Re: EXPLAIN: showing ReadStream / prefetch stats

On 3/16/26 18:49, Tomas Vondra wrote:
> On 3/16/26 18:14, Melanie Plageman wrote:
>> ...
>>
>> I see a couple more issues with the counting in read_stream.c.
>>
>> You are double-counting stalls for synchronous IO. You increment
>> stalls in read_stream_next_buffer() but we actually execute
>> synchronous IO in WaitReadBuffers and return needed_wait as true,
>> which will count a stall again.
>>
>> You are not counting fast path IOs because those don't go through
>> read_stream_start_pending_read() and instead are started directly by
>> StartReadBuffer() in read_stream_next_buffer(). Simple diff attached
>> should fix this.
>>
>> Also, per worker stats are not displayed when BUFFERS false is passed
>> even with IO true because of a small oversight. I fixed it in the
>> attached diff.
>>
>
> Thanks!
>

Here's a v2 with your fixes merged. No other changes.

regards

--
Tomas Vondra