Chris wrote:
Stut wrote:
Chris wrote:
Rob Adams wrote:
I have a query that I run using mysql that returns about 60,000 plus rows. It's been so large that I've just been testing it with a limit 0, 10000 (ten thousand) on the query. That used to take about 10 minutes to run, including processing time in PHP which spits out xml from the query. I decided to chunk the query down into 1,000 row increments, and tried that. The script processed 10,000 rows in 23 seconds! I was amazed! But unfortunately it takes quite a bit longer than 6*23 to process the 60,000 rows that way (1,000 at a time). It takes almost 8 minutes. I can't figure out why it takes so long, or how to make it faster. The data for 60,000 rows is about 120mb, so I would prefer not to use a temporary table. Any other suggestions? This is probably more a db issue than a php issue, but I thought I'd try here first.


Sounds like missing indexes or something.

Use explain: http://dev.mysql.com/doc/refman/4.1/en/explain.html

If that were the case I wouldn't expect limiting the number of rows returned to make a difference since the actual query is the same.

Actually it can. I don't think mysql does this but postgresql does take the limit/offset clauses into account when generating a plan.

http://www.postgresql.org/docs/current/static/sql-select.html#SQL-LIMIT

Not really relevant to the problem though :P

How many queries do you run with an order? But you're right, if there is no order by clause adding a limit probably will make a difference, but there must be an order by when you use limit to ensure the SQL engine doesn't give you the same rows in response to more than one of the queries.

-Stut

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