Re: Update big table

Thanks.

I have fixed the problem. And now the query can run in 4 mins for 1.5 million records in TABLE1 and 0.5 million records in TABLE2.

The solution is I created a function that gets all event_id from TABLE2 then travel through each event_id and do the update for TABLE1. This removes the side effects of using IN predicate. Also I have
1. set FILLFACTOR = 70
2. remove trigger and index before the function, create index based on event_id
3. add trigger and index back after run function.

Regards,
Haiming

From: BladeOfLight16 [mailto:bladeoflight16(at)gmail(dot)com]
Sent: Monday, 15 July 2013 5:26 AM
To: pgsql-general(at)postgresql(dot)org; Haiming Zhang
Subject: Re: [GENERAL] Update big table

I don't believe you can use JOIN explicitly in this situation because it's an UPDATE, but I believe you can accomplish the same effect with FROM and WHERE.

UPDATE table SET column1 = TRUE
FROM table2
WHERE table1.event_id = table2.event_id;

I would make sure there's an index on table2.event_id if it's not the PK. If it's part of a composite key, either make sure that table2.event_id is the first column in the index (PostgreSQL will use an index like that; right?) or create an index where it is.

(Sorry. Forgot to hit Reply All.)
On Sun, Jul 14, 2013 at 7:03 AM, Vincenzo Romano <vincenzo(dot)romano(at)notorand(dot)it<mailto:vincenzo(dot)romano(at)notorand(dot)it>> wrote:
2013/7/14 Haiming Zhang <Haiming(dot)Zhang(at)redflex(dot)com(dot)au<mailto:Haiming(dot)Zhang(at)redflex(dot)com(dot)au>>:
> Hi All,
>
>
>
> I am using postgres 9.1, I have a question about updating big table. Here is
> the basic information of this table.
>
> 1. This table has one primary key and other 11 columns.
>
> 2. It also has a trigger that before update records,
> another table got updated first.
>
> 3. The has millions of records now.
> 4. I am not allowed to delete records in this table when
> UPDATE
>
> The problem is when I do a "Update" query it takes a long time to execute.
> Eg. when I run query like this " update TABLE set column1 = true where
> EVENT_ID in (select EVENT_ID from TABLE2 );" , it took hours to update the
> whole table. In order to optimize the update speed. I tried the following
> strategies:
>
> 1. create index based on primary key, column1 and
> combination of primary key and column1.
>
> 2. Alter FILLFACTOR = 70, vacuum all and then reindex
>
> 3. drop trigger before update
>
> Then I use "EXPLAIN" to estimate query plan, all of the above strategies do
> not improve the UPDATE speed dramatically.
>
>
>
> Please comments on my three strategies (eg, does I index too many columns in
> 1?) and please advise me how to improve the update speed. Any advice is
> welcomed. I appreciate all you help.
>
>
>
> Thanks,
>
>
>
> Regards,
>
> Haiming
A JOIN would solve your speed problem.
The IN() predicate is the cause.
AFAIK.

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