Re: Performance Question

От: Fernando Hevia
Тема: Re: Performance Question
Дата: ,
Msg-id: 14FCA72EC23448AB8207FC08D52094F4@iptel.com.ar
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Ответ на: Performance Question  (- -)
Список: pgsql-performance

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Performance Question  (- -, )
 Re: Performance Question  ("J Sisson", )
 Re: Performance Question  (, )
 Re: Performance Question  ("Fernando Hevia", )
 Re: Performance Question  (Tom Lane, )
  Re: Performance Question  ("Dave Page", )
 Re: Performance Question  ("Scott Marlowe", )
 Re: Performance Question  ("Merlin Moncure", )
 Re: Performance Question  (PFC, )

Incrementing shared_buffers to 1024MB and set effective_cache_size to 6000MB and test again.
To speed up sort operations, increase work_mem till you notice an improvement.
Play with those settings with different values.
 


De: [mailto:] En nombre de - -
Enviado el: Miércoles, 12 de Noviembre de 2008 14:28
Para:
Asunto: [PERFORM] Performance Question

I've been searching for performance metrics and tweaks for a few weeks now. I'm trying to determine if the length of time to process my queries is accurate or not and I'm having a difficult time determining that. I know postgres performance is very dependent on hardware and settings and I understand how difficult it is to tackle. However, I was wondering if I could get some feedback based on my results please.

The database is running on a dual-core 2GHz Opteron processor with 8GB of RAM. The drives are 10K RPM 146GB drives in RAID 5 (I've read RAID 5 is bad for Postgres, but moving the database to another server didn't change performance at all). Some of the key parameters from postgresql.conf are:

max_connections = 100
shared_buffers = 16MB
work_mem = 64MB
everything else is set to the default

One of my tables has 660,000 records and doing a SELECT * from that table (without any joins or sorts) takes 72 seconds. Ordering the table based on 3 columns almost doubles that time to an average of 123 seconds. To me, those numbers are crazy slow and I don't understand why the queries are taking so long. The tables are UTF-8 encode and contain a mix of languages (English, Spanish, etc). I'm running the query from pgadmin3 on a remote host. The server has nothing else running on it except the database.

As a test I tried splitting up the data across a number of other tables. I ran 10 queries (to correspond with the 10 tables) with a UNION ALL to join the results together. This was even slower, taking an average of 103 seconds to complete the generic select all query.

I'm convinced something is wrong, I just can't pinpoint where it is. I can provide any other information necessary. If anyone has any suggestions it would be greatly appreciated.


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