bug? autovacuum is not launched even if autovacuum_freeze_max_age is reached

Hi,

In HEAD, when autovacuum is disabled, autovacuum process is not
launched forcibly to prevent XID wraparound even if we go through
autovacuum_freeze_max_age. This seems to be because
ShmemVariableCache->xidVacLimit is not initialized (i.e.,
SetTransactionIdLimit() is not called) until VACUUM is performed.

OTOH, in older version, ShmemVariableCache->xidVacLimit is always
initialized when backend updates the flat database file, and then
autovacuum process seems to be launched forcibly as expected.

Is this bug? I guess that it derives from the changes around flag
file done a while ago.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center