Shachindra Agarwal wrote:

Dear Postgres Masters:

We are using postgres 7.4 in our java application on RedHat linux. The Java application connects to Postgres via JDBC. The application goes through a ‘discovery’ phase, whereas it adds large amount of data into postgres. Typically, we are adding about a million records in various tables. The application also issues multiple queries to the database at the same time. We do not delete any records during the discovery phase. Both the java application and the postgres are installed on the same machine.

At the beginning, the application is able to add in the order of 100 record per minute. Gradually (after several hours), it slows down to less than 10 records per minute. At this time, postgres processes take between 80-99% of CPU. When we reindex the database, the speed bumps up to about 30 records per minute. Now, postgres server takes between 50-70% CPU.

We have the following in the postgresql.conf :

max_fsm_pages = 500000

fsync = false

We certainly can not live with this kind of performance. I believe postgres should be able to handle much larger datasets but I can not point my finger as to what are we doing wrong. Can somebody please point me to the right direction.

With kind regards,

-- Shachindra Agarwal.

A few questions first. How are you loading the data? Are you using INSERT or COPY? Are you using a transaction, or are you autocommitting each row?

You really need a transaction, and preferably use COPY. Both can help performance a lot. (In some of the tests, single row inserts can be 10-100x slower than doing it in bulk.)

Also, it sounds like you have a foreign key issue. That as things fill up, the foreign key reference checks are slowing you down.
Are you using ANALYZE as you go? A lot of times when you only have <1000 rows a sequential scan is faster than using an index, and if you don't inform postgres that you have more rows, it might still use the old seqscan.

There are other possibilities, but it would be nice to know about your table layout, and possibly an EXPLAIN ANALYZE of the inserts that are going slow.


PS> I don't know if JDBC supports COPY, but it certainly should support transactions.

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