Re: Why BgWriterDelay is fixed?

["Xiong He" <iihero@xxxxxx>]

You can check the code in guc.c,  search "bgwriter_delay",  &BgWriterDelay
In the global user configuration, it can change the value of BgWriterDelay.
Since the BgWriterDelay declared in bgwriter.h as extern.  It can be changed in the global namespace.

------------------

Thanks&Regards,

Xiong He

 

------------------ Original ------------------

From:  "高健"<luckyjackgao@xxxxxxxxx>;

Date:  Mon, Oct 29, 2012 03:17 PM

To:  "pgsql-general"<pgsql-general@xxxxxxxxxxxxxx>;

Subject:  [GENERAL] Why BgWriterDelay is fixed?

In src/backend/postmaster/bgwriter.c , I can find the following source code(PostgreSQL9.2):

/*

 * GUC parameters

 */

int BgWriterDelay = 200;

...

rc = WaitLatch(&MyProc->procLatch,

  WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,

  BgWriterDelay /* ms */ );

...

if (rc == WL_TIMEOUT && can_hibernate && prev_hibernate)

{

/* Ask for notification at next buffer allocation */

StrategyNotifyBgWriter(&MyProc->procLatch);

/* Sleep ... */

rc = WaitLatch(&MyProc->procLatch,

  WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,

  BgWriterDelay * HIBERNATE_FACTOR);

/* Reset the notification request in case we timed out */

StrategyNotifyBgWriter(NULL);

}

But I also found  the following in postgresql.conf:

#bgwriter_delay = 200ms                 # 10-10000ms between rounds

It is now comment .

But according to the fixed code of  BgWriterDelay = 200, even when I update bgwriter_delay in postgresql.conf to a different value(eg 300ms), 

how can it ovewrite the fixed  200ms in bgwriter.c ?

I also want to know,  if it is not a bug, then what is the reason?