PROC_VACUUM_FOR_WRAPAROUND doesn't work expectedly

I found autovacuum can be canceled by blocked backends even if the vacuum
is for preventing XID wraparound in 8.3.0 and HEAD. Autovacuum sets
PROC_VACUUM_FOR_WRAPAROUND flag just before vacuum, but the flag will be
cleared at the beginning of vacuum; PROC_VACUUM_FOR_WRAPAROUND is not set
during the vacuum.

The sequence is below:
vacuum()-> CommitTransactionCommand()    -> ProcArrayEndTransaction()        -> proc->vacuumFlags &=
~PROC_VACUUM_STATE_MASK;->vacuum_rel()
 

PROC_VACUUM_STATE_MASK is defined as (0x0E), that is including
PROC_VACUUM_FOR_WRAPAROUND (0x08). The wraparound flag is cleared
before vacuum tasks.

I tried to make a patch to exclude PROC_VACUUM_FOR_WRAPAROUND
from PROC_VACUUM_STATE_MASK and make autovacuum workers to clear
PROC_VACUUM_FOR_WRAPAROUND by themselves. Is it a reasonable solution?


Index: src/backend/postmaster/autovacuum.c
===================================================================
--- src/backend/postmaster/autovacuum.c    (HEAD)
+++ src/backend/postmaster/autovacuum.c    (working copy)
@@ -2163,6 +2163,12 @@        PG_END_TRY();        /* the PGPROC flags are reset at the next end of transaction */
+        if (tab->at_wraparound)
+        {
+            LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
+            MyProc->vacuumFlags &= ~PROC_VACUUM_FOR_WRAPAROUND;
+            LWLockRelease(ProcArrayLock);
+        }        /* be tidy */        pfree(tab);
Index: src/include/storage/proc.h
===================================================================
--- src/include/storage/proc.h    (HEAD)
+++ src/include/storage/proc.h    (working copy)
@@ -45,7 +45,7 @@#define        PROC_VACUUM_FOR_WRAPAROUND 0x08        /* set by autovac only *//* flags reset at
EOXact*/
 
-#define        PROC_VACUUM_STATE_MASK (0x0E)
+#define        PROC_VACUUM_STATE_MASK (PROC_IN_VACUUM | PROC_IN_ANALYZE)/* * Each backend has a PGPROC struct in
sharedmemory.  There is also a list of
 

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center