From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
Cc: | alexandros_e <alexandros(dot)ef(at)gmail(dot)com>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: C++, Postgres , libpqxx huge query |
Date: | 2014-05-04 14:34:10 |
Message-ID: | 23853.1399214050@sss.pgh.pa.us |
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Lists: | pgsql-general |
Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> On 2014-05-04 01:57:43 -0700, alexandros_e wrote:
>> I have to execute an SQL query to Postgres by the following code. The query
>> returns a huge number of rows (40M or more) and has 4 integer fields: When I
>> use a workstation with 32Gb everything works but on a 16Gb workstation the
>> query is very slow (due to swapping I guess). Is there any way to tell the
>> C++ to load rows at batches, without waiting the entire dataset? With Java I
>> never had these issues before, due to the probably better JDBC driver.
> Try looking into either using a serverside cursor or COPY.
Another possibility is libpq's recently-introduced row-at-a-time mode:
http://www.postgresql.org/docs/9.3/static/libpq-single-row-mode.html
though I'm not sure how effectively that's supported by libpqxx.
regards, tom lane
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