Avoid unnecessary failure in SELECT concurrent with ALTER NO INHERIT.

If a query against an inheritance tree runs concurrently with an ALTER
TABLE that's disinheriting one of the tree members, it's possible to get
a "could not find inherited attribute" error because after obtaining lock
on the removed member, make_inh_translation_list sees that its columns
have attinhcount=0 and decides they aren't the columns it's looking for.

An ideal fix, perhaps, would avoid including such a just-removed member
table in the query at all; but there seems no way to accomplish that
without adding expensive catalog rechecks or creating a likelihood of
deadlocks.  Instead, let's just drop the check on attinhcount.  In this
way, a query that's included a just-disinherited child will still
succeed, which is not a completely unreasonable behavior.

This problem has existed for a long time, so back-patch to all supported
branches.  Also add an isolation test verifying related behaviors.

Patch by me; the new isolation test is based on Kyotaro Horiguchi's work.

Discussion: https://postgr.es/m/20170626.174612.23936762.horiguchi.kyotaro@lab.ntt.co.jp

diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index b441f7e5cacf07551650f3ad55ff8a91f150e710..266ee4db5e87c2ca3f26e8a31870733ba8bd8ae9 100644 (file)
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -1638,7 +1638,7 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
                 */
                if (old_attno < newnatts &&
                        (att = new_tupdesc->attrs[old_attno]) != NULL &&
-                       !att->attisdropped && att->attinhcount != 0 &&
+                       !att->attisdropped &&
                        strcmp(attname, NameStr(att->attname)) == 0)
                        new_attno = old_attno;
                else
@@ -1646,7 +1646,7 @@ make_inh_translation_list(Relation oldrelation, Relation newrelation,
                        for (new_attno = 0; new_attno < newnatts; new_attno++)
                        {
                                att = new_tupdesc->attrs[new_attno];
-                               if (!att->attisdropped && att->attinhcount != 0 &&
+                               if (!att->attisdropped &&
                                        strcmp(attname, NameStr(att->attname)) == 0)
                                        break;
                        }

diff --git a/src/test/isolation/expected/alter-table-4.out b/src/test/isolation/expected/alter-table-4.out
new file mode 100644 (file)
index 0000000..d2dac0b
--- /dev/null
+++ b/src/test/isolation/expected/alter-table-4.out
@@ -0,0 +1,57 @@
+Parsed test spec with 2 sessions
+
+starting permutation: s1b s1delc1 s2sel s1c s2sel
+step s1b: BEGIN;
+step s1delc1: ALTER TABLE c1 NO INHERIT p;
+step s2sel: SELECT SUM(a) FROM p; <waiting ...>
+step s1c: COMMIT;
+step s2sel: <... completed>
+sum            
+
+11             
+step s2sel: SELECT SUM(a) FROM p;
+sum            
+
+1              
+
+starting permutation: s1b s1delc1 s1addc2 s2sel s1c s2sel
+step s1b: BEGIN;
+step s1delc1: ALTER TABLE c1 NO INHERIT p;
+step s1addc2: ALTER TABLE c2 INHERIT p;
+step s2sel: SELECT SUM(a) FROM p; <waiting ...>
+step s1c: COMMIT;
+step s2sel: <... completed>
+sum            
+
+11             
+step s2sel: SELECT SUM(a) FROM p;
+sum            
+
+101            
+
+starting permutation: s1b s1dropc1 s2sel s1c s2sel
+step s1b: BEGIN;
+step s1dropc1: DROP TABLE c1;
+step s2sel: SELECT SUM(a) FROM p; <waiting ...>
+step s1c: COMMIT;
+step s2sel: <... completed>
+sum            
+
+1              
+step s2sel: SELECT SUM(a) FROM p;
+sum            
+
+1              
+
+starting permutation: s1b s1delc1 s1modc1a s2sel s1c s2sel
+step s1b: BEGIN;
+step s1delc1: ALTER TABLE c1 NO INHERIT p;
+step s1modc1a: ALTER TABLE c1 ALTER COLUMN a TYPE float;
+step s2sel: SELECT SUM(a) FROM p; <waiting ...>
+step s1c: COMMIT;
+step s2sel: <... completed>
+error in steps s1c s2sel: ERROR:  attribute "a" of relation "c1" does not match parent's type
+step s2sel: SELECT SUM(a) FROM p;
+sum            
+
+1              

diff --git a/src/test/isolation/isolation_schedule b/src/test/isolation/isolation_schedule
index 413cf028f164311fb495dc3cfae351d074a77885..254adaff42d470dcf9f64e495796b9a3c97e42be 100644 (file)
--- a/src/test/isolation/isolation_schedule
+++ b/src/test/isolation/isolation_schedule
@@ -56,6 +56,7 @@ test: multiple-cic
 test: alter-table-1
 test: alter-table-2
 test: alter-table-3
+test: alter-table-4
 test: create-trigger
 test: async-notify
 test: vacuum-reltuples

diff --git a/src/test/isolation/specs/alter-table-4.spec b/src/test/isolation/specs/alter-table-4.spec
new file mode 100644 (file)
index 0000000..a9c1a93
--- /dev/null
+++ b/src/test/isolation/specs/alter-table-4.spec
@@ -0,0 +1,37 @@
+# ALTER TABLE - Add and remove inheritance with concurrent reads
+
+setup
+{
+ CREATE TABLE p (a integer);
+ INSERT INTO p VALUES(1);
+ CREATE TABLE c1 () INHERITS (p);
+ INSERT INTO c1 VALUES(10);
+ CREATE TABLE c2 (a integer);
+ INSERT INTO c2 VALUES(100);
+}
+
+teardown
+{
+ DROP TABLE IF EXISTS c1, c2, p;
+}
+
+session "s1"
+step "s1b"     { BEGIN; }
+step "s1delc1" { ALTER TABLE c1 NO INHERIT p; }
+step "s1modc1a"        { ALTER TABLE c1 ALTER COLUMN a TYPE float; }
+step "s1addc2" { ALTER TABLE c2 INHERIT p; }
+step "s1dropc1"        { DROP TABLE c1; }
+step "s1c"     { COMMIT; }
+
+session "s2"
+step "s2sel"   { SELECT SUM(a) FROM p; }
+
+# NO INHERIT will not be visible to concurrent select,
+# since we identify children before locking them
+permutation "s1b" "s1delc1" "s2sel" "s1c" "s2sel"
+# adding inheritance likewise is not seen if s1 commits after s2 locks p
+permutation "s1b" "s1delc1" "s1addc2" "s2sel" "s1c" "s2sel"
+# but we do cope with DROP on a child table
+permutation "s1b" "s1dropc1" "s2sel" "s1c" "s2sel"
+# this case currently results in an error; doesn't seem worth preventing
+permutation "s1b" "s1delc1" "s1modc1a" "s2sel" "s1c" "s2sel"