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Commitc63bc32

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Fix up gcc warnings, improve comments.
1 parent2da3742 commitc63bc32

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1 file changed

+50
-30
lines changed

1 file changed

+50
-30
lines changed

‎src/backend/commands/vacuum.c‎

Lines changed: 50 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@
1313
*
1414
*
1515
* IDENTIFICATION
16-
* $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.228 2002/06/1519:54:23 momjian Exp $
16+
* $Header: /cvsroot/pgsql/src/backend/commands/vacuum.c,v 1.229 2002/06/1521:52:31 tgl Exp $
1717
*
1818
*-------------------------------------------------------------------------
1919
*/
@@ -158,9 +158,8 @@ static bool enough_space(VacPage vacpage, Size len);
158158
void
159159
vacuum(VacuumStmt*vacstmt)
160160
{
161-
MemoryContextanl_context,
162-
old_context;
163161
constchar*stmttype=vacstmt->vacuum ?"VACUUM" :"ANALYZE";
162+
MemoryContextanl_context=NULL;
164163
List*vrl,
165164
*cur;
166165

@@ -188,7 +187,8 @@ vacuum(VacuumStmt *vacstmt)
188187
/*
189188
* Send info about dead objects to the statistics collector
190189
*/
191-
pgstat_vacuum_tabstat();
190+
if (vacstmt->vacuum)
191+
pgstat_vacuum_tabstat();
192192

193193
/*
194194
* Create special memory context for cross-transaction storage.
@@ -203,6 +203,10 @@ vacuum(VacuumStmt *vacstmt)
203203
ALLOCSET_DEFAULT_INITSIZE,
204204
ALLOCSET_DEFAULT_MAXSIZE);
205205

206+
/*
207+
* If we are running only ANALYZE, we don't need per-table transactions,
208+
* but we still need a memory context with table lifetime.
209+
*/
206210
if (vacstmt->analyze&& !vacstmt->vacuum)
207211
anl_context=AllocSetContextCreate(QueryContext,
208212
"Analyze",
@@ -214,28 +218,40 @@ vacuum(VacuumStmt *vacstmt)
214218
vrl=getrels(vacstmt->relation,stmttype);
215219

216220
/*
217-
*Formerly, there was code here to prevent more than one VACUUM from
218-
*executing concurrently in the same database. However, there's no
219-
*good reason to prevent that, and manually removing lockfiles after
220-
*a vacuum crash was a pain for dbadmins. So, forget about lockfiles,
221-
*and just rely on the locks we grab on each target table
222-
*to ensure that there aren't two VACUUMs running on the same table
223-
*at the same time.
221+
* Formerly, there was code here to prevent more than one VACUUM from
222+
* executing concurrently in the same database. However, there's no
223+
* good reason to prevent that, and manually removing lockfiles after
224+
* a vacuum crash was a pain for dbadmins. So, forget about lockfiles,
225+
* and just rely on the locks we grab on each target table
226+
* to ensure that there aren't two VACUUMs running on the same table
227+
* at the same time.
228+
*/
229+
230+
/*
231+
* The strangeness with committing and starting transactions here is due
232+
* to wanting to run each table's VACUUM as a separate transaction, so
233+
* that we don't hold locks unnecessarily long. Also, if we are doing
234+
* VACUUM ANALYZE, the ANALYZE part runs as a separate transaction from
235+
* the VACUUM to further reduce locking.
236+
*
237+
* vacuum_rel expects to be entered with no transaction active; it will
238+
* start and commit its own transaction. But we are called by an SQL
239+
* command, and so we are executing inside a transaction already. We
240+
* commit the transaction started in PostgresMain() here, and start
241+
* another one before exiting to match the commit waiting for us back in
242+
* PostgresMain().
224243
*
225-
*The strangeness with committing and starting transactions in the
226-
*init and shutdown routines is due to the fact that the vacuum cleaner
227-
*is invoked via an SQL command, and so is already executing inside
228-
*a transaction.We need to leave ourselves in a predictable state
229-
*on entry and exit to the vacuum cleaner. We commit the transaction
230-
*started in PostgresMain() inside vacuum_init(), and start one in
231-
*vacuum_shutdown() to match the commit waiting for us back in
232-
*PostgresMain().
244+
* In the case of an ANALYZE statement (no vacuum, just analyze) it's
245+
* okay to run the whole thing in the outer transaction, and so we skip
246+
* transaction start/stop operations.
233247
*/
234248
if (vacstmt->vacuum)
235249
{
236250
if (vacstmt->relation==NULL)
237251
{
238252
/*
253+
* It's a database-wide VACUUM.
254+
*
239255
* Compute the initially applicable OldestXmin and FreezeLimit
240256
* XIDs, so that we can record these values at the end of the
241257
* VACUUM. Note that individual tables may well be processed with
@@ -261,11 +277,7 @@ vacuum(VacuumStmt *vacstmt)
261277
}
262278

263279
/*
264-
* Process each selected relation.We are careful to process each
265-
* relation in a separate transaction in order to avoid holding too
266-
* many locks at one time.Also, if we are doing VACUUM ANALYZE, the
267-
* ANALYZE part runs as a separate transaction from the VACUUM to
268-
* further reduce locking.
280+
* Loop to process each selected relation.
269281
*/
270282
foreach(cur,vrl)
271283
{
@@ -275,7 +287,14 @@ vacuum(VacuumStmt *vacstmt)
275287
vacuum_rel(relid,vacstmt,RELKIND_RELATION);
276288
if (vacstmt->analyze)
277289
{
278-
/* If we vacuumed, use new transaction for analyze. */
290+
MemoryContextold_context=NULL;
291+
292+
/*
293+
* If we vacuumed, use new transaction for analyze. Otherwise,
294+
* we can use the outer transaction, but we still need to call
295+
* analyze_rel in a memory context that will be cleaned up on
296+
* return (else we leak memory while processing multiple tables).
297+
*/
279298
if (vacstmt->vacuum)
280299
StartTransactionCommand();
281300
else
@@ -287,16 +306,18 @@ vacuum(VacuumStmt *vacstmt)
287306
CommitTransactionCommand();
288307
else
289308
{
290-
MemoryContextResetAndDeleteChildren(anl_context);
291309
MemoryContextSwitchTo(old_context);
310+
MemoryContextResetAndDeleteChildren(anl_context);
292311
}
293312
}
294313
}
295314

296-
/* clean up */
315+
/*
316+
* Finish up processing.
317+
*/
297318
if (vacstmt->vacuum)
298319
{
299-
/*on entry, we are not in a transaction */
320+
/*here, we are not in a transaction */
300321

301322
/* matches the CommitTransaction in PostgresMain() */
302323
StartTransactionCommand();
@@ -322,9 +343,8 @@ vacuum(VacuumStmt *vacstmt)
322343
MemoryContextDelete(vac_context);
323344
vac_context=NULL;
324345

325-
if (vacstmt->analyze&& !vacstmt->vacuum)
346+
if (anl_context)
326347
MemoryContextDelete(anl_context);
327-
328348
}
329349

330350
/*

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