| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com> |
| Cc: | "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Changing default value of wal_sync_method to open_datasync on Linux |
| Date: | 2018-02-20 00:33:13 |
| Message-ID: | 20180220003313.kfytfs3cqsz7li4l@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2018-02-20 00:27:47 +0000, Tsunakawa, Takayuki wrote:
> I propose changing the default value of wal_sync_method from fdatasync
> to open_datasync on Linux. The patch is attached. I'm feeling this
> may be controversial, so I'd like to hear your opinions.
Indeed. My past experience with open_datasync on linux shows it to be
slower by roughly an order of magnitude. Even if that would turn out not
to be the case anymore, I'm *extremely* hesitant to make such a change.
> [HDD on VM, ext4 volume mounted with noatime,nobarrier,data=writeback]
> (the figures seem oddly high, though; this may be due to some VM
> configuration)
These numbers clearly aren't reliable, there's absolutely no way an hdd
can properly do ~30k syncs/sec. Until there's reliable numbers this
seems moot.
Greetings,
Andres Freund
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