Re: Why BgWriterDelay is fixed? - Mailing list pgsql-general

You can check the code in guc.c,  search "bgwriter_delay",  &BgWriterDelay<br />In the global user configuration,
itcan change the value of BgWriterDelay.<br />Since the BgWriterDelay declared in bgwriter.h as extern.  It can be
changedin the global namespace.<br /><br /><div><div style="color:#909090;font-family:Arial
Narrow;font-size:12px">------------------</div><divstyle="font-size:14px;font-family:Verdana;color:#000;"><div><div
style="font-family:'lucida Grande', Verdana; font-size: 12px; line-height: 18px; ">Thanks&Regards,</div><div
style="font-family:'lucida Grande', Verdana; font-size: 12px; line-height: 18px; ">Xiong He<br /><br
/></div></div></div></div><div> </div><div><div><br/></div><div><br /></div><div style="font-size: 12px;font-family:
ArialNarrow;padding:2px 0 2px 0;">------------------ Original ------------------</div><div style="font-size:
12px;background:#efefef;padding:8px;"><div><b>From:</b> "高健"<luckyjackgao@gmail.com>;</div><div><b>Date:
</b> Mon,Oct 29, 2012 03:17 PM</div><div><b>To: </b> "pgsql-general"<pgsql-general@postgresql.org>; <wbr
/></div><div></div><div><b>Subject:</b> [GENERAL] Why BgWriterDelay is fixed?</div></div><div><br
/></div>In src/backend/postmaster/bgwriter.c, I can find the following source code(PostgreSQL9.2):<div><br
/></div><div><div><br/></div><div>/*</div><div> * GUC parameters</div><div> */</div><div>int<span
class="Apple-tab-span"style="white-space:pre"> </span>BgWriterDelay = 200;</div></div><div><br
/></div><div>...</div><div><div><spanclass="Apple-tab-span" style="white-space:pre"> </span>rc =
WaitLatch(&MyProc->procLatch,</div><div><spanclass="Apple-tab-span" style="white-space:pre"> </span>  
WL_LATCH_SET| WL_TIMEOUT | WL_POSTMASTER_DEATH,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>
 BgWriterDelay /* ms */ );</div></div><div>...</div><div><div><span class="Apple-tab-span" style="white-space:pre">
</span>if(rc == WL_TIMEOUT && can_hibernate && prev_hibernate)</div><div><span class="Apple-tab-span"
style="white-space:pre"></span>{</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>/* Ask for
notificationat next buffer allocation */</div><div><span class="Apple-tab-span" style="white-space:pre">
</span>StrategyNotifyBgWriter(&MyProc->procLatch);</div><div><spanclass="Apple-tab-span"
style="white-space:pre"></span>/* Sleep ... */</div><div><span class="Apple-tab-span" style="white-space:pre">
</span>rc= WaitLatch(&MyProc->procLatch,</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>
 WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,</div><div><span class="Apple-tab-span" style="white-space:pre">
</span>  BgWriterDelay * HIBERNATE_FACTOR);</div><div><span class="Apple-tab-span" style="white-space:pre"> </span>/*
Resetthe notification request in case we timed out */</div><div><span class="Apple-tab-span" style="white-space:pre">
</span>StrategyNotifyBgWriter(NULL);</div><div><spanclass="Apple-tab-span" style="white-space:pre">
</span>}</div></div><div><br/></div><div>But I also found  the following in
postgresql.conf:</div><div><div>#bgwriter_delay= 200ms                 # 10-10000ms between rounds</div></div><div>It
isnow comment .</div><div>But according to the fixed code of  BgWriterDelay = 200, even when I update bgwriter_delay in
postgresql.confto a different value(eg 300ms), </div><div>how can it ovewrite the fixed  200ms in bgwriter.c
?</div><div><br/></div><div>I also want to know,  if it is not a bug, then what is the reason?</div></div>