ソースコードからPostgreSQLのbgwriter_を理解するlru_maxpages
7798 ワード
コード:srcbackendstoragebufferbufmgr.c
上記のコードから、
開宗明義、人はすでに注釈の中で言った:This is is called periodically by the background writer process.
bgwriter_についてはlru_maxpages:
/* * If we're not running the LRU scan, just stop after doing the stats * stuff. We mark the saved state invalid so that we can recover sanely * if LRU scan is turned back on later. */if (bgwriter_lru_maxpages <= 0) { saved_info_valid = false; return true; }
bgwriter_lru_maxpages<=0であれば、すぐに戻ります.汚いデータの読み書きはまったく行わない.
もう一度見てください.
while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est) { …… if (buffer_state & BUF_WRITTEN) { reusable_buffers++; if (++num_written >= bgwriter_lru_maxpages) { BgWriterStats.m_maxwritten_clean++; break; } } …… }
bgwriterを超えるとlru_maxpagesも、再書き込みを停止します.
/*
* BgBufferSync -- Write out some dirty buffers in the pool.
*
* This is called periodically by the background writer process.
*
* Returns true if it's appropriate for the bgwriter process to go into
* low-power hibernation mode. (This happens if the strategy clock sweep
* has been "lapped" and no buffer allocations have occurred recently,
* or if the bgwriter has been effectively disabled by setting
* bgwriter_lru_maxpages to 0.)
*/
bool
BgBufferSync(void)
{
……
/*
* If we're not running the LRU scan, just stop after doing the stats
* stuff. We mark the saved state invalid so that we can recover sanely
* if LRU scan is turned back on later.
*/
if (bgwriter_lru_maxpages <= 0)
{
saved_info_valid = false;
return true;
}
……
/*
* Now write out dirty reusable buffers, working forward from the
* next_to_clean point, until we have lapped the strategy scan, or cleaned
* enough buffers to match our estimate of the next cycle's allocation
* requirements, or hit the bgwriter_lru_maxpages limit.
*/
/* Make sure we can handle the pin inside SyncOneBuffer */
ResourceOwnerEnlargeBuffers(CurrentResourceOwner);
num_to_scan = bufs_to_lap;
num_written = 0;
reusable_buffers = reusable_buffers_est;
/* Execute the LRU scan */
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++;
if (++num_written >= bgwriter_lru_maxpages)
{
BgWriterStats.m_maxwritten_clean++;
break;
}
}
else if (buffer_state & BUF_REUSABLE)
reusable_buffers++;
}
BgWriterStats.m_buf_written_clean += num_written;
……
/* Return true if OK to hibernate */
return (bufs_to_lap == 0 && recent_alloc == 0);
} 上記のコードから、
開宗明義、人はすでに注釈の中で言った:This is is called periodically by the background writer process.
bgwriter_についてはlru_maxpages:
/* * If we're not running the LRU scan, just stop after doing the stats * stuff. We mark the saved state invalid so that we can recover sanely * if LRU scan is turned back on later. */if (bgwriter_lru_maxpages <= 0) { saved_info_valid = false; return true; }
bgwriter_lru_maxpages<=0であれば、すぐに戻ります.汚いデータの読み書きはまったく行わない.
もう一度見てください.
while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est) { …… if (buffer_state & BUF_WRITTEN) { reusable_buffers++; if (++num_written >= bgwriter_lru_maxpages) { BgWriterStats.m_maxwritten_clean++; break; } } …… }
bgwriterを超えるとlru_maxpagesも、再書き込みを停止します.