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Keep profile and history data in shared memory #66

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Keep profile and history data in shared memory #66

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49ff16c
Keep profile and history data in shared memory
Dec 27, 2022
ef33592
Resolve clang warning regarding to variable initialization
Feb 1, 2023
3bfb23d
Fix estimated size for profile hash table
maksm90 Feb 10, 2023
08b7e8c
Refactoring: s/pgws_hash/pgws_profile_hash/ s/pgws_hash_lock/pgws_pr…
maksm90 Feb 10, 2023
f0b62aa
Refine FIXME in collector's loop over ProcArray
maksm90 Feb 10, 2023
9a69965
Add TODO item to reduce contention of ProcArrayLock
maksm90 Feb 10, 2023
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11 changes: 10 additions & 1 deletion collector.c
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Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,16 @@ probe_waits(const bool write_history, const bool write_profile)
if (write_history)
LWLockAcquire(pgws_history_lock, LW_EXCLUSIVE);

/* Iterate PGPROCs under shared lock */
/*
* Iterate PGPROCs under shared lock.
*
* TODO:
* ProcArrayLock is heavy enough and in current case we might perform the
* non-trivial deallocation routine for profile hash table under this lock.
* Therefore to reduce possible contention it's worth to segregate the logic
* of PGPROCs iteration under ProcArrayLock and storing results to profile
* and/or history under corresponding another lock.
*/
LWLockAcquire(ProcArrayLock, LW_SHARED);
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Why do we take ProcArrayLock anyway? What concurrent operations does it prevent?
I don't think that blocking ProcArrayAdd and ProcArrayRemove buys us anything. We are not iterating over the procArray, but over allProcs. And we don't need the lock to read PGPROC.pid and wait_event_info.

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Yes, you are right. In current case when we verify slot validity also via non-zero wait_event_info value we might omit acquisition of this lock. This is mostly inherited from previous implementation.

for (int i = 0; i < ProcGlobal->allProcCount; i++)
{
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