Refactor code controlling constraint creation evaluation

The code refactored in this commit is present in XC since the beginning of
the project and was outdated. The former code was put inside the utility
deparser to control UNIQUE, PRIMARY KEY, EXCLUDE and FOREIGN KEY creation.
This was a fundamental mistake as this did not allow control of FOREIGN KEY
creation with generic functions that could also be used to evaluate the
shippability of constraints when issuing a DML on a given relation or when
modifying a relation distribution with ALTER TABLE (online data redistribution
feature).
Now all this control is put directly inside Postgres-XC shippability evaluation
code and can be used in a wider way than the previous implementation. All the
error messages are now made generic and refer to the impossibility to create
constraints whose evaluation cannot be enforced to remote nodes.
Postgres-XC does not support yet global constraints, but once it does, it will
be necessary to remove the error messages referring to constraint evaluation
and to use the APIs implemented in this commit not to control the creation of
constraints but to check the shippability of a Query for a given relation
constraint.
The old code was also deeply lacking evaluation of index expressions, so some
control is added about that. A regression test called xc_constraints check the
shippability of constraints created on tables depending on their distribution.
Documentation is also updated, but might need more completion.
The code in this commit checks if redistribution with ALTER TABLE can be done
according to the given constraints already on it for UNIQUE, EXCLUDE and PRIMARY
KEY. For example, you should not be able to change a replicated table with a
primary key to roundrobin you cannot ensure the uniqueness of a key on such
tables so now this is protected properly. However, such checks are still missing
for FOREIGN KEY and REFERENCES.

1 files changed, 3 insertions, 214 deletions

diff --git a/src/backend/parser/parse_utilcmd.c b/src/backend/parser/parse_utilcmd.c
index 27e0a86e4b..9fd4a09fe4 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -53,6 +53,7 @@
 #include "parser/parse_type.h"
 #include "parser/parse_utilcmd.h"
 #ifdef PGXC
+#include "optimizer/pgxcship.h"
 #include "pgxc/locator.h"
 #include "pgxc/pgxc.h"
 #include "optimizer/pgxcplan.h"
@@ -133,9 +134,6 @@ static void transformConstraintAttrs(CreateStmtContext *cxt,
 						 List *constraintList);
 static void transformColumnType(CreateStmtContext *cxt, ColumnDef *column);
 static void setSchemaName(char *context_schema, char **stmt_schema_name);
-#ifdef PGXC
-static void checkLocalFKConstraints(CreateStmtContext *cxt);
-#endif
 
 /*
  * transformCreateStmt -
@@ -1475,9 +1473,6 @@ static IndexStmt *
 transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 {
 	IndexStmt  *index;
-#ifdef PGXC
-		bool		isLocalSafe = false;
-#endif
 	ListCell   *lc;
 
 	index = makeNode(IndexStmt);
@@ -1740,22 +1735,6 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 			if (strcmp(column->colname, key) == 0)
 			{
 				found = true;
-
-#ifdef PGXC
-				/*
-			 	 * Only allow locally enforceable constraints.
-				 * See if it is a distribution column
-				 * If not set, set it to first column in index.
-				 * If primary key, we prefer that over a unique constraint.
-				 */
-			   if (IS_PGXC_COORDINATOR && !isLocalSafe)
-			   {
-					if (cxt->distributeby)
-						isLocalSafe = CheckLocalIndexColumn (
-								ConvertToLocatorType(cxt->distributeby->disttype),
-								cxt->distributeby->colname, key);
-			   }
-#endif
 				break;
 			}
 		}
@@ -1859,16 +1838,9 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 			 * If not set, set it to first column in index.
 			 * If primary key, we prefer that over a unique constraint.
 			 */
-			if (index->indexParams == NIL
-					&& (index->primary || !cxt->fallback_dist_col))
-			{
+			if (index->indexParams == NIL &&
+				(index->primary || !cxt->fallback_dist_col))
 				cxt->fallback_dist_col = pstrdup(key);
-			}
-
-			/* Existing table, check if it is safe */
-			if (cxt->isalter && !cxt->distributeby && !isLocalSafe)
-				isLocalSafe = CheckLocalIndexColumn (
-						cxt->rel->rd_locator_info->locatorType, cxt->rel->rd_locator_info->partAttrName, key);
 		}
 #endif
 
@@ -1883,15 +1855,6 @@ transformIndexConstraint(Constraint *constraint, CreateStmtContext *cxt)
 		iparam->nulls_ordering = SORTBY_NULLS_DEFAULT;
 		index->indexParams = lappend(index->indexParams, iparam);
 	}
-#ifdef PGXC
-		if (IS_PGXC_COORDINATOR && cxt->distributeby
-				&& (cxt->distributeby->disttype == DISTTYPE_HASH ||
-					cxt->distributeby->disttype == DISTTYPE_MODULO)
-				&& !isLocalSafe)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
-					errmsg("Unique index of partitioned table must contain the hash distribution column.")));
-#endif
 
 	return index;
 }
@@ -1945,12 +1908,6 @@ transformFKConstraints(CreateStmtContext *cxt,
 		}
 	}
 
