From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> |
Cc: | drkp(at)csail(dot)mit(dot)edu, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: serializable read only deferrable |
Date: | 2010-12-08 01:36:13 |
Message-ID: | 2844.1291772173@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> Oh, I just went through the code on setting READ ONLY and discovered
> that contrary to the standard *and* the PostgreSQL documentation,
> you can change the status of a transaction between READ ONLY and
> READ WRITE at will. Yeah, that's a problem for my intended use.
> Many optimizations would need to go right out the window, and the
> false positive rate under SSI would be high.
I believe you had better support the locution
begin;
set transaction read only;
...
I agree that letting it be changed back to read/write after that is
surprising and unnecessary. Perhaps locking down the setting at the
time of first grabbing a snapshot would be appropriate. IIRC that's
how it works for transaction isolation level, and this seems like it
ought to work the same.
regards, tom lane
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