Fix partition pruning with IS [NOT] NULL clauses

The original code was unable to prune partitions that could not possibly
contain NULL values, when the query specified less than all columns in a
multicolumn partition key.  Reorder the if-tests so that it is, and add
more commentary and regression tests.

Reported-by: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Co-authored-by: Dilip Kumar <dilipbalaut@gmail.com>
Co-authored-by: Amit Langote <Langote_Amit_f8@lab.ntt.co.jp>
Co-authored-by: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>
Reviewed-by: amul sul <sulamul@gmail.com>
Discussion: https://postgr.es/m/CAFjFpRc7qjLUfXLVBBC_HAnx644sjTYM=qVoT3TJ840HPbsTXw@mail.gmail.com

diff --git a/src/backend/partitioning/partprune.c b/src/backend/partitioning/partprune.c
index cdc61a89974b0acf7620d576065ba6b2c80d8886..354eb0d4e6055af35d1ddb9e0c8cc829a57a4391 100644 (file)
--- a/src/backend/partitioning/partprune.c
+++ b/src/backend/partitioning/partprune.c
@@ -853,54 +853,60 @@ gen_partprune_steps_internal(GeneratePruningStepsContext *context,
        }
    }
 
-   /*
-    * If generate_opsteps is set to false it means no OpExprs were directly
-    * present in the input list.
+   /*-----------
+    * Now generate some (more) pruning steps.  We have three strategies:
+    *
+    * 1) Generate pruning steps based on IS NULL clauses:
+    *   a) For list partitioning, null partition keys can only be found in
+    *      the designated null-accepting partition, so if there are IS NULL
+    *      clauses containing partition keys we should generate a pruning
+    *      step that gets rid of all partitions but that one.  We can
+    *      disregard any OpExpr we may have found.
+    *   b) For range partitioning, only the default partition can contain
+    *      NULL values, so the same rationale applies.
+    *   c) For hash partitioning, we only apply this strategy if we have
+    *      IS NULL clauses for all the keys.  Strategy 2 below will take
+    *      care of the case where some keys have OpExprs and others have
+    *      IS NULL clauses.
+    *
+    * 2) If not, generate steps based on OpExprs we have (if any).
+    *
+    * 3) If this doesn't work either, we may be able to generate steps to
+    *    prune just the null-accepting partition (if one exists), if we have
+    *    IS NOT NULL clauses for all partition keys.
     */
-   if (!generate_opsteps)
+   if (!bms_is_empty(nullkeys) &&
+       (part_scheme->strategy == PARTITION_STRATEGY_LIST ||
+        part_scheme->strategy == PARTITION_STRATEGY_RANGE ||
+        (part_scheme->strategy == PARTITION_STRATEGY_HASH &&
+         bms_num_members(nullkeys) == part_scheme->partnatts)))
    {
-       /*
-        * Generate one prune step for the information derived from IS NULL,
-        * if any.  To prune hash partitions, we must have found IS NULL
-        * clauses for all partition keys.
-        */
-       if (!bms_is_empty(nullkeys) &&
-           (part_scheme->strategy != PARTITION_STRATEGY_HASH ||
-            bms_num_members(nullkeys) == part_scheme->partnatts))
-       {
-           PartitionPruneStep *step;
-
-           step = gen_prune_step_op(context, InvalidStrategy,
-                                    false, NIL, NIL, nullkeys);
-           result = lappend(result, step);
-       }
-
-       /*
-        * Note that for IS NOT NULL clauses, simply having step suffices;
-        * there is no need to propagate the exact details of which keys are
-        * required to be NOT NULL.  Hash partitioning expects to see actual
-        * values to perform any pruning.
-        */
-       if (!bms_is_empty(notnullkeys) &&
-           part_scheme->strategy != PARTITION_STRATEGY_HASH)
-       {
-           PartitionPruneStep *step;
+       PartitionPruneStep *step;
 
