Prevent infinite insertion loops in spgdoinsert().

Formerly we just relied on operator classes that assert longValuesOK
to eventually shorten the leaf value enough to fit on an index page.
That fails since the introduction of INCLUDE-column support (commit
09c1c6ab4), because the INCLUDE columns might alone take up more
than a page, meaning no amount of leaf-datum compaction will get
the job done.  At least with spgtextproc.c, that leads to an infinite
loop, since spgtextproc.c won't throw an error for not being able
to shorten the leaf datum anymore.

To fix without breaking cases that would otherwise work, add logic
to spgdoinsert() to verify that the leaf tuple size is decreasing
after each "choose" step.  Some opclasses might not decrease the
size on every single cycle, and in any case, alignment roundoff
of the tuple size could obscure small gains.  Therefore, allow
up to 10 cycles without additional savings before throwing an
error.  (Perhaps this number will need adjustment, but it seems
quite generous right now.)

As long as we've developed this logic, let's back-patch it.
The back branches don't have INCLUDE columns to worry about, but
this seems like a good defense against possible bugs in operator
classes.  We already know that an infinite loop here is pretty
unpleasant, so having a defense seems to outweigh the risk of
breaking things.  (Note that spgtextproc.c is actually the only
known opclass with longValuesOK support, so that this is all moot
for known non-core opclasses anyway.)

Per report from Dilip Kumar.

Discussion: https://postgr.es/m/CAFiTN-uxP_soPhVG840tRMQTBmtA_f_Y8N51G7DKYYqDh7XN-A@mail.gmail.com

1 files changed, 10 insertions, 0 deletions

diff --git a/src/test/modules/spgist_name_ops/sql/spgist_name_ops.sql b/src/test/modules/spgist_name_ops/sql/spgist_name_ops.sql
index 76e78ba41c7..982f221a8b2 100644
--- a/src/test/modules/spgist_name_ops/sql/spgist_name_ops.sql
+++ b/src/test/modules/spgist_name_ops/sql/spgist_name_ops.sql
@@ -27,6 +27,12 @@ select * from t
   where f1 > 'binary_upgrade_set_n' and f1 < 'binary_upgrade_set_p'
   order by 1;
 
+-- Verify clean failure when INCLUDE'd columns result in overlength tuple
+-- The error message details are platform-dependent, so show only SQLSTATE
+\set VERBOSITY sqlstate
+insert into t values(repeat('xyzzy', 12), 42, repeat('xyzzy', 4000));
+\set VERBOSITY default
+
 drop index t_f1_f2_f3_idx;
 
 create index on t using spgist(f1 name_ops_old) include(f2, f3);
@@ -39,3 +45,7 @@ select * from t
 select * from t
   where f1 > 'binary_upgrade_set_n' and f1 < 'binary_upgrade_set_p'
   order by 1;
+
+\set VERBOSITY sqlstate
+insert into t values(repeat('xyzzy', 12), 42, repeat('xyzzy', 4000));
+\set VERBOSITY default