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Allow background workers to be started dynamically.

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There is a new API, RegisterDynamicBackgroundWorker, which allows
an ordinary user backend to register a new background writer during
normal running.  This means that it's no longer necessary for all
background workers to be registered during processing of
shared_preload_libraries, although the option of registering workers
at that time remains available.

When a background worker exits and will not be restarted, the
slot previously used by that background worker is automatically
released and becomes available for reuse.  Slots used by background
workers that are configured for automatic restart can't (yet) be
released without shutting down the system.

This commit adds a new source file, bgworker.c, and moves some
of the existing control logic for background workers there.
Previously, there was little enough logic that it made sense to
keep everything in postmaster.c, but not any more.

This commit also makes the worker_spi contrib module into an
extension and adds a new function, worker_spi_launch, which can
be used to demonstrate the new facility.
This commit is contained in:
Robert Haas
2013-07-16 13:02:15 -04:00
parent 233bfe0673
commit 7f7485a0cd
13 changed files with 710 additions and 209 deletions
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66
contrib/worker_spi/worker_spi.c
View File

@ -42,8 +42,11 @@
#include "tcop/utility.h"
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(worker_spi_launch);
void _PG_init(void);
void worker_spi_main(Datum);
Datum worker_spi_launch(PG_FUNCTION_ARGS);
/* flags set by signal handlers */
static volatile sig_atomic_t got_sighup = false;
@ -153,11 +156,22 @@ initialize_worker_spi(worktable *table)
pgstat_report_activity(STATE_IDLE, NULL);
}
static void
worker_spi_main(void *main_arg)
void
worker_spi_main(Datum main_arg)
{
worktable *table = (worktable *) main_arg;
int index = DatumGetInt32(main_arg);
worktable *table;
StringInfoData buf;
char name[20];
table = palloc(sizeof(worktable));
sprintf(name, "schema%d", index);
table->schema = pstrdup(name);
table->name = pstrdup("counted");
/* Establish signal handlers before unblocking signals. */
pqsignal(SIGHUP, worker_spi_sighup);
pqsignal(SIGTERM, worker_spi_sigterm);
/* We're now ready to receive signals */
BackgroundWorkerUnblockSignals();
@ -279,7 +293,7 @@ worker_spi_main(void *main_arg)
pgstat_report_activity(STATE_IDLE, NULL);
}
proc_exit(0);
proc_exit(1);
}
/*
@ -292,9 +306,7 @@ void
_PG_init(void)
{
BackgroundWorker worker;
worktable *table;
unsigned int i;
char name[20];
/* get the configuration */
DefineCustomIntVariable("worker_spi.naptime",
@ -309,6 +321,10 @@ _PG_init(void)
NULL,
NULL,
NULL);
if (!process_shared_preload_libraries_in_progress)
return;
DefineCustomIntVariable("worker_spi.total_workers",
"Number of workers.",
NULL,
@ -328,23 +344,41 @@ _PG_init(void)
worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
worker.bgw_restart_time = BGW_NEVER_RESTART;
worker.bgw_main = worker_spi_main;
worker.bgw_sighup = worker_spi_sighup;
worker.bgw_sigterm = worker_spi_sigterm;
worker.bgw_sighup = NULL;
worker.bgw_sigterm = NULL;
/*
* Now fill in worker-specific data, and do the actual registrations.
*/
for (i = 1; i <= worker_spi_total_workers; i++)
{
sprintf(name, "worker %d", i);
worker.bgw_name = pstrdup(name);
table = palloc(sizeof(worktable));
sprintf(name, "schema%d", i);
table->schema = pstrdup(name);
table->name = pstrdup("counted");
worker.bgw_main_arg = (void *) table;
snprintf(worker.bgw_name, BGW_MAXLEN, "worker %d", i);
worker.bgw_main_arg = Int32GetDatum(i);
RegisterBackgroundWorker(&worker);
}
}
/*
* Dynamically launch an SPI worker.
*/
Datum
worker_spi_launch(PG_FUNCTION_ARGS)
{
int32 i = PG_GETARG_INT32(0);
BackgroundWorker worker;
worker.bgw_flags = BGWORKER_SHMEM_ACCESS |
BGWORKER_BACKEND_DATABASE_CONNECTION;
worker.bgw_start_time = BgWorkerStart_RecoveryFinished;
worker.bgw_restart_time = BGW_NEVER_RESTART;
worker.bgw_main = NULL; /* new worker might not have library loaded */
sprintf(worker.bgw_library_name, "worker_spi");
sprintf(worker.bgw_function_name, "worker_spi_main");
worker.bgw_sighup = NULL; /* new worker might not have library loaded */
worker.bgw_sigterm = NULL; /* new worker might not have library loaded */
snprintf(worker.bgw_name, BGW_MAXLEN, "worker %d", i);
worker.bgw_main_arg = Int32GetDatum(i);
PG_RETURN_BOOL(RegisterDynamicBackgroundWorker(&worker));
}