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From: Tom Lane <[email protected]>
To: =?iso-8859-2?Q?Pecs=F6k_J=E1n?= <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: Reading execution plan - first row time vs last row time
Date: Tue, 01 Oct 2024 10:43:52 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <AS1PR05MB91059DA7056B7C30EAE61AA59F772@AS1PR05MB9105.eurprd05.prod.outlook.com>
References: <AS1PR05MB91059DA7056B7C30EAE61AA59F772@AS1PR05MB9105.eurprd05.prod.outlook.com>

=?iso-8859-2?Q?Pecs=F6k_J=E1n?= <[email protected]> writes:
> We see significant difference in explain analyze Actual time in the first line of execution plan and Execution time in the last line of execution plan. What can be the reason?

The time reported for the top query node is just the time taken to
compute all the rows returned by the query.  It doesn't account
for what might be done with the data afterward.  A normal EXPLAIN
just drops that data on the floor, so there's not much time left
unaccounted-for.  But if you're writing the data into a table via
EXPLAIN CREATE TABLE AS, that I/O would be extra.

			regards, tom lane

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