Function AlterTable

src/backend/commands/tablecmds.c:4802–4844

* AlterTable * Execute ALTER TABLE, which can be a list of subcommands * * ALTER TABLE is performed in three phases: * 1. Examine subcommands and perform pre-transformation checking. * 2. Validate and transform subcommands, and update system catalogs. * 3. Scan table(s) to check new constraints, and optionally recopy * the data into new table(s). * Phase 3 is not performed unless o

 * Some of the fields therein, such as the relid, are used here as well.
 */
void
AlterTable(AlterTableStmt *stmt, LOCKMODE lockmode,
		   AlterTableUtilityContext *context)
{
	Relation	rel;

	/* Caller is required to provide an adequate lock. */
	rel = relation_open(context->relid, NoLock);

	/*
	 * GPDB creates ALTER stmts and executes them internally as part of some
	 * partition related ALTER stmts, hence for such internal ALTER stmts
	 * can't meet this requirement.
	 */
	if (!stmt->is_internal)
		CheckTableNotInUse(rel, "ALTER TABLE");

	ATController(stmt, rel, stmt->cmds, stmt->relation->inh, lockmode, context);

	if (Gp_role == GP_ROLE_DISPATCH)
	{
		/*
		 * If a transaction is in progress, kill any idle QE backends. They
		 * might be running with obsolete information in their relcaches. Any
		 * relcache invalidation events sent by the ALTER TABLE subcommands
		 * won't be sent to the other backend until the end of transaction, and
		 * we don't have any better way of invalidating them. The primary
		 * writer backends should be up-to-date, because we have used that to
		 * execute all the subcommands, so they should've created local
		 * invalidation events for themselves.
		 */
		if (IsTransactionBlock())
			DisconnectAndDestroyUnusedQEs();

		if (stmt->cmds && ENABLE_DISPATCH())
			CdbDispatchUtilityStatement((Node *) stmt,
										DF_CANCEL_ON_ERROR |
										DF_WITH_SNAPSHOT |
										DF_NEED_TWO_PHASE,
										GetAssignedOidsForDispatch(),
										NULL);
	}
}

/* 
 * Populate the column encoding option for each column in the relation.