Make backend query execution interruptible. #454
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The compatibility macros mess up some postgresql headers, yielding compilation failures. pglogical doesn't use affected headers now, so there's no live bug. The next change will add use of such a header.
https://www.postgresql.org/docs/current/libpq-copy.html directs COPY callers to do this. By not doing this, pglogical risked ignoring a late failure in the COPY FROM query. This change unblocks replacing PQexec() with PQsendQuery(). The former silently discards any prior query result, but the latter fails. Since plain PQgetResult() blocks without responding to interrupts, import the PostgreSQL v17 libpq/libpq-be-fe-helpers.h for its interruptible helper. Adapt the header to v9.4+ with PG_VERSION_NUM conditions and changing WL_EXIT_ON_PM_DEATH to explicit proc_exit(). Divide the header into two include-guarded regions, one for v16 content and one for v17+ content.
This prevents v15+ DROP DATABASE hanging when a pglogical process waits inside one of these calls. (See 2ndQuadrant#418 for fixes of that symptom under different conditions.) In all versions, it brings responsiveness of these calls to query cancel, backend termination, and fast shutdown.
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This prevents v15+ DROP DATABASE hanging when a pglogical process waits inside
one of these calls. (See #418
for fixes of that symptom under different conditions.) In all versions, it
brings responsiveness of these calls to query cancel, backend termination, and
fast shutdown.
Future work should include adopting libpqsrv_connect_params(). I didn't bundle
that in this pull request, because that function doesn't support all the
connection parameters that PQconnectdbParams() supports. Specifically, since
libpqsrv_connect_params() wraps PQconnectStartParams(), it has the limitations
discussed in
https://postgr.es/m/flat/CA%2Bmi_8YyGKA9dWELu63e%3DKL2oN-%2BFe4uca4EtFfb6uQD4Up8pw%40mail.gmail.com.
Future work should also bring interruptibility to calls of
PQgetCopyData(async=false), PQputCopyData(), and PQputCopyEnd().
No new test failures in:
When v17 support appears, compat17/pglogical_compat.h can just #include
"libpq/libpq-be-fe-helpers.h" rather than use the local copy.