Re: strategies for dealing with frequently updated tables

On 2/28/2012 2:09 PM, Dave Vitek wrote:
>>> The following query takes about 100 minutes (3 seconds per tuple):
>>> SELECT count(id) from T
>>
>> so table T has 18,000 rows? (100 * 60 * 3)
> 100 minutes * 60 (sec/min) / 3 (sec/tuple) = 2000 tuples

Well... math was never my strong point :-)

>> So you have a large row, who knows how many, and the problem is
>> "SELECT count(id) from T" is slow?
> Correct. I think anything requiring a sequential scan of the table takes
> 100 minutes to run. However, I wanted to be careful about drawing
> conclusions and just present data.
>>
>>
>> -Andy
>> ps: based on you're email gramma, I almost changed all your to you're,
>> just to see if it annoyed you. Sounds like you work for grammar
>> technology.
> How embarrassing! After writing code all day I tend to have some natural
> language issues.

No, no, that's not what I meant. Your email address grammatech.com,
makes it sound like you are doing grammar technology.

Have you checked for table bloat? I thought I saw a sql statement
someplace that did that.

I'm not sure what it actually means, but this row would make me worry:

INFO: "T": found 0 removable, 1444 nonremovable row versions in 1522
out of 299964 pages
DETAIL: 30 dead row versions cannot be removed yet.

Hopefully somebody else is reading along that can offer insight.

Have you always had this problem, or is it something new? Or is "select
count..." new?

Also, not sure if you have seen it elsewhere, but "select count"'ing an
entire table is probably one of PG slowest operations. If you really
need the count you might consider a separate summary table that stores
the count.

-Andy