| From: | "A(dot) Kretschmer" <andreas(dot)kretschmer(at)schollglas(dot)com> |
|---|---|
| To: | pgsql-general(at)postgresql(dot)org |
| Subject: | Re: About updates |
| Date: | 2006-03-10 16:08:48 |
| Message-ID: | 20060310160848.GA21806@webserv.wug-glas.de |
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| Lists: | pgsql-general |
am 10.03.2006, um 10:46:39 -0500 mailte Emi Lu folgendes:
> Hello,
>
> postgresql 8.0.1, in a plpgsql function
>
> To update columns' values in a table (without OID), if I ran:
> 1. "update table1 set col1 = ..., col2 = ... ... col100 ="
>
> or
> 2.
> "update table1 set col1 = "
> ...
> "update table1 set col100 = "
>
> way 1 only has one disk I/O, right? While way 2 is more time consuming
> since there is disk I/O when a update is ran.
Because of MVCC every UPDATE is practical a DELETE + INSERT.
Way1: you have only one DELETE+INSERT, Way2 one hundred, and you have
100 dead rows until the next VACUUM.
HTH, Andreas
--
Andreas Kretschmer (Kontakt: siehe Header)
Heynitz: 035242/47215, D1: 0160/7141639
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