Re: BUG #18259: Assertion in ExtendBufferedRelLocal() fails after no-space-left condition

When I debugged the ExtendBufferedRelLocal(), I found a repeated assignment
to existing_hdr.
So I fixed this small issue with the previous v2 patch together with the
attached v3 patch.

tender wang <tndrwang@gmail.com> 于2023年12月27日周三 17:08写道：

>
>
> Alexander Lakhin <exclusion@gmail.com> 于2023年12月27日周三 15:00写道：
>
>> Hello tender wang,
>>
>> 26.12.2023 19:55, tender wang write:
>>
>> I tried to analyze the issue, and I found that it might be caused by this
>> commit:
>> commit dad50f677c42de207168a3f08982ba23c9fc6720
>>        bufmgr: Acquire and clean victim buffer separately
>>
>>
>> Thanks for looking into it!
>>
>> ...
>>>
>>> With debug logging added in this code within ExtendBufferedRelLocal():
>>>>         if (found)
>>>>         {
>>>>             BufferDesc *existing_hdr =
>>>> GetLocalBufferDescriptor(hresult->id);
>>>>             uint32      buf_state;
>>>>
>>>>             UnpinLocalBuffer(BufferDescriptorGetBuffer(victim_buf_hdr));
>>>>
>>>>             existing_hdr = GetLocalBufferDescriptor(hresult->id);
>>>>             PinLocalBuffer(existing_hdr, false);
>>>>             buffers[i] = BufferDescriptorGetBuffer(existing_hdr);
>>>>
>>>>             buf_state = pg_atomic_read_u32(&existing_hdr->state);
>>>>             Assert(buf_state & BM_TAG_VALID);
>>>>             Assert(!(buf_state & BM_DIRTY));
>>>>             buf_state &= BM_VALID;
>>>>             pg_atomic_unlocked_write_u32(&existing_hdr->state,
>>>> buf_state);
>>>> ...
>>>> I see that it reached for the second INSERT (and NOSPC error) with
>>>> existing_hdr->state == 0x2040000, but for the third INSERT I observe
>>>> state == 0x0.
>>>>
>>>>
>> I wonder, if "buf_state &= BM_VALID" is a typo here, maybe it supposed to
>> be
>> "buf_state &= ~BM_VALID" as in ExtendBufferedRelShared()...
>>
>
> Yeah, that's true.  I analyze this issue again, and I think the root cause
> is the " buf_state &= BM_VALID" .
> In my report issue, buf_state & BM_VALID is true, but buf_state &
> BM_TAG_VALID is false. This situation is impossible.
> It can't happen that the data in the local buffer pool is valid, but
> LocalBufHash has no entry.
>
> I modified v1 patch, and attached v2 patch should fix the above issues.
>
> Best regards,
>> Alexander
>>
>