Re: Finalizing read stream users' flag choices
От | Andres Freund |
---|---|
Тема | Re: Finalizing read stream users' flag choices |
Дата | |
Msg-id | go7c2sudqg4pp7dsabsak4ajugti4f3tyqoweja5ihcjiw65dc@yh6wi4zqys23 обсуждение исходный текст |
Ответ на | Finalizing read stream users' flag choices (Melanie Plageman <melanieplageman@gmail.com>) |
Список | pgsql-hackers |
hi, On 2025-04-08 12:06:47 -0400, Melanie Plageman wrote: > And a somewhat related point, with buffered IO, READ_STREAM_SEQUENTIAL > disables prefetching to encourage OS readahead. I don't know if any > other users than sequential scan should do this. Worth adding that prefetches are only issued when io_method==sync and thus READ_STREAM_SEQUENTIAL only has an effect if io_method==sync. I suspect we should retire READ_STREAM_SEQUENTIAL in 19 or so: a) The sequential-ness detection has gotten smarter / more granular, reducing the need for forcing read_stream's hand. b) There are plenty cases where READ_STREAM_SEQUENTIAL *hurts* with seqscans and io_method==sync, e.g. if there are plenty pre-existing buffers in s_b. c) It doesn't have an effect with io_method != sync But it'll depend a bit on our experiences. Greetings, Andres Freund
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