pgsql: Prevent lwlock dtrace probes from unnecessary work

Prevent lwlock dtrace probes from unnecessary work

If dtrace is compiled in but disabled, the lwlock dtrace probes still
evaluate their arguments. Since PostgreSQL 13, T_NAME(lock) does
nontrivial work, so it should be avoided if not needed. To fix, make
these calls conditional on the *_ENABLED() macro corresponding to each
probe.

Reviewed-by: Craig Ringer <craig(dot)ringer(at)enterprisedb(dot)com>
Discussion: https://www.postgresql.org/message-id/CAGRY4nwxKUS_RvXFW-ugrZBYxPFFM5kjwKT5O+0+Stuga5b4+Q@mail.gmail.com

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e48ce7ef0ef8de3d8e9e56be4d23d7830681b18b

Modified Files
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src/backend/storage/lmgr/lwlock.c | 39 ++++++++++++++++++++++++++-------------
1 file changed, 26 insertions(+), 13 deletions(-)