From: Tom Lane <tgl@sss.pgh.pa.us>
To: =?UTF-8?B?QnJpY2UgQW5kcsOp?= <brice@famille-andre.be>
cc: pgsql-sql@postgresql.org
Subject: Re: Memory exhaustion on large query
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Comments: In-reply-to =?UTF-8?B?QnJpY2UgQW5kcsOp?= <brice@famille-andre.be>
	message dated "Sun, 12 Dec 2021 19:25:49 +0100"
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Date: Sun, 12 Dec 2021 13:43:51 -0500
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=?UTF-8?B?QnJpY2UgQW5kcsOp?= <brice@famille-andre.be> writes:
> The content of the table is so huge that, if PQsendQueryPrepared retrieves
> all data, or if postgresql engine is creating temp file with all data, the
> query cannot succeed (I have no enough RAM or disk space to copy the whole
> data). But I was expecting that using PQsendQueryPrepared and PQgetResult
> would avoid this by returning one result at a time.

You're confusing asynchronous mode with single-row mode.  Async mode,
per se, doesn't change memory consumption; it just lets you do something
else while waiting for the query result.  You are (I suppose) missing
a call to PQsetSingleRowMode --- see

https://www.postgresql.org/docs/current/libpq-single-row-mode.html

			regards, tom lane