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Commite543631

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Make worker_spi sample code more complete
Make use of some GUC variables, and add SIGHUP handling to reloadthe config file. Patch submitted by Guillaume Lelarge.Also, report to pg_stat_activity. Per report from Marc Cousin, addsetting of statement start time.
1 parent66c0170 commite543631

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1 file changed

+120
-33
lines changed

1 file changed

+120
-33
lines changed

‎contrib/worker_spi/worker_spi.c‎

Lines changed: 120 additions & 33 deletions
Original file line numberDiff line numberDiff line change
@@ -1,16 +1,19 @@
11
/* -------------------------------------------------------------------------
22
*
33
* worker_spi.c
4-
*Sample background worker code that demonstrates usage of a database
5-
*connection.
4+
*Sample background worker code that demonstrates various coding
5+
*patterns: establishing a database connection; starting and committing
6+
*transactions; using GUC variables, and heeding SIGHUP to reread
7+
*the configuration file; reporting to pg_stat_activity; using the
8+
*process latch to sleep and exit in case of postmaster death.
69
*
7-
* This code connects to a database,create a schema and table, and summarizes
10+
* This code connects to a database,creates a schema and table, and summarizes
811
* the numbers contained therein. To see it working, insert an initial value
912
* with "total" type and some initial value; then insert some other rows with
1013
* "delta" type. Delta rows will be deleted by this worker and their values
1114
* aggregated into the total.
1215
*
13-
* Copyright (C)2012, PostgreSQL Global Development Group
16+
* Copyright (C)2013, PostgreSQL Global Development Group
1417
*
1518
* IDENTIFICATION
1619
*contrib/worker_spi/worker_spi.c
@@ -33,14 +36,22 @@
3336
#include"executor/spi.h"
3437
#include"fmgr.h"
3538
#include"lib/stringinfo.h"
39+
#include"pgstat.h"
3640
#include"utils/builtins.h"
3741
#include"utils/snapmgr.h"
42+
#include"tcop/utility.h"
3843

3944
PG_MODULE_MAGIC;
4045

4146
void_PG_init(void);
4247

43-
staticboolgot_sigterm= false;
48+
/* flags set by signal handlers */
49+
staticvolatilesig_atomic_tgot_sighup= false;
50+
staticvolatilesig_atomic_tgot_sigterm= false;
51+
52+
/* GUC variables */
53+
staticintworker_spi_naptime=10;
54+
staticintworker_spi_total_workers=2;
4455

4556

4657
typedefstructworktable
@@ -49,6 +60,11 @@ typedef struct worktable
4960
constchar*name;
5061
}worktable;
5162

63+
/*
64+
* Signal handler for SIGTERM
65+
* Set a flag to let the main loop to terminate, and set our latch to wake
66+
* it up.
67+
*/
5268
staticvoid
5369
worker_spi_sigterm(SIGNAL_ARGS)
5470
{
@@ -61,14 +77,23 @@ worker_spi_sigterm(SIGNAL_ARGS)
6177
errno=save_errno;
6278
}
6379

80+
/*
81+
* Signal handler for SIGHUP
82+
* Set a flag to let the main loop to reread the config file, and set
83+
* our latch to wake it up.
84+
*/
6485
staticvoid
6586
worker_spi_sighup(SIGNAL_ARGS)
6687
{
67-
elog(LOG,"got sighup!");
88+
got_sighup= true;
6889
if (MyProc)
6990
SetLatch(&MyProc->procLatch);
7091
}
7192

93+
/*
94+
* Initialize workspace for a worker process: create the schema if it doesn't
95+
* already exist.
96+
*/
7297
staticvoid
7398
initialize_worker_spi(worktable*table)
7499
{
@@ -77,10 +102,13 @@ initialize_worker_spi(worktable *table)
77102
boolisnull;
78103
StringInfoDatabuf;
79104

105+
SetCurrentStatementStartTimestamp();
80106
StartTransactionCommand();
81107
SPI_connect();
82108
PushActiveSnapshot(GetTransactionSnapshot());
109+
pgstat_report_activity(STATE_RUNNING,"initializing spi_worker schema");
83110

111+
/* XXX could we use CREATE SCHEMA IF NOT EXISTS? */
84112
initStringInfo(&buf);
85113
appendStringInfo(&buf,"select count(*) from pg_namespace where nspname = '%s'",
86114
table->schema);
@@ -110,6 +138,9 @@ initialize_worker_spi(worktable *table)
110138
"WHERE type = 'total'",
111139
table->schema,table->name,table->name,table->name);
112140

141+
/* set statement start time */
142+
SetCurrentStatementStartTimestamp();
143+
113144
ret=SPI_execute(buf.data, false,0);
114145

115146
if (ret!=SPI_OK_UTILITY)
@@ -119,6 +150,7 @@ initialize_worker_spi(worktable *table)
119150
SPI_finish();
120151
PopActiveSnapshot();
121152
CommitTransactionCommand();
153+
pgstat_report_activity(STATE_IDLE,NULL);
122154
}
123155

124156
staticvoid
@@ -163,6 +195,9 @@ worker_spi_main(void *main_arg)
163195
table->name,
164196
table->name);
165197

198+
/*
199+
* Main loop: do this until the SIGTERM handler tells us to terminate
200+
*/
166201
while (!got_sigterm)
167202
{
168203
intret;
@@ -176,17 +211,45 @@ worker_spi_main(void *main_arg)
176211
*/
177212
rc=WaitLatch(&MyProc->procLatch,
178213
WL_LATCH_SET |WL_TIMEOUT |WL_POSTMASTER_DEATH,
179-
1000L);
214+
worker_spi_naptime*1000L);
180215
ResetLatch(&MyProc->procLatch);
181216

