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From: Bagga, Rishu <[email protected]>
To: Thomas Munro <[email protected]>
To: Heikki Linnakangas <[email protected]>
Cc: pgsql-hackers <[email protected]>
Subject: Re: SLRUs in the main buffer pool, redux
Date: Sat, 17 Sep 2022 00:41:14 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+hUKGKCkbtOutcz5M8Z=0pgAkwdiR57Lxk7803rGsgiBNST6w@mail.gmail.com>
References: <CA+hUKGKAYze99B-jk9NoMp-2BDqAgiRC4oJv+bFxghNgdieq8Q@mail.gmail.com>
	<[email protected]>
	<CA+hUKG+qzHB-mY3kym7JCQ-SbiO88hhiWKkUCfLMQmm7CbaCBw@mail.gmail.com>
	<CA+hUKGKCkbtOutcz5M8Z=0pgAkwdiR57Lxk7803rGsgiBNST6w@mail.gmail.com>

Hi Thomas,

While I was working on adding the page headers to SLRU pages on your patch, I came across this code where it seems like "MultiXactIdToMemberPage" is mistakenly being used instead of MultiXactIdToOffsetPage in the TrimMultiXact function.

Below is the area of concern in the patch:

@@ -2045,14 +1977,7 @@ TrimMultiXact(void)
 	oldestMXactDB = MultiXactState->oldestMultiXactDB;
 	LWLockRelease(MultiXactGenLock);
 
-	/* Clean up offsets state */
-	LWLockAcquire(MultiXactOffsetSLRULock, LW_EXCLUSIVE);
-
-	/*
-	 * (Re-)Initialize our idea of the latest page number for offsets.
-	 */
-	pageno = MultiXactIdToOffsetPage(nextMXact);
-	MultiXactOffsetCtl->shared->latest_page_number = pag0eno;
+	pageno = MXOffsetToMemberPage(offset);


Let us know if I am missing something here or if it is an error.

Sincerely,

Rishu Bagga (Amazon Web Services)

On 9/16/22, 5:37 PM, "Thomas Munro" <[email protected]> wrote:

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    Rebased, debugged and fleshed out a tiny bit more, but still with
    plenty of TODO notes and questions.  I will talk about this idea at
    PGCon, so I figured it'd help to have a patch that actually applies,
    even if it doesn't work quite right yet.  It's quite a large patch but
    that's partly because it removes a lot of lines...

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