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psql: Abort connection when using \syncpipeline after COPY TO/FROM

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When the backend reads COPY data, it ignores all sync messages, as per
c01641f8ae.  With psql pipelines, it is possible to manually send sync
messages with \sendpipeline which leaves the frontend in an
unrecoverable state as the backend will not send the necessary
ReadyForQuery message that is expected to feed psql result consumption
logic.

It could be possible to artificially reduce the piped_syncs and
requested_results, however libpq's state would still have queued sync
messages in its command queue, and the only way to consume those without
directly calling pqCommandQueueAdvance() is to process ReadyForQuery
messages that won't be sent since the backend ignores these.  Perhaps
this could be improved in the future, but I am not really excited about
introducing this amount of complications in libpq to manipulate the
message queues without a better use case to support it.

Hence, this patch aborts the connection if we detect excessive sync
messages after a COPY in a pipeline to avoid staying in an inconsistent
protocol state, which is the best thing we can do with pipelines in
psql for now.  Note that this change does not prevent wrapping a set
of queries inside a block made of \startpipeline and \endpipeline, only
the use of \syncpipeline for a COPY.

Reported-by: Nikita Kalinin <n.kalinin@postgrespro.ru>
Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Discussion: https://postgr.es/m/18944-8a926c30f68387dd@postgresql.org
This commit is contained in:
Michael Paquier
2025-06-04 09:01:29 +09:00
parent 58fbfde152
commit 7f3381c7ee
2 changed files with 35 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
src/bin/psql/common.c
View File

@ -1867,6 +1867,21 @@ ExecQueryAndProcessResults(const char *query,
{
FILE *copy_stream = NULL;
if (pset.piped_syncs > 1)
{
/*
* When reading COPY data, the backend ignores sync messages
* and will not send a matching ReadyForQuery response. Even
* if we adjust piped_syncs and requested_results, it is not
* possible to salvage this as the sync message would still be
* in libpq's command queue and we would be stuck in a busy
* pipeline state. Thus, we abort the connection to avoid
* this state.
*/
pg_log_info("\\syncpipeline after COPY is not supported, aborting connection");
exit(EXIT_BADCONN);
}
/*
* For COPY OUT, direct the output to the default place (probably
* a pager pipe) for \watch, or to pset.copyStream for \copy,

22
src/bin/psql/t/001_basic.pl
View File

@ -513,15 +513,33 @@ SELECT 'val1' \\bind \\sendpipeline
qr/server closed the connection unexpectedly/,
'protocol sync loss in pipeline: bind COPY, SELECT, sync and getresult');
# This time, test without the \getresults.
# This time, test without the \getresults and \syncpipeline.
psql_fails_like(
$node,
qq{\\startpipeline
COPY psql_pipeline FROM STDIN;
SELECT 'val1';
\\syncpipeline
\\endpipeline},
qr/server closed the connection unexpectedly/,
'protocol sync loss in pipeline: COPY, SELECT and sync');
# Tests sending a sync after a COPY TO/FROM. These abort the connection
# from the frontend.
psql_fails_like(
$node,
qq{\\startpipeline
COPY psql_pipeline FROM STDIN;
\\syncpipeline
\\endpipeline},
qr/\\syncpipeline after COPY is not supported, aborting connection/,
'sending sync after COPY FROM');
psql_fails_like(
$node,
qq{\\startpipeline
COPY psql_pipeline TO STDOUT;
\\syncpipeline
\\endpipeline},
qr/\\syncpipeline after COPY is not supported, aborting connection/,
'sending sync after COPY TO');
done_testing();