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vacuum_mem

From: Litao Wu <litaowu(at)yahoo(dot)com>
To: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Cc: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: vacuum_mem
Date: 2004-07-08 18:03:43
Message-ID: 20040708180343.88032.qmail@web13121.mail.yahoo.com (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,

I tested vacuum_mem setting under a 
4CPU and 4G RAM machine. I am the only person 
on that machine.

The table:
         tablename         | size_kb |   reltuples
---------------------------+-------------------------
 big_t                     | 2048392 |   7.51515e+06

Case 1:
1. vacuum full big_t;
2. begin;
   update big_t set email = lpad('a', 255, 'b');
   rollback;
3. set vacuum_mem=655360; -- 640M
4. vacuum big_t;
It takes 1415,375 ms
Also from top, the max SIZE is 615M while 
SHARE is always 566M

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM
  TIME COMMAND
5914 postgres  16   0   615M 615M  566M D     7.5 15.8
 21:21 postgres: postgres mydb xxx.xxx.xxx.xxx:34361
VACUUM

Case 2:
1. vacuum full big_t;
2. begin;
   update big_t set email = lpad('a', 255, 'b');
   rollback;
3. set vacuum_mem=65536; -- 64M
4. vacuum big_t;
It takes 1297,798 ms
Also from top, the max SIZE is 615M while 
SHARE is always 566M

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM
  TIME COMMAND
 3613 postgres  15   0  615M 615M  566M D    17.1 15.8
  9:04 postgres: postgres mydb xxx.xxx.xxx.xxx:34365
VACUUM

It seems vacuum_mem does not have performance 
effect at all.

In reality, we vaccum nightly and I want to find out 
which vacuum_mem value is the 
best to short vacuum time.

Any thoughts?

Thanks,


		
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