Apparently these markers cause the modules to not link correctly in some
platforms, at least per buildfarm member indri; moreover, this code is
only used in modules that don't have a translation. If we someday add
i18n support to contrib/ it might be worth revisiting this.
Commit 61461a300c introduced new functions to libpq for cancelling
queries. This commit introduces a helper function that backend-side
libraries and extensions can use to invoke those. This function takes a
timeout and can itself be interrupted while it is waiting for a cancel
request to be sent and processed, instead of being blocked.
This replaces the usage of the old functions in postgres_fdw and dblink.
Finally, it also adds some test coverage for the cancel support in
postgres_fdw.
Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/CAGECzQT_VgOWWENUqvUV9xQmbaCyXjtRRAYO8W07oqashk_N+g@mail.gmail.com
This replaces dblink's blocking libpq calls, allowing cancellation and
allowing DROP DATABASE (of a database not involved in the query). Apart
from explicit dblink_cancel_query() calls, dblink still doesn't cancel
the remote side. The replacement for the blocking calls consists of
new, general-purpose query execution wrappers in the libpqsrv facility.
Out-of-tree extensions should adopt these. Use them in postgres_fdw,
replacing a local implementation from which the libpqsrv implementation
derives. This is a bug fix for dblink. Code inspection identified the
bug at least thirteen years ago, but user complaints have not appeared.
Hence, no back-patch for now.
Discussion: https://postgr.es/m/20231122012945.74@rfd.leadboat.com
Currently dblink and postgres_fdw don't process interrupts during connection
establishment. Besides preventing query cancellations etc, this can lead to
undetected deadlocks, as global barriers are not processed.
Libpqwalreceiver in contrast, processes interrupts during connection
establishment. The required code is not trivial, so duplicating it into
additional places does not seem like a good option.
These aforementioned undetected deadlocks are the reason for the spate of CI
test failures in the FreeBSD 'test_running' step.
For now the helper library is just a header, as it needs to be linked into
each extension using libpq, and it seems too small to be worth adding a
dedicated static library for.
The conversion to the helper are done in subsequent commits.
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/20220925232237.p6uskba2dw6fnwj2@awork3.anarazel.de
Alvaro Herrera
Noah Misch
Bruce Momjian
Andres Freund