Re: setFetchSize() [Viruschecked] [Viruschecked] - Mailing list pgsql-jdbc

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On Thu, 17 Jul 2003 13:20:49 -0400, Dmitry Tkach wrote:

Hello Dmitry,

>>that's exactly what the driver is doing if you do a setFetchSize(10).
>>Nevertheless, it won't solve the problem of the server eating HUGE amounts of memory if you do a "declare foo cursor
forselect * from myhugetable". It seems  
>>like postgresql locks all rows (or even copies them around in memory) until the connection drops again.
>>
>>
>At least one of your two statements above must be wrong :-)
>Either it is not the same thing the driver is doing with setFetchSize()
>or you are mistaken about the server eating memory and locking rows and
>copying them around when you use cursors.
>
>I have never used setFetchSize () (never even seen a driver version
>where it was implemented), so, I can't tell you which one is wrong, but
>I have been using this cursor approach for almost two years now, in a
>huge application, making queries that return tens of millions of rows,
>and have never had any locking or memory problems that I could attribute
>to a bug in my java code...

That's exactly like I see it here (Windows AND Linux, Version 7.3.3).
The setFetchSize-code was analyzed and party improved by me (my patch didn't get accepted, sigh) to be switched on and
offby an URL parameter. So I clearly understand what it does. And that's what I told you. 
But: If I enter into psql and put one of the queries into it with a "declare test cursor for" infront of it, postgres
startsincreasing it's memory footprint, and it ends this only if I do a \c anotherDataBase. The same thing I
experiencedin my Java apps. I even had problems with the shared memory size, so I had to increase that to unreasonable
valuesbeyond 4096 (at least it's unreasonable for ME). The whole database is 300 MB on the harddisk, but some specific
queriesstart to hug over 1 GB of memory. That's what I don't understand. And if the query is executed without the
cursor,the memory footprint stays within 10 MB! 
Maybe one of the hackers can explain this... The configuration is standard, only shared buffers is raised, otherwise
thequeries tend to break just too soon. 

tia

Patric

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