ -49,6 +60,11 @@ typedef struct worktable
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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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@ -61,14 +77,23 @@ worker_spi_sigterm(SIGNAL_ARGS)
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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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elog(LOG, "got sighup!");
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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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@ -77,10 +102,13 @@ initialize_worker_spi(worktable *table)
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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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@ -110,6 +138,9 @@ initialize_worker_spi(worktable *table)
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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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@ -119,6 +150,7 @@ initialize_worker_spi(worktable *table)
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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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static void
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@ -163,6 +195,9 @@ worker_spi_main(void *main_arg)
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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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@ -176,17 +211,45 @@ worker_spi_main(void *main_arg)
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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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1000L);
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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 which
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* 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 through
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* 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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@ -207,9 +270,13 @@ worker_spi_main(void *main_arg)
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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(0);
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@ -218,46 +285,66 @@ worker_spi_main(void *main_arg)
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/*
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* Entrypoint of this module.
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*
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* We register two worker processes here, to demonstrate how that can be done.
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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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worktable *table;
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unsigned int i;
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char name[20];
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/* register the worker processes. These values are common for both */
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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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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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worker.bgw_sighup = worker_spi_sighup;
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worker.bgw_sigterm = worker_spi_sigterm;
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/*
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* These values are used for the first worker.
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*
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* Note these are palloc'd. The reason this works after starting a new
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* worker process is that if we only fork, they point to valid allocated
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* memory in the child process; and if we fork and then exec, the exec'd
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* process will run this code again, and so the memory is also valid there.
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* Now fill in worker-specific data, and do the actual registrations.
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*/
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table = palloc(sizeof(worktable));
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table->schema = pstrdup("schema1");
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table->name = pstrdup("counted");
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for (i = 1; i <= worker_spi_total_workers; i++)
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{
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sprintf(name, "worker %d", i);
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worker.bgw_name = pstrdup(name);
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worker.bgw_name = "SPI worker 1";
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worker.bgw_restart_time = BGW_NEVER_RESTART;
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worker.bgw_main_arg = (void *) table;
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RegisterBackgroundWorker(&worker);
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table = palloc(sizeof(worktable));
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sprintf(name, "schema%d", i);
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table->schema = pstrdup(name);
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table->name = pstrdup("counted");
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worker.bgw_main_arg = (void *) table;
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/* Values for the second worker */
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table = palloc(sizeof(worktable));
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table->schema = pstrdup("our schema2");
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table->name = pstrdup("counted rows");
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worker.bgw_name = "SPI worker 2";
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worker.bgw_restart_time = 2;
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worker.bgw_main_arg = (void *) table;
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RegisterBackgroundWorker(&worker);
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RegisterBackgroundWorker(&worker);
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}
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}
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