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From: David Rowley <dgrowleyml@gmail.com>
To: Nazir Bilal Yavuz <byavuz81@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Cc: Andres Freund <andres@anarazel.de>
Cc: Melanie Plageman <melanieplageman@gmail.com>
Subject: Re: Streaming I/O, vectored I/O (WIP)
Date: Wed, 24 Apr 2024 14:32:09 +1200
Message-ID: <CAApHDvr9Un-XpDr_+AFdOGM38O2K8SpfoHimqZ838gguTGYBiQ@mail.gmail.com> (raw)
In-Reply-To: <CAN55FZ1yGvCzCW_aufu83VimdEYHbG_zuOY3J9JL-nBptyJyKA@mail.gmail.com>
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	<56bc4ac4-9a9e-4f28-af1e-b6d537bd9a5e@iki.fi>
	<CA+hUKG+2mMiyJEDV-rNb5q__x9VJW5p8oJpGn9ZpovbyoVe1VA@mail.gmail.com>
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	<98f01395-fc60-4d50-89c9-fc3011fa2a45@iki.fi>
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	<d1eb996b-423a-4bcd-bce4-75f5daa12ffa@iki.fi>
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	<CAN55FZ1yGvCzCW_aufu83VimdEYHbG_zuOY3J9JL-nBptyJyKA@mail.gmail.com>

I've attached a patch with a few typo fixes and what looks like an
incorrect type for max_ios. It's an int16 and I think it needs to be
an int. Doing "max_ios = Min(max_ios, PG_INT16_MAX);" doesn't do
anything when max_ios is int16.

David

Attachments:


read_stream_fixes.patch (text/plain, 1.6K) download
diff --git a/src/backend/storage/aio/read_stream.c b/src/backend/storage/aio/read_stream.c
index 634cf4f0d1..74b9bae631 100644
--- a/src/backend/storage/aio/read_stream.c
+++ b/src/backend/storage/aio/read_stream.c
@@ -26,12 +26,12 @@
  *
  * B) I/O is necessary, but fadvise is undesirable because the access is
  * sequential, or impossible because direct I/O is enabled or the system
- * doesn't support advice.  There is no benefit in looking ahead more than
- * io_combine_limit, because in this case only goal is larger read system
+ * doesn't support fadvise.  There is no benefit in looking ahead more than
+ * io_combine_limit, because in this case the only goal is larger read system
  * calls.  Looking further ahead would pin many buffers and perform
  * speculative work looking ahead for no benefit.
  *
- * C) I/O is necesssary, it appears random, and this system supports fadvise.
+ * C) I/O is necessary, it appears random, and this system supports fadvise.
  * We'll look further ahead in order to reach the configured level of I/O
  * concurrency.
  *
@@ -418,7 +418,7 @@ read_stream_begin_relation(int flags,
 	ReadStream *stream;
 	size_t		size;
 	int16		queue_size;
-	int16		max_ios;
+	int			max_ios;
 	int			strategy_pin_limit;
 	uint32		max_pinned_buffers;
 	Oid			tablespace_id;
@@ -447,6 +447,8 @@ read_stream_begin_relation(int flags,
 		max_ios = get_tablespace_maintenance_io_concurrency(tablespace_id);
 	else
 		max_ios = get_tablespace_io_concurrency(tablespace_id);
+
+	/* Cap to INT16_MAX to avoid overflowing below */
 	max_ios = Min(max_ios, PG_INT16_MAX);
 
 	/*


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  Cc: dgrowleyml@gmail.com, byavuz81@gmail.com, thomas.munro@gmail.com, hlinnaka@iki.fi, dilipbalaut@gmail.com, robertmhaas@gmail.com, andres@anarazel.de, melanieplageman@gmail.com
  Subject: Re: Streaming I/O, vectored I/O (WIP)
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