Fix permanent memory leak in autovacuum launcher
get_database_list was uselessly allocating its output data, along some created along the way, in a permanent memory context. This didn't matter when autovacuum was a single, short-lived process, but now that the launcher is permanent, it shows up as a permanent leak. To fix, make get_database list allocate its output data in the caller's context, which is in charge of freeing it when appropriate; and the memory leaked by heap_beginscan et al is allocated in a throwaway transaction context.
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@ -1754,6 +1754,9 @@ autovac_balance_cost(void)
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* get_database_list
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* Return a list of all databases found in pg_database.
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*
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* The list and associated data is allocated in the caller's memory context,
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* which is in charge of ensuring that it's properly cleaned up afterwards.
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*
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* Note: this is the only function in which the autovacuum launcher uses a
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* transaction. Although we aren't attached to any particular database and
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* therefore can't access most catalogs, we do have enough infrastructure
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@ -1766,6 +1769,10 @@ get_database_list(void)
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Relation rel;
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HeapScanDesc scan;
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HeapTuple tup;
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MemoryContext resultcxt;
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/* This is the context that we will allocate our output data in */
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resultcxt = CurrentMemoryContext;
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/*
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* Start a transaction so we can access pg_database, and get a snapshot.
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@ -1777,9 +1784,6 @@ get_database_list(void)
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StartTransactionCommand();
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(void) GetTransactionSnapshot();
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/* Allocate our results in AutovacMemCxt, not transaction context */
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MemoryContextSwitchTo(AutovacMemCxt);
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rel = heap_open(DatabaseRelationId, AccessShareLock);
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scan = heap_beginscan(rel, SnapshotNow, 0, NULL);
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@ -1787,6 +1791,15 @@ get_database_list(void)
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{
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Form_pg_database pgdatabase = (Form_pg_database) GETSTRUCT(tup);
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avw_dbase *avdb;
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MemoryContext oldcxt;
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/*
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* Allocate our results in the caller's context, not the transaction's.
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* We do this inside the loop, and restore the original context at the
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* end, so that leaky things like heap_getnext() are not called in a
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* potentially long-lived context.
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*/
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oldcxt = MemoryContextSwitchTo(resultcxt);
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avdb = (avw_dbase *) palloc(sizeof(avw_dbase));
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@ -1797,6 +1810,7 @@ get_database_list(void)
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avdb->adw_entry = NULL;
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dblist = lappend(dblist, avdb);
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MemoryContextSwitchTo(oldcxt);
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}
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heap_endscan(scan);
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