Re: BgBufferSync(): clarification about reusable_buffers variable
| От | Xuneng Zhou |
|---|---|
| Тема | Re: BgBufferSync(): clarification about reusable_buffers variable |
| Дата | |
| Msg-id | CABPTF7VRmzTnpBZqku21hjt-1r_E9fHV+jNMOSKNKW9xBQt3_Q@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: BgBufferSync(): clarification about reusable_buffers variable (Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>) |
| Ответы |
Re: BgBufferSync(): clarification about reusable_buffers variable
|
| Список | pgsql-hackers |
Hi, tks for working on this. I had a chance to look at this while googling BgBufferSync function.
I also think tha reusable_buffers keep track of the number of reusable
buffers. BgBufferSync() calls SyncOneBuffer() with skip_recently_used
= true. In that case, if SyncOneBuffer() finds the buffer with
refcount or usage_count non-zero, it just unlocks the header and
returns. Hence when called from BgBufferSync(), SyncOneBuffer() would
write a buffer only when it is not used. Hence the result would be 0
or BUF_REUSABLE or BUF_REUSABLE | BUF_WRITTEN. It can never be just
BUF_WRITTEN.
Agrees. For this call stack, if skip_recently_used is set to be true, sync_state cannot be BUF_WRITTEN alone.
I guess, a patch like the one attached will be more readable and clear.
I'm new to this part of code, and I found the patch version seems to be more straightforward and less prone to misinterpretation.
I ran pgbench for 5 minutes with this patch applied and didn't see the
Assert failing. But I don't think that's a good enough test to cover
all scenarios.
The patch LGTM.
--
Best Wishes,
Ashutosh Bapat
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