From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | gunni(at)if(dot)is |
Cc: | pgsql-general(at)postgreSQL(dot)org, pgsql-sql(at)postgreSQL(dot)org |
Subject: | Re: [SQL] Bad update performance? |
Date: | 1999-07-21 13:38:13 |
Message-ID: | 1666.932564293@sss.pgh.pa.us |
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Lists: | pgsql-general pgsql-sql |
"Gunnar Ingvi Thorisson" <gunni(at)if(dot)is> writes:
> Ive a table with about 142000 rows like shown below and I want to
> set field "divis" to "unknown" by executing following update command:
> update ipacct set divis = 'unknown';
> However this seems to take hours,
Well, updating 142000 rows is going to take a little while...
Are you starting the postmaster with -o -F ? That makes for a pretty
considerable speedup in most cases (at the cost of trouble if you
have a system crash during an update).
> Does indexing the field "divis" speed up the update performance?
No, it would not help a query like that --- though if you added a clause
like "where divis = 'oldvalue'" then an index would help to find the
rows that need updated. Actually, every index you add *slows down*
updates, since all the indexes must be updated along with the table.
regards, tom lane
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