November 29th, 2017 by depesz | Tags: , , | No comments »
Did it help? If yes - maybe you can help me?

Bricklen Anderson reported a problem with explains that were using parallel processing.

TL;DR: in case of parallel plans make “inclusive" and “exclusive" be wall-clock times, and not “how much time CPU did spend on it".

The problem can be seen in here:

and in here:

You can see, in first one, that time in partial aggregate step (#3) is actually longer than total time of the query. This is/was because of parallel processing.

Similarly in second plan, in step 16 times are totally abstract.

Based on the problem I released new version of Pg::Explain library, which solves this problem (and also fixes anonymization of elements in parallel plans).

With this new version, we have new explains:

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