On 2021-02-05 18:49, Fujii Masao wrote:
On 2021/02/05 0:03, torikoshia wrote:
On 2021-02-03 11:23, Fujii Masao wrote:
64-bit fetches are not atomic on some platforms. So spinlock is
necessary when updating "waitStart" without holding the partition
lock? Also GetLockStatusData() needs spinlock when reading
"waitStart"?
Also it might be worth thinking to use 64-bit atomic operations like
pg_atomic_read_u64(), for that.
Thanks for your suggestion and advice!
In the attached patch I used pg_atomic_read_u64() and
pg_atomic_write_u64().
waitStart is TimestampTz i.e., int64, but it seems pg_atomic_read_xxx
and pg_atomic_write_xxx only supports unsigned int, so I cast the
type.
I may be using these functions not correctly, so if something is
wrong, I would appreciate any comments.
About the documentation, since your suggestion seems better than v6, I
used it as is.
Thanks for updating the patch!
+ if (pg_atomic_read_u64(&MyProc->waitStart) == 0)
+ pg_atomic_write_u64(&MyProc->waitStart,
+
pg_atomic_read_u64((pg_atomic_uint64 *) &now));
pg_atomic_read_u64() is really necessary? I think that
"pg_atomic_write_u64(&MyProc->waitStart, now)" is enough.
+ deadlockStart = get_timeout_start_time(DEADLOCK_TIMEOUT);
+ pg_atomic_write_u64(&MyProc->waitStart,
+ pg_atomic_read_u64((pg_atomic_uint64 *)
&deadlockStart));
Same as above.
+ /*
+ * Record waitStart reusing the deadlock timeout timer.
+ *
+ * It would be ideal this can be synchronously done with
updating
+ * lock information. Howerver, since it gives performance
impacts
+ * to hold partitionLock longer time, we do it here
asynchronously.
+ */
IMO it's better to comment why we reuse the deadlock timeout timer.
proc->waitStatus = waitStatus;
+ pg_atomic_init_u64(&MyProc->waitStart, 0);
pg_atomic_write_u64() should be used instead? Because waitStart can be
accessed concurrently there.
I updated the patch and addressed the above review comments. Patch
attached.
Barring any objection, I will commit this version.
Thanks for modifying the patch!
I agree with your comments.
BTW, I ran pgbench several times before and after applying
this patch.
The environment is virtual machine(CentOS 8), so this is
just for reference, but there were no significant difference
in latency or tps(both are below 1%).
Regards,
--
Atsushi Torikoshi
