| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com> |
| Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Jerry Jelinek <jerry(dot)jelinek(at)joyent(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: patch to allow disable of WAL recycling |
| Date: | 2019-03-06 16:47:02 |
| Message-ID: | CA+TgmoZgXLa4iBKnRzxPbO0Zqc3qcRWHMpiY1t6K51rvQzyZfQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Mar 6, 2019 at 11:37 AM Andrew Dunstan
<andrew(dot)dunstan(at)2ndquadrant(dot)com> wrote:
> Well, let's put the question another way. Is there any reason to allow
> skipping zero filling if we are recycling? That seems possibly
> dangerous. I can imagine turning off recycling but leaving on
> zero-filling, although I don't have a concrete use case for it ATM.
I think the short answer is that we don't know. Any filesystem where
just writing the last byte of the file is good enough to guarantee
that all the intervening space is allocated can skip zero-filling.
Any system where creating new WAL files is faster than recycling old
ones can choose to do it that way. I don't know how you can make a
categorical argument that there can't be a system where one of those
things -- either one -- is true and the other is false. At least to
me, they seem like basically unrelated issues.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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