| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)anarazel(dot)de>, 周正中(德歌) <dege(dot)zzz(at)alibaba-inc(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, 张广舟(明虚) <guangzhou(dot)zgz(at)alibaba-inc(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, 范孝剑(康贤) <funnyxj(dot)fxj(at)alibaba-inc(dot)com>, 曾文旌(义从) <wenjing(dot)zwj(at)alibaba-inc(dot)com>, 窦贤明(执白) <xianming(dot)dxm(at)alibaba-inc(dot)com>, 萧少聪(铁庵) <shaocong(dot)xsc(at)alibaba-inc(dot)com>, 陈新坚(惧留孙) <xinjian(dot)chen(at)alibaba-inc(dot)com> |
| Subject: | Re: Re: [HACKERS] 答复：[HACKERS] 答复：[HACKERS] about fsync in CLOG buffer write |
| Date: | 2015-09-09 14:35:21 |
| Message-ID: | 30527.1441809321@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> ... How often such a workload actually has to replace a *dirty* clog
> buffer obviously depends on how often you checkpoint, but if you're
> getting ~28k TPS you can completely fill 32 clog buffers (1 million
> transactions) in less than 40 seconds, and you're probably not
> checkpointing nearly that often.
But by the same token, at that kind of transaction rate, no clog page is
actively getting dirtied for more than a couple of seconds. So while it
might get swapped in and out of the SLRU arena pretty often after that,
this scenario seems unconvincing as a source of repeated fsyncs.
Like Andres, I'd want to see a more realistic problem case before
expending a lot of work here.
regards, tom lane
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