Horton

Re: Re: Cache relation sizes?

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: 陈佳昕(步真) <buzhen.cjx@alibaba-inc.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Konstantin Knizhnik <k.knizhnik@postgrespro.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-12-23T23:03:52Z
Lists: pgsql-hackers 
On Wed, Dec 23, 2020 at 1:31 AM 陈佳昕(步真) <buzhen.cjx@alibaba-inc.com> wrote:
> I studied your patch these days and found there might be a problem.
> When execute 'drop database', the smgr shared pool will not be removed because of no call 'smgr_drop_sr'. Function 'dropdb' in dbcommands.c remove the buffer from bufferpool and unlink the real files by 'rmtree', It doesn't call smgrdounlinkall, so the smgr shared cache will not be dropped although the table has been removed. This will cause some errors when smgr_alloc_str -> smgropen、smgrimmedsync. Table file has been removed, so smgropen and smgrimmedsync will get a unexpected result.

Hi Buzhen,

Thanks, you're right -- it needs to scan the pool of SRs and forget
everything from the database you're dropping.

Commits

  1. Optimize DropRelFileNodesAllBuffers() for recovery.

  2. Cache smgrnblocks() results in recovery.

  3. Use pg_pread() and pg_pwrite() for data files and WAL.

  4. Add a check to prevent overwriting valid data if smgrnblocks() gives a