| From: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net> |
| Cc: | David Steele <david(at)pgmasters(dot)net>, Beena Emerson <memissemerson(at)gmail(dot)com>, tushar <tushar(dot)ahuja(at)enterprisedb(dot)com>, Prabhat Sahu <prabhat(dot)sahu(at)enterprisedb(dot)com>, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com>, Jim Nasby <Jim(dot)Nasby(at)bluetreble(dot)com>, Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: increasing the default WAL segment size |
| Date: | 2017-03-21 22:59:57 |
| Message-ID: | 35b71b68-5d92-cfee-5fb3-50c77deeeb11@2ndquadrant.com |
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| Lists: | pgsql-hackers |
On 3/21/17 15:22, Robert Haas wrote:
> If you take the approach that Beena did, then you lose the
> correspondence with LSNs, which is admittedly not great but there are
> already helper functions available to deal with LSN -> filename
> mappings and I assume those will continue to work. If you take the
> opposite approach, then WAL filenames stop being consecutive, which
> seems to me to be far worse in terms of user and tool confusion.
Anecdotally, I think having the file numbers consecutive is very
important, for debugging and feel-good factor.
If you want to raise the segment size and preserve the LSN mapping, then
pick 256 MB as your next size.
I do think, however, that this has the potential of creating another
ongoing source of confusion similar to oid vs relfilenode, where the
numbers are often the same, except when they are not. With hindsight, I
would have made the relfilenodes completely different from the OIDs. We
chose to keep them (mostly) the same as the OIDs, for compatibility. We
are seemingly making a similar kind of decision here.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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