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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 the
expected state.  In the original coding, we'd fail to advance
next_to_clean, causing that buffer to be probably-uselessly rechecked next
time, and also have an off-by-one idea of the number of buffers scanned.
This commit is contained in:
Tom Lane 2007-09-25 22:11:48 +00:00
parent 6f5c38dcd0
commit 7a315a09dc
1 changed files with 11 additions and 10 deletions
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21
src/backend/storage/buffer/bufmgr.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.225 2007/09/25 20:03:37 tgl Exp $
* $PostgreSQL: pgsql/src/backend/storage/buffer/bufmgr.c,v 1.226 2007/09/25 22:11:48 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -1324,10 +1324,17 @@ BgBufferSync(void)
reusable_buffers = reusable_buffers_est;
/* Execute the LRU scan */
while (num_to_scan-- > 0 && reusable_buffers < upcoming_alloc_est)
while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est)
{
int buffer_state = SyncOneBuffer(next_to_clean, true);
if (++next_to_clean >= NBuffers)
{
next_to_clean = 0;
next_passes++;
}
num_to_scan--;
if (buffer_state & BUF_WRITTEN)
{
reusable_buffers++;
@ -1339,12 +1346,6 @@ BgBufferSync(void)
}
else if (buffer_state & BUF_REUSABLE)
reusable_buffers++;
if (++next_to_clean >= NBuffers)
{
next_to_clean = 0;
next_passes++;
}
}
BgWriterStats.m_buf_written_clean += num_written;
@ -1353,7 +1354,7 @@ BgBufferSync(void)
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",
recent_alloc, smoothed_alloc, strategy_delta, bufs_ahead,
smoothed_density, reusable_buffers_est, upcoming_alloc_est,
bufs_to_lap - num_to_scan - 1,
bufs_to_lap - num_to_scan,
num_written,
reusable_buffers - reusable_buffers_est);
#endif
@ -1366,7 +1367,7 @@ BgBufferSync(void)
* scanning, which is helpful because a long memory isn't as desirable
* on the density estimates.
*/
strategy_delta = bufs_to_lap - num_to_scan - 1;
strategy_delta = bufs_to_lap - num_to_scan;
recent_alloc = reusable_buffers - reusable_buffers_est;
if (strategy_delta > 0 && recent_alloc > 0)
{