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Allow \watch queries to stop on minimum rows returned

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When running a repeat query with \watch in psql, it can be
helpful to be able to stop the watch process when the query
no longer returns the expected amount of rows.  An example
would be to watch for the presence of a certain event in
pg_stat_activity and stopping when the event is no longer
present, or to watch an index creation and stop when the
index is created.

This adds a min_rows=MIN parameter to \watch which can be
set to a non-negative integer, and the watch query will
stop executing when it returns less than MIN rows.

Author: Greg Sabino Mullane <htamfids@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/CAKAnmmKStATuddYxP71L+p0DHtp9Rvjze3XRoy0Dyw67VQ45UA@mail.gmail.com
This commit is contained in:
Daniel Gustafsson
2023-08-29 11:30:11 +02:00
parent 95fff2abee
commit f347ec76e2
6 changed files with 72 additions and 15 deletions
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4
src/bin/psql/help.c
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@@ -200,7 +200,9 @@ slashUsage(unsigned short int pager)
HELP0(" \\gset [PREFIX] execute query and store result in psql variables\n");
HELP0(" \\gx [(OPTIONS)] [FILE] as \\g, but forces expanded output mode\n");
HELP0(" \\q quit psql\n");
HELP0(" \\watch [[i=]SEC] [c=N] execute query every SEC seconds, up to N times\n");
HELP0(" \\watch [[i=]SEC] [c=N] [m=MIN]\n");
HELP0(" execute query every SEC seconds, up to N times\n");
HELP0(" stop if less than MIN rows are returned\n");
HELP0("\n");
HELP0("Help\n");