-#ifdef PGXC
-	/* Only allow constraints that are locally enforceable - no distributed ones */
-	if (IS_PGXC_COORDINATOR)
-		checkLocalFKConstraints(cxt);
-#endif
-
 	/*
 	 * For CREATE TABLE or ALTER TABLE ADD COLUMN, gin up an ALTER TABLE ADD
 	 * CONSTRAINT command to execute after the basic command is complete. (If
@@ -2906,171 +2863,3 @@ setSchemaName(char *context_schema, char **stmt_schema_name)
 						"different from the one being created (%s)",
 						*stmt_schema_name, context_schema)));
 }
-
-#ifdef PGXC
-/*
- * CheckLocalIndexColumn
- *
- * Checks whether or not the index can be safely enforced locally
- */
-bool
-CheckLocalIndexColumn (char loctype, char *partcolname, char *indexcolname)
-{
-
-	if (loctype == LOCATOR_TYPE_REPLICATED)
-		/* always safe */
-		return true;
-	if (loctype == LOCATOR_TYPE_RROBIN)
-			ereport(ERROR,
-					(errcode(ERRCODE_INVALID_COLUMN_REFERENCE),
-					errmsg("Cannot locally enforce a unique index on round robin distributed table.")));
-	else if (loctype == LOCATOR_TYPE_HASH || loctype == LOCATOR_TYPE_MODULO)
-	{
-		if (partcolname && indexcolname && strcmp(partcolname, indexcolname) == 0)
-			return true;
-	}
-	return false;
-}
-
-
-/*
- * check to see if the constraint can be enforced locally
- * if not, an error will be thrown
- */
-static void
-checkLocalFKConstraints(CreateStmtContext *cxt)
-{
-	ListCell *fkclist;
-
-	foreach(fkclist, cxt->fkconstraints)
-	{
-		Constraint *constraint;
-		Oid pk_rel_id;
-		char refloctype;
-		char *checkcolname = NULL;
-
-		constraint = (Constraint *) lfirst(fkclist);
-
-		/*
-		 * If constraint references to the table itself, it is safe
-		 * Check if relation name is the same
-		 */
-		if (constraint->pktable &&
-			strcmp(constraint->pktable->relname,cxt->relation->relname) == 0)
-		{
-			/* Is namespace also the same ? */
-			char *fkcon_schemaname = NULL;
-
-			if (!cxt->relation->schemaname &&
-				!constraint->pktable->schemaname)
-				continue;
-
-			if (!constraint->pktable->schemaname)
-			{
-				/* Schema name is not defined, look for current one */
-				List   *search_path = fetch_search_path(false);
-				fkcon_schemaname = get_namespace_name(linitial_oid(search_path));
-				list_free(search_path);
-			}
-			else
-				fkcon_schemaname = constraint->pktable->schemaname;
-
-			/*
-			 * If schema name and relation name are the same, table
-			 * references to itself, so constraint is safe
-			 */
-			if (fkcon_schemaname &&
-				strcmp(fkcon_schemaname,
-					   cxt->relation->schemaname) == 0)
-				continue;
-		}
-
-		pk_rel_id = RangeVarGetRelid(constraint->pktable, NoLock, false);
-
-		refloctype = GetLocatorType(pk_rel_id);
-
-		/* If referenced table is replicated, the constraint is safe */
-		if (refloctype == LOCATOR_TYPE_REPLICATED)
-			continue;
-		else if (refloctype == LOCATOR_TYPE_RROBIN)
-		{
-			ereport(ERROR,
-					(errcode(ERRCODE_SYNTAX_ERROR),
-					errmsg("Cannot reference a round robin table in a foreign key constraint")));
-		}
-
-		/*
-		 * See if we are hash or modulo partitioned and the column appears in the
-		 * constraint, and it corresponds to the position in the referenced table.
-		 */
-		if (cxt->isalter)
-		{
-			if (cxt->rel->rd_locator_info->locatorType == LOCATOR_TYPE_HASH ||
-				cxt->rel->rd_locator_info->locatorType == LOCATOR_TYPE_MODULO)
-			{
-				checkcolname = cxt->rel->rd_locator_info->partAttrName;
-			}
-		}
-		else
-		{
-			if (cxt->distributeby)
-			{
-				if (cxt->distributeby->disttype == DISTTYPE_HASH ||
-					cxt->distributeby->disttype == DISTTYPE_MODULO)
-					checkcolname = cxt->distributeby->colname;
-			}
-			else
-			{
-				if (cxt->fallback_dist_col)
-					checkcolname = cxt->fallback_dist_col;
-			}
-		}
-
-		if (checkcolname)
-		{
-			int pos = 0;
-
-			ListCell *attritem;
-
-			foreach(attritem, constraint->fk_attrs)
-			{
-				char *attrname = (char *) strVal(lfirst(attritem));
-
-				if (strcmp(checkcolname, attrname) == 0)
-				{
-					/* Found the ordinal position in constraint */
-					break;
-				}
-				pos++;
-			}
-
-			if (pos >= list_length(constraint->fk_attrs))
-				ereport(ERROR,
-						(errcode(ERRCODE_SYNTAX_ERROR),
-						 errmsg("Hash/Modulo distributed table must include distribution column in index")));
-
-			/*
-			 * The check to make sure that the referenced column in pk table is the same
-			 * as the one used to distribute it makes sense only when the user
-			 * supplies the name of the referenced colum while adding the constraint
-			 * because if the user did not specify it the system will choose the pk column
-			 * which will obviously be the one used to distribute it knowing the
-			 * existing constraints in XC
-			 * This is required to make sure that both
-			 * alter table dtab add foreign key (b) references rtab(a);
-			 * and
-			 * alter table dtab add foreign key (b) references rtab;
-			 * behave similarly
-			 */
-			if (constraint->pk_attrs != NULL)
-			{
-				/* Verify that the referenced table is partitioned at the same position in the index */
-				if (!IsDistColumnForRelId(pk_rel_id, strVal(list_nth(constraint->pk_attrs,pos))))
-					ereport(ERROR,
-							(errcode(ERRCODE_SYNTAX_ERROR),
-							errmsg("Hash/Modulo distribution column does not refer to hash/modulo distribution column in referenced table.")));
-			}
-		}
-	}
-}
-#endif