Smart group cache-build fails for extremely large groups

The smart group cache-build mechanism (CRM_Contact_BAO_GroupContactCache::load) produces an out-of-memory error when processing large smart-groups. Specifically, it includes this:

--------
$dao = CRM_Core_DAO::executeQuery( $sql );

$values = array( );
while ( $dao->fetch( ) ) {
$values[] = "({$groupID},{$dao->$idName})";
}

$groupIDs = array( $groupID );
self::remove( $groupIDs );
self::store ( $groupIDs, $values );
--------

The snippet loads the full group membership into memory before writing it out – which leads to the out-of-memory exception. Recommended steps:

• Write some unit-tests for smart groups
• Update GroupContactCache to use "INSERT INTO ... SELECT ..."