Re: SLRUs in the main buffer pool, redux

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" <thomas.munro@gmail.com> 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...