| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Heikki Linnakangas <hlinnaka(at)iki(dot)fi>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
| Subject: | Re: [Proposal] Fully WAL logged CREATE DATABASE - No Checkpoints |
| Date: | 2022-08-05 00:21:26 |
| Message-ID: | 3696676.1659658886@sss.pgh.pa.us |
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Andres Freund <andres(at)anarazel(dot)de> writes:
> On August 4, 2022 4:11:13 PM PDT, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> [pile^2] Also, what is the rationale for locking the target buffer
>> but not the source buffer? That seems pretty hard to justify from
>> here, even granting the assumption that we don't expect any other
>> processes to be interested in these buffers (which I don't grant,
>> because checkpointer).
> I'm not arguing it's good or should stay that way, but it's probably okayish that checkpointer / bgwriter have access, given that they will never modify buffers. They just take a lock to prevent concurrent modifications, which RelationCopyStorageUsingBuffer hopefully doesn't do.
I'm not arguing that it's actively broken today --- but AFAIR,
every other access to a shared buffer takes a buffer lock.
It does not seem to me to be very future-proof for this code to
decide it's exempt from that rule, without so much as a comment
justifying it. Furthermore, what's the gain? We aren't expecting
contention here, I think. If we were, then it probably *would* be
actively broken.
regards, tom lane
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