pgsql: injection_points: Tweak variable-numbered stats to work with pen

injection_points: Tweak variable-numbered stats to work with pending data

As coded, the module was not using pending entries to store its data
locally before doing a flush to the central dshash with a timed
pgstat_report_stat() call.  Hence, the flush callback was defined, but
finished by being not used.  As a template, this is more efficient than
the original logic of updating directly the shared memory entries as
this reduces the interactions that need to be done with the pgstats
hash table in shared memory.

injection_stats_flush_cb() was also missing a pgstat_unlock_entry(), so
add one, while on it.

Reviewed-by: Bertrand Drouvot
Discussion: https://postgr.es/m/Z3JbLhKFFm6kKfT8@ip-10-97-1-34.eu-west-3.compute.internal

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b757abefc0419c9b742222e1dfe70c73aff67364

Modified Files
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src/test/modules/injection_points/injection_stats.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)