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Re: increasing the default WAL segment size

Stephen Frost <sfrost@snowman.net>

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From: Stephen Frost <sfrost@snowman.net>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
Cc: David Steele <david@pgmasters.net>, Robert Haas <robertmhaas@gmail.com>, Beena Emerson <memissemerson@gmail.com>, tushar <tushar.ahuja@enterprisedb.com>, Prabhat Sahu <prabhat.sahu@enterprisedb.com>, Ashutosh Sharma <ashu.coek88@gmail.com>, Jim Nasby <Jim.Nasby@bluetreble.com>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Andres Freund <andres@anarazel.de>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-03-25T16:59:22Z
Lists: pgsql-hackers 
Peter,

* Peter Eisentraut (peter.eisentraut@2ndquadrant.com) wrote:
> On 3/24/17 08:18, Stephen Frost wrote:
> > Beyond that, this also bakes in an assumption that we would then require
> > access to a database
> 
> That is a good point, but then any change to the naming whatsoever will
> create trouble.  Then we might as well choose which specific trouble.

Right, and I'd rather we work that out before we start encouraging users
to change their WAL segment size, which is what this patch will do.

Personally, I'm alright with the patch David has produced, which is
pretty small, maintains the same names when 16MB segments are used, and
is pretty straight-forward to reason about.  I do think it'll need added
documentation to clarify how WAL segment names are calculated and
perhaps another function which returns the size of WAL segments on a
given cluster (I don't think we have that..?), and, ideally, added
regression tests or buildfarm animals which try different sizes.

On the other hand, I don't have any particular issue with the naming
scheme you proposed up-thread, which uses proper separators between the
components of a WAL filename, but that would change what happens with
16MB WAL segments today.

I'm still of the opinion that we should be changing the default to 64MB
for WAL segments.

Thanks!

Stephen

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Make WAL segment size configurable at initdb time.

  2. Perform only one ReadControlFile() during startup.

  3. Introduce BYTES unit for GUCs.

  4. Remove useless duplicate inclusions of system header files.

  5. Refactor other replication commands to use DestRemoteSimple.

  6. Add a SHOW command to the replication command language.

  7. Add a new DestReceiver for printing tuples without catalog access.

  8. Support fls().

  9. Extend yesterday's patch making BLCKSZ and RELSEG_SIZE configurable to also

  10. Commit the reasonably uncontroversial parts of J.R. Nield's PITR patch, to

  11. XLOG (also known as WAL -:)) Bootstrap/Startup/Shutdown.

  12. Transaction log manager core code.