Обсуждение: Dealing with large query results

Greetings,

I keep seeing reference to an 8K limit on query results.  So how to deal
with query results greater than 8K?  Am I under the wrong impression that
when you run a query from, say libpq, that each retch row is returned only
when you execute a fetchrow?  Or is the whole query stuffed in to a buffer
which has an 8K limit?

I have to deal with some queries that create a huge result, and/or doing
reports requires a large result set.  How can I deal with these larger results?

I'll probably get flamed for asking this one but, how can I step through a
table?  Hey, sometimes you just have to do it.

Thanks,
Matthew

Matthew Hagerty wrote:
>
> Greetings,
>
> I keep seeing reference to an 8K limit on query results.  So how to deal
> with query results greater than 8K?  Am I under the wrong impression that
> when you run a query from, say libpq, that each retch row is returned only
> when you execute a fetchrow?  Or is the whole query stuffed in to a buffer
> which has an 8K limit?

the current 8K limit is for queries (and unrelatedly single rows),
not query _results_

> I have to deal with some queries that create a huge result, and/or doing
> reports requires a large result set.  How can I deal with these larger results?

If you dont want to digest a huge result, you can do a

DECLARE CURSOR - FETCH -FETCH - FETCH - CLOSE CURSOR thing to get it in
pieces

(needs to be inside BEGIN TRANSACTION - END TRANSACTION)

> I'll probably get flamed for asking this one but, how can I step through a
> table?  Hey, sometimes you just have to do it.

See above.

Actually postgres is quite happy to return gigabytes of data, if you
have
the resources (disk space, memory, time ;)

--------------
Hannu

On Mon, 8 Feb 1999, Matthew Hagerty wrote:

> Greetings,
>
> I keep seeing reference to an 8K limit on query results.  So how to deal
> with query results greater than 8K?  Am I under the wrong impression that
> when you run a query from, say libpq, that each retch row is returned only
> when you execute a fetchrow?  Or is the whole query stuffed in to a buffer
> which has an 8K limit?

No. The entire result is returned.

The 8k limit is the block size used to store data on disk. The limit
affects the size of each row, not the query results.

--
       Peter T Mount peter@retep.org.uk
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