pgsql: Have walsenders participate in procsignal infrastructure.

Have walsenders participate in procsignal infrastructure.

The non-participation in procsignal was a problem for both changes in
master, e.g. parallelism not working for normal statements run in
walsender backends, and older branches, e.g. recovery conflicts and
catchup interrupts not working for logical decoding walsenders.

This commit thus replaces the previous WalSndXLogSendHandler with
procsignal_sigusr1_handler. In branches since db0f6cad48 that can
lead to additional SetLatch calls, but that only rarely seems to make
a difference.

Author: Andres Freund
Reviewed-By: Michael Paquier
Discussion: https://postgr.es/m/20170421014030.fdzvvvbrz4nckrow@alap3.anarazel.de
Backpatch: 9.4, earlier commits don't seem to benefit sufficiently

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b3d5b6833f460debde53a122709c3deb07056561

Modified Files
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src/backend/replication/walsender.c | 14 +-------------
1 file changed, 1 insertion(+), 13 deletions(-)