Function AcquireRewriteLocks

src/backend/rewrite/rewriteHandler.c:141–346

* AcquireRewriteLocks - * Acquire suitable locks on all the relations mentioned in the Query. * These locks will ensure that the relation schemas don't change under us * while we are rewriting, planning, and executing the query. * * Caution: this may modify the querytree, therefore caller should usually * have done a copyObject() to make a writable copy of the querytree in the * curre

 * construction of a nested join was O(N^2) in the nesting depth.)
 */
void
AcquireRewriteLocks(Query *parsetree,
					bool forExecute,
					bool forUpdatePushedDown)
{
	ListCell      *l;
	int			   rt_index;
	acquireLocksOnSubLinks_context context;

	context.for_execute = forExecute;

	/*
	 * First, process RTEs of the current query level.
	 */
	rt_index = 0;
	foreach(l, parsetree->rtable)
	{
		RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
		Relation	rel;
		LOCKMODE	lockmode;
		bool        needLockUpgrade;
		List	   *newaliasvars;
		Index		curinputvarno;
		RangeTblEntry *curinputrte;
		ListCell   *ll;

		++rt_index;
		switch (rte->rtekind)
		{
			case RTE_RELATION:

				/*
				 * Grab the appropriate lock type for the relation, and do not
				 * release it until end of transaction.  This protects the
				 * rewriter, planner, and executor against schema changes
				 * mid-query.
				 *
				 * If forExecute is false, ignore rellockmode and just use
				 * AccessShareLock.
				 *
				 * CDB: The proper lock mode depends on whether the relation is
				 * local or distributed, which is discovered by heap_open().
				 * To handle this we make use of CdbOpenRelation().
				 * 
				 * For update should hold ExclusiveLock, see the discussion on
				 * https://groups.google.com/a/greenplum.org/d/msg/gpdb-dev/p-6_dNjnRMQ/OzTnb586AwAJ
				 *
				 * Update|DELETE may have to upgrade the locks to avoid global
				 * deadlock and CdbOpenRelation will do more check for AO table
				 * and GDD's status.
				 */
				needLockUpgrade = false;
				if (!forExecute)
					lockmode = AccessShareLock;
				else if (rt_index == parsetree->resultRelation)
				{
					lockmode = RowExclusiveLock;
					needLockUpgrade = (parsetree->commandType == CMD_UPDATE ||