182217
/* emergency bailout if postmaster has died */
183218
if (rc&WL_POSTMASTER_DEATH)
184219
proc_exit(1);
185220

221+
/*
222+
* In case of a SIGHUP, just reload the configuration.
223+
*/
224+
if (got_sighup)
225+
{
226+
got_sighup= false;
227+
ProcessConfigFile(PGC_SIGHUP);
228+
}
229+
230+
/*
231+
* Start a transaction on which we can run queries. Note that each
232+
* StartTransactionCommand() call should be preceded by a
233+
* SetCurrentStatementStartTimestamp() call, which sets both the time
234+
* for the statement we're about the run, and also the transaction
235+
* start time. Also, each other query sent to SPI should probably be
236+
* preceded by SetCurrentStatementStartTimestamp(), so that statement
237+
* start time is always up to date.
238+
*
239+
* The SPI_connect() call lets us run queries through the SPI manager,
240+
* and the PushActiveSnapshot() call creates an "active" snapshot which
241+
* is necessary for queries to have MVCC data to work on.
242+
*
243+
* The pgstat_report_activity() call makes our activity visible through
244+
* the pgstat views.
245+
*/
246+
SetCurrentStatementStartTimestamp();
186247
StartTransactionCommand();
187248
SPI_connect();
188249
PushActiveSnapshot(GetTransactionSnapshot());
250+
pgstat_report_activity(STATE_RUNNING,buf.data);
189251

252+
/* We can now execute queries via SPI */
190253
ret=SPI_execute(buf.data, false,0);
191254

192255
if (ret!=SPI_OK_UPDATE_RETURNING)
@@ -207,9 +270,13 @@ worker_spi_main(void *main_arg)
207270
table->schema,table->name,val);
208271
}
209272

273+
/*
274+
* And finish our transaction.
275+
*/
210276
SPI_finish();
211277
PopActiveSnapshot();
212278
CommitTransactionCommand();
279+
pgstat_report_activity(STATE_IDLE,NULL);
213280
}
214281

215282
proc_exit(0);
@@ -218,46 +285,66 @@ worker_spi_main(void *main_arg)
218285
/*
219286
* Entrypoint of this module.
220287
*
221-
* We register two worker processes here, to demonstrate how that can be done.
288+
* We register more than one worker process here, to demonstrate how that can
289+
* be done.
222290
*/
223291
void
224292
_PG_init(void)
225293
{
226294
BackgroundWorkerworker;
227295
worktable*table;
228-
229-
/* register the worker processes. These values are common for both */
296+
unsignedinti;
297+
charname[20];
298+
299+
/* get the configuration */
300+
DefineCustomIntVariable("worker_spi.naptime",
301+
"Duration between each check (in seconds).",
302+
NULL,
303+
&worker_spi_naptime,
304+
10,
305+
1,
306+
INT_MAX,
307+
PGC_SIGHUP,
308+
0,
309+
NULL,
310+
NULL,
311+
NULL);
312+
DefineCustomIntVariable("worker_spi.total_workers",
313+
"Number of workers.",
314+
NULL,
315+
&worker_spi_total_workers,
316+
2,
317+
1,
318+
100,
319+
PGC_POSTMASTER,
320+
0,
321+
NULL,
322+
NULL,
323+
NULL);
324+
325+
/* set up common data for all our workers */
230326
worker.bgw_flags=BGWORKER_SHMEM_ACCESS |
231327
BGWORKER_BACKEND_DATABASE_CONNECTION;
232328
worker.bgw_start_time=BgWorkerStart_RecoveryFinished;
329+
worker.bgw_restart_time=BGW_NEVER_RESTART;
233330
worker.bgw_main=worker_spi_main;
234331
worker.bgw_sighup=worker_spi_sighup;
235332
worker.bgw_sigterm=worker_spi_sigterm;
236333

237334
/*
238-
* These values are used for the first worker.
239-
*
240-
* Note these are palloc'd. The reason this works after starting a new
241-
* worker process is that if we only fork, they point to valid allocated
242-
* memory in the child process; and if we fork and then exec, the exec'd
243-
* process will run this code again, and so the memory is also valid there.
335+
* Now fill in worker-specific data, and do the actual registrations.
244336
*/
245-
table=palloc(sizeof(worktable));
246-
table->schema=pstrdup("schema1");
247-
table->name=pstrdup("counted");
337+
for (i=1;i <=worker_spi_total_workers;i++)
338+
{
339+
sprintf(name,"worker %d",i);
340+
worker.bgw_name=pstrdup(name);
248341

249-
worker.bgw_name="SPI worker 1";
250-
worker.bgw_restart_time=BGW_NEVER_RESTART;
251-
worker.bgw_main_arg= (void*)table;
252-
RegisterBackgroundWorker(&worker);
253-
254-
/* Values for the second worker */
255-
table=palloc(sizeof(worktable));
256-
table->schema=pstrdup("our schema2");
257-
table->name=pstrdup("counted rows");
258-
259-
worker.bgw_name="SPI worker 2";
260-
worker.bgw_restart_time=2;
261-
worker.bgw_main_arg= (void*)table;
262-
RegisterBackgroundWorker(&worker);
342+
table=palloc(sizeof(worktable));
343+
sprintf(name,"schema%d",i);
344+
table->schema=pstrdup(name);
345+
table->name=pstrdup("counted");
346+
worker.bgw_main_arg= (void*)table;
347+
348+
RegisterBackgroundWorker(&worker);
349+
}
263350
}

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