diff options
Diffstat (limited to 'src/include/nodes/pathnodes.h')
| -rw-r--r-- | src/include/nodes/pathnodes.h | 53 |
1 files changed, 35 insertions, 18 deletions
diff --git a/src/include/nodes/pathnodes.h b/src/include/nodes/pathnodes.h index 5334a73b535..469c686e3fa 100644 --- a/src/include/nodes/pathnodes.h +++ b/src/include/nodes/pathnodes.h @@ -574,6 +574,24 @@ typedef struct PartitionSchemeData *PartitionScheme; * we know we will need it at least once (to price the sequential scan) * and may need it multiple times to price index scans. * + * A join relation is considered to be partitioned if it is formed from a + * join of two relations that are partitioned, have matching partitioning + * schemes, and are joined on an equijoin of the partitioning columns. + * Under those conditions we can consider the join relation to be partitioned + * by either relation's partitioning keys, though some care is needed if + * either relation can be forced to null by outer-joining. For example, an + * outer join like (A LEFT JOIN B ON A.a = B.b) may produce rows with B.b + * NULL. These rows may not fit the partitioning conditions imposed on B. + * Hence, strictly speaking, the join is not partitioned by B.b and thus + * partition keys of an outer join should include partition key expressions + * from the non-nullable side only. However, if a subsequent join uses + * strict comparison operators (and all commonly-used equijoin operators are + * strict), the presence of nulls doesn't cause a problem: such rows couldn't + * match anything on the other side and thus they don't create a need to do + * any cross-partition sub-joins. Hence we can treat such values as still + * partitioning the join output for the purpose of additional partitionwise + * joining, so long as a strict join operator is used by the next join. + * * If the relation is partitioned, these fields will be set: * * part_scheme - Partitioning scheme of the relation @@ -586,16 +604,15 @@ typedef struct PartitionSchemeData *PartitionScheme; * this relation that are partitioned tables * themselves, in hierarchical order * - * Note: A base relation always has only one set of partition keys, but a join - * relation may have as many sets of partition keys as the number of relations - * being joined. partexprs and nullable_partexprs are arrays containing - * part_scheme->partnatts elements each. Each of these elements is a list of - * partition key expressions. For a base relation each list in partexprs - * contains only one expression and nullable_partexprs is not populated. For a - * join relation, partexprs and nullable_partexprs contain partition key - * expressions from non-nullable and nullable relations resp. Lists at any - * given position in those arrays together contain as many elements as the - * number of joining relations. + * The partexprs and nullable_partexprs arrays each contain + * part_scheme->partnatts elements. Each of the elements is a list of + * partition key expressions. For partitioned base relations, there is one + * expression in each partexprs element, and nullable_partexprs is empty. + * For partitioned join relations, each base relation within the join + * contributes one partition key expression per partitioning column; + * that expression goes in the partexprs[i] list if the base relation + * is not nullable by this join or any lower outer join, or in the + * nullable_partexprs[i] list if the base relation is nullable. *---------- */ typedef enum RelOptKind @@ -716,16 +733,16 @@ typedef struct RelOptInfo Relids top_parent_relids; /* Relids of topmost parents (if "other" * rel) */ - /* used for partitioned relations */ - PartitionScheme part_scheme; /* Partitioning scheme. */ - int nparts; /* number of partitions */ + /* used for partitioned relations: */ + PartitionScheme part_scheme; /* Partitioning scheme */ + int nparts; /* Number of partitions */ struct PartitionBoundInfoData *boundinfo; /* Partition bounds */ - List *partition_qual; /* partition constraint */ + List *partition_qual; /* Partition constraint, if not the root */ struct RelOptInfo **part_rels; /* Array of RelOptInfos of partitions, - * stored in the same order of bounds */ - List **partexprs; /* Non-nullable partition key expressions. */ - List **nullable_partexprs; /* Nullable partition key expressions. */ - List *partitioned_child_rels; /* List of RT indexes. */ + * stored in the same order as bounds */ + List **partexprs; /* Non-nullable partition key expressions */ + List **nullable_partexprs; /* Nullable partition key expressions */ + List *partitioned_child_rels; /* List of RT indexes */ } RelOptInfo; /* |