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Commit7a315a0

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Dept. of second thoughts: fix loop in BgBufferSync so that the exit when
bgwriter_lru_maxpages is exceeded leaves the loop variables in theexpected state. In the original coding, we'd fail to advancenext_to_clean, causing that buffer to be probably-uselessly rechecked nexttime, and also have an off-by-one idea of the number of buffers scanned.
1 parent6f5c38d commit7a315a0

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+11
-10
lines changed

1 file changed

+11
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‎src/backend/storage/buffer/bufmgr.c

Lines changed: 11 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.225 2007/09/2520:03:37 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.226 2007/09/2522:11:48 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -1324,10 +1324,17 @@ BgBufferSync(void)
13241324
reusable_buffers=reusable_buffers_est;
13251325

13261326
/* Execute the LRU scan */
1327-
while (num_to_scan-->0&&reusable_buffers<upcoming_alloc_est)
1327+
while (num_to_scan>0&&reusable_buffers<upcoming_alloc_est)
13281328
{
13291329
intbuffer_state=SyncOneBuffer(next_to_clean, true);
13301330

1331+
if (++next_to_clean >=NBuffers)
1332+
{
1333+
next_to_clean=0;
1334+
next_passes++;
1335+
}
1336+
num_to_scan--;
1337+
13311338
if (buffer_state&BUF_WRITTEN)
13321339
{
13331340
reusable_buffers++;
@@ -1339,12 +1346,6 @@ BgBufferSync(void)
13391346
}
13401347
elseif (buffer_state&BUF_REUSABLE)
13411348
reusable_buffers++;
1342-
1343-
if (++next_to_clean >=NBuffers)
1344-
{
1345-
next_to_clean=0;
1346-
next_passes++;
1347-
}
13481349
}
13491350

13501351
BgWriterStats.m_buf_written_clean+=num_written;
@@ -1353,7 +1354,7 @@ BgBufferSync(void)
13531354
elog(DEBUG1,"bgwriter: recent_alloc=%u smoothed=%.2f delta=%ld ahead=%d density=%.2f reusable_est=%d upcoming_est=%d scanned=%d wrote=%d reusable=%d",
13541355
recent_alloc,smoothed_alloc,strategy_delta,bufs_ahead,
13551356
smoothed_density,reusable_buffers_est,upcoming_alloc_est,
1356-
bufs_to_lap-num_to_scan-1,
1357+
bufs_to_lap-num_to_scan,
13571358
num_written,
13581359
reusable_buffers-reusable_buffers_est);
13591360
#endif
@@ -1366,7 +1367,7 @@ BgBufferSync(void)
13661367
* scanning, which is helpful because a long memory isn't as desirable
13671368
* on the density estimates.
13681369
*/
1369-
strategy_delta=bufs_to_lap-num_to_scan-1;
1370+
strategy_delta=bufs_to_lap-num_to_scan;
13701371
recent_alloc=reusable_buffers-reusable_buffers_est;
13711372
if (strategy_delta>0&&recent_alloc>0)
13721373
{

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