postgres

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Fujii Masao 46d6e5f567 Display the time when the process started waiting for the lock, in pg_locks, take 2 This commit adds new column "waitstart" into pg_locks view. This column reports the time when the server process started waiting for the lock if the lock is not held. This information is useful, for example, when examining the amount of time to wait on a lock by subtracting "waitstart" in pg_locks from the current time, and identify the lock that the processes are waiting for very long. This feature uses the current time obtained for the deadlock timeout timer as "waitstart" (i.e., the time when this process started waiting for the lock). Since getting the current time newly can cause overhead, we reuse the already-obtained time to avoid that overhead. Note that "waitstart" is updated without holding the lock table's partition lock, to avoid the overhead by additional lock acquisition. This can cause "waitstart" in pg_locks to become NULL for a very short period of time after the wait started even though "granted" is false. This is OK in practice because we can assume that users are likely to look at "waitstart" when waiting for the lock for a long time. The first attempt of this patch (commit `3b733fcd04`) caused the buildfarm member "rorqual" (built with --disable-atomics --disable-spinlocks) to report the failure of the regression test. It was reverted by commit `890d2182a2`. The cause of this failure was that the atomic variable for "waitstart" in the dummy process entry created at the end of prepare transaction was not initialized. This second attempt fixes that issue. Bump catalog version. Author: Atsushi Torikoshi Reviewed-by: Ian Lawrence Barwick, Robert Haas, Justin Pryzby, Fujii Masao Discussion: https://postgr.es/m/a96013dc51cdc56b2a2b84fa8a16a993@oss.nttdata.com		5 years ago
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src	Display the time when the process started waiting for the lock, in pg_locks, take 2	5 years ago
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