From ca7841a24c27012e351d08dc36039233ae0d80e1 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Mon, 22 Jul 2019 11:09:06 -0400
Subject: [PATCH v2] Check partitions not in use

---
 src/backend/commands/tablecmds.c | 56 +++++++++++++++++++++++++-------
 1 file changed, 45 insertions(+), 11 deletions(-)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index f39f993e01..fd17aa4b5a 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -354,6 +354,7 @@ static void ATSimplePermissions(Relation rel, int allowed_targets);
 static void ATWrongRelkindError(Relation rel, int allowed_targets);
 static void ATSimpleRecursion(List **wqueue, Relation rel,
 							  AlterTableCmd *cmd, bool recurse, LOCKMODE lockmode);
+static void ATCheckPartitionsNotInUse(Relation rel, LOCKMODE lockmode);
 static void ATTypedTableRecursion(List **wqueue, Relation rel, AlterTableCmd *cmd,
 								  LOCKMODE lockmode);
 static List *find_typed_table_dependencies(Oid typeOid, const char *typeName,
@@ -3421,8 +3422,7 @@ CheckTableNotInUse(Relation rel, const char *stmt)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_IN_USE),
 		/* translator: first %s is a SQL command, eg ALTER TABLE */
-				 errmsg("cannot %s \"%s\" because "
-						"it is being used by active queries in this session",
+				 errmsg("cannot %s \"%s\" because it is being used by active queries in this session",
 						stmt, RelationGetRelationName(rel))));
 
 	if (rel->rd_rel->relkind != RELKIND_INDEX &&
@@ -3431,8 +3431,7 @@ CheckTableNotInUse(Relation rel, const char *stmt)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_IN_USE),
 		/* translator: first %s is a SQL command, eg ALTER TABLE */
-				 errmsg("cannot %s \"%s\" because "
-						"it has pending trigger events",
+				 errmsg("cannot %s \"%s\" because it has pending trigger events",
 						stmt, RelationGetRelationName(rel))));
 }
 
@@ -3910,16 +3909,19 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			break;
 		case AT_AddIdentity:
 			ATSimplePermissions(rel, ATT_TABLE | ATT_VIEW | ATT_FOREIGN_TABLE);
+			/* This command never recurses */
 			pass = AT_PASS_ADD_CONSTR;
 			break;
-		case AT_DropIdentity:
-			ATSimplePermissions(rel, ATT_TABLE | ATT_VIEW | ATT_FOREIGN_TABLE);
-			pass = AT_PASS_DROP;
-			break;
 		case AT_SetIdentity:
 			ATSimplePermissions(rel, ATT_TABLE | ATT_VIEW | ATT_FOREIGN_TABLE);
+			/* This command never recurses */
 			pass = AT_PASS_COL_ATTRS;
 			break;
+		case AT_DropIdentity:
+			ATSimplePermissions(rel, ATT_TABLE | ATT_VIEW | ATT_FOREIGN_TABLE);
+			/* This command never recurses */
+			pass = AT_PASS_DROP;
+			break;
 		case AT_DropNotNull:	/* ALTER COLUMN DROP NOT NULL */
 			ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
 			ATPrepDropNotNull(rel, recurse, recursing);
@@ -3985,7 +3987,8 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 			break;
 		case AT_DropConstraint: /* DROP CONSTRAINT */
 			ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
-			/* Recursion occurs during execution phase */
+			ATCheckPartitionsNotInUse(rel, lockmode);
+			/* Other recursion occurs during execution phase */
 			/* No command-specific prep needed except saving recurse flag */
 			if (recurse)
 				cmd->subtype = AT_DropConstraintRecurse;
@@ -5224,8 +5227,9 @@ ATSimpleRecursion(List **wqueue, Relation rel,
 				  AlterTableCmd *cmd, bool recurse, LOCKMODE lockmode)
 {
 	/*
-	 * Propagate to children if desired.  Only plain tables and foreign tables
-	 * have children, so no need to search for other relkinds.
+	 * Propagate to children if desired.  Only plain tables, foreign tables
+	 * and partitioned tables have children, so no need to search for other
+	 * relkinds.
 	 */
 	if (recurse &&
 		(rel->rd_rel->relkind == RELKIND_RELATION ||
@@ -5259,6 +5263,36 @@ ATSimpleRecursion(List **wqueue, Relation rel,
 	}
 }
 
+/*
+ * Obtain list of partitions of the given table, locking them all at the given
+ * lockmode and ensuring that they all pass CheckTableNotInUse.
+ *
+ * This function is a no-op if the given relation is not a partitioned table;
+ * in particular, nothing is done if it's a legacy inheritance parent.
+ */
+static void
+ATCheckPartitionsNotInUse(Relation rel, LOCKMODE lockmode)
+{
+	if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
+	{
+		List	   *inh;
+		ListCell   *cell;
+
+		inh = find_all_inheritors(RelationGetRelid(rel), lockmode, NULL);
+		/* first element is the parent rel; must ignore it */
+		for_each_cell(cell, inh, list_second_cell(inh))
+		{
+			Relation	childrel;
+
+			/* find_all_inheritors already got lock */
+			childrel = table_open(lfirst_oid(cell), NoLock);
+			CheckTableNotInUse(childrel, "ALTER TABLE");
+			table_close(childrel, NoLock);
+		}
+		list_free(inh);
+	}
+}
+
 /*
  * ATTypedTableRecursion
  *
-- 
2.17.1