From: | Vadim Mikheev <vadim(at)krs(dot)ru> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: [HACKERS] Notice: heap_open/close changes committed |
Date: | 1999-09-20 01:24:31 |
Message-ID: | 37E58CCF.32C57B87@krs.ru |
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Lists: | pgsql-hackers |
Tom Lane wrote:
>
> 2. I made most opens of system relations grab AccessShareLock if
> read-only, or RowExclusiveLock if read-write, on the theory that
^^^^^^^^^^^^^^^^
> these accesses correspond to an ordinary search or update of a user
> relation. This maximizes concurrency of access to the system tables.
There are problems here. In the case of normal UPDATE/DELETE
(when RowExclusiveLock is acquired) Executor takes care about
the-same-row writers, but other parts of system don't check
is tuple read being updated concurrent transaction or not.
This is the old bug (pre-6.5.X released WRITE lock just after
system table was modified). I had no time to fix it and so
just changed old WRITE lock with new AccessExclusiveLock.
But we have to handle this in proper way (wait if t_xmax
is id of an active transaction).
Vadim
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