Fix handling of NULLs when merging BRIN summaries

When merging BRIN summaries, union_tuples() did not correctly update the
target hasnulls/allnulls flags. When merging all-NULL summary into a
summary without any NULL values, the result had both flags set to false
(instead of having hasnulls=true).

This happened because the code only considered the hasnulls flags,
ignoring the possibility the source summary has allnulls=true.

Discovered while investigating issues with handling empty BRIN ranges
and handling of NULL values, but it's a separate problem (has nothing to
do with empty ranges).

Fixed by considering both flags on the source summary, and updating the
hasnulls flag on the target summary.

Backpatch to 11. The bug exists since 9.5 (where BRIN indexes were
introduced), but those releases are EOL already.

Discussion: https://postgr.es/m/9d993d0d-e431-2196-9ccc-0554d0e60154%40enterprisedb.com

diff --git a/src/backend/access/brin/brin_inclusion.c b/src/backend/access/brin/brin_inclusion.c
index 9d7cb36a47a003a97405ef806987329be05f21e7..75195ce23bd3779436018dd1c991033260de32da 100644 (file)
--- a/src/backend/access/brin/brin_inclusion.c
+++ b/src/backend/access/brin/brin_inclusion.c
@@ -515,10 +515,13 @@ brin_inclusion_union(PG_FUNCTION_ARGS)
        FmgrInfo   *finfo;
        Datum           result;
 
+       /* Does the "b" summary represent any NULL values? */
+       bool            b_has_nulls = (col_b->bv_hasnulls || col_b->bv_allnulls);
+
        Assert(col_a->bv_attno == col_b->bv_attno);
 
        /* Adjust "hasnulls". */
-       if (!col_a->bv_hasnulls && col_b->bv_hasnulls)
+       if (!col_a->bv_allnulls && b_has_nulls)
                col_a->bv_hasnulls = true;
 
        /* If there are no values in B, there's nothing left to do. */
@@ -533,10 +536,15 @@ brin_inclusion_union(PG_FUNCTION_ARGS)
         * B into A, and we're done.  We cannot run the operators in this case,
         * because values in A might contain garbage.  Note we already established
         * that B contains values.
+        *
+        * Also adjust "hasnulls" in order not to forget the summary represents NULL
+        * values. This is not redundant with the earlier update, because that only
+        * happens when allnulls=false.
         */
        if (col_a->bv_allnulls)
        {
                col_a->bv_allnulls = false;
+               col_a->bv_hasnulls = true;
                col_a->bv_values[INCLUSION_UNION] =
                        datumCopy(col_b->bv_values[INCLUSION_UNION],
                                          attr->attbyval, attr->attlen);

diff --git a/src/backend/access/brin/brin_minmax.c b/src/backend/access/brin/brin_minmax.c
index ad0d18ed39fc3d99191fd3f0be0c2b237a62182f..57c9294f269a3b0649d117143dea88e0f86059b3 100644 (file)
--- a/src/backend/access/brin/brin_minmax.c
+++ b/src/backend/access/brin/brin_minmax.c
@@ -249,10 +249,13 @@ brin_minmax_union(PG_FUNCTION_ARGS)
        FmgrInfo   *finfo;
        bool            needsadj;
 
+       /* Does the "b" summary represent any NULL values? */
+       bool            b_has_nulls = (col_b->bv_hasnulls || col_b->bv_allnulls);
+
        Assert(col_a->bv_attno == col_b->bv_attno);
 
        /* Adjust "hasnulls" */
-       if (!col_a->bv_hasnulls && col_b->bv_hasnulls)
+       if (!col_a->bv_allnulls && b_has_nulls)
                col_a->bv_hasnulls = true;
 
        /* If there are no values in B, there's nothing left to do */
@@ -267,10 +270,15 @@ brin_minmax_union(PG_FUNCTION_ARGS)
         * B into A, and we're done.  We cannot run the operators in this case,
         * because values in A might contain garbage.  Note we already established
         * that B contains values.
+        *
+        * Also adjust "hasnulls" in order not to forget the summary represents NULL
+        * values. This is not redundant with the earlier update, because that only
+        * happens when allnulls=false.
         */
        if (col_a->bv_allnulls)
        {
                col_a->bv_allnulls = false;
+               col_a->bv_hasnulls = true;
                col_a->bv_values[0] = datumCopy(col_b->bv_values[0],
                                                                                attr->attbyval, attr->attlen);
                col_a->bv_values[1] = datumCopy(col_b->bv_values[1],