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Re: gprof SELECT COUNT(*) results

From: "Zeugswetter Andreas DCP SD" <ZeugswetterA(at)spardat(dot)at>
To: <simon(at)2ndquadrant(dot)com>,<tgl(at)sss(dot)pgh(dot)pa(dot)us>,<chriskl(at)familyhealth(dot)com(dot)au>,<pgsql-hackers(at)postgresql(dot)org>,<zhouqq(at)cs(dot)toronto(dot)edu>
Subject: Re: gprof SELECT COUNT(*) results
Date: 2005-11-29 14:27:59
Message-ID: E1539E0ED7043848906A8FF995BDA579A16527@m0143.s-mxs.net (view raw or flat)
Thread:
Lists: pgsql-hackers
> DB2:
> Uncommitted Read (UR) mode "Dirty read" isn't the default, or 
> the recommended lock level for most apps. I was considering 
> Cursor Stability mode (or higher), which is the default 

Sorry, they call it "read committed" but actually do cursor stability,
which does keep one lock on the last fetched row. Keeping the lock would

actually not be necessary to conform with ANSI "read committed".

See table 4 on Page 8 of
http://www.cs.ndsu.nodak.edu/~yawang/Snapshot.ppt

> SQLServer:
> READ COMMITTED does take share locks.

But it does not hold them. According to docu it holds them "while
reading" which 
is not a very detailed description. How long is that really, e.g. with
odbc forward 
cursor fetch ?

> There's a NO LOCK hint, true, but its not a default.

That is for dirty/uncommitted reads.

Andreas

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