-           step = gen_prune_step_op(context, InvalidStrategy,
-                                    false, NIL, NIL, NULL);
-           result = lappend(result, step);
-       }
+       /* Strategy 1 */
+       step = gen_prune_step_op(context, InvalidStrategy,
+                                false, NIL, NIL, nullkeys);
+       result = lappend(result, step);
    }
-   else
+   else if (generate_opsteps)
    {
        PartitionPruneStep *step;
 
-       /* Generate pruning steps from OpExpr clauses in keyclauses. */
+       /* Strategy 2 */
        step = gen_prune_steps_from_opexps(part_scheme, context,
                                           keyclauses, nullkeys);
        if (step != NULL)
            result = lappend(result, step);
    }
+   else if (bms_num_members(notnullkeys) == part_scheme->partnatts)
+   {
+       PartitionPruneStep *step;
+
+       /* Strategy 3 */
+       step = gen_prune_step_op(context, InvalidStrategy,
+                                false, NIL, NIL, NULL);
+       result = lappend(result, step);
+   }
 
    /*
     * Finally, results from all entries appearing in result should be

diff --git a/src/test/regress/expected/partition_prune.out b/src/test/regress/expected/partition_prune.out
index d15f1d37f131bc3b87e783eeb84d957a704a8910..022b7c55c7da9af56e69b591839de7e017acf0c8 100644 (file)
--- a/src/test/regress/expected/partition_prune.out
+++ b/src/test/regress/expected/partition_prune.out
@@ -993,6 +993,47 @@ explain (costs off) select * from mc2p where a = 1 and b > 1;
          Filter: ((b > 1) AND (a = 1))
 (3 rows)
 
+-- all partitions but the default one should be pruned
+explain (costs off) select * from mc2p where a = 1 and b is null;
+                QUERY PLAN                 
+-------------------------------------------
+ Append
+   ->  Seq Scan on mc2p_default
+         Filter: ((b IS NULL) AND (a = 1))
+(3 rows)
+
+explain (costs off) select * from mc2p where a is null and b is null;
+                  QUERY PLAN                   
+-----------------------------------------------
+ Append
+   ->  Seq Scan on mc2p_default
+         Filter: ((a IS NULL) AND (b IS NULL))
+(3 rows)
+
+explain (costs off) select * from mc2p where a is null and b = 1;
+                QUERY PLAN                 
+-------------------------------------------
+ Append
+   ->  Seq Scan on mc2p_default
+         Filter: ((a IS NULL) AND (b = 1))
+(3 rows)
+
+explain (costs off) select * from mc2p where a is null;
+           QUERY PLAN           
+--------------------------------
+ Append
+   ->  Seq Scan on mc2p_default
+         Filter: (a IS NULL)
+(3 rows)
+
+explain (costs off) select * from mc2p where b is null;
+           QUERY PLAN           
+--------------------------------
+ Append
+   ->  Seq Scan on mc2p_default
+         Filter: (b IS NULL)
+(3 rows)
+
 -- boolean partitioning
 create table boolpart (a bool) partition by list (a);
 create table boolpart_default partition of boolpart default;

diff --git a/src/test/regress/sql/partition_prune.sql b/src/test/regress/sql/partition_prune.sql
index b8e823d5620efb616f2546d6d30d1d5c563cfde8..2357f02cde9395730d7f6ca3d568c7a942490664 100644 (file)
--- a/src/test/regress/sql/partition_prune.sql
+++ b/src/test/regress/sql/partition_prune.sql
@@ -137,6 +137,13 @@ explain (costs off) select * from mc2p where a = 2 and b < 1;
 explain (costs off) select * from mc2p where a > 1;
 explain (costs off) select * from mc2p where a = 1 and b > 1;
 
+-- all partitions but the default one should be pruned
+explain (costs off) select * from mc2p where a = 1 and b is null;
+explain (costs off) select * from mc2p where a is null and b is null;
+explain (costs off) select * from mc2p where a is null and b = 1;
+explain (costs off) select * from mc2p where a is null;
+explain (costs off) select * from mc2p where b is null;
+
 -- boolean partitioning
 create table boolpart (a bool) partition by list (a);
 create table boolpart_default partition of boolpart default;