Fix comparison of similarity to threshold in GIST trigram searches.

There was some very strange code here, dating to commit b525bf77, that
purported to work around an ancient gcc bug by forcing a float4 comparison
to be done as int instead.  Commit 5871b8848 broke that when it changed
one side of the comparison to "double" but left the comparison code alone.
Commit f576b17cd doubled down on the weirdness by introducing a "volatile"
marker, which had nothing to do with the actual problem.

Guess that the gcc bug, even if it's still present in the wild, was
triggered by comparison of float4's and can be avoided if we store the
result of cnt_sml() into a double before comparing to the double "nlimit".
This will at least work correctly on non-broken compilers, and it's way
more readable.

Per bug #14202 from Greg Navis.  Add a regression test based on his
example.

Report: <20160620115321[email protected]>

diff --git a/contrib/pg_trgm/expected/pg_trgm.out b/contrib/pg_trgm/expected/pg_trgm.out
index 78e8174f866a4d365fedd4589d90df3a83699c10..9bc55f1d0d33e4d40d7ebd7a6e6f909022bfa254 100644 (file)
--- a/contrib/pg_trgm/expected/pg_trgm.out
+++ b/contrib/pg_trgm/expected/pg_trgm.out
@@ -3838,3 +3838,56 @@ select * from test2 where t ~ '  z foo';
    z foo bar
 (1 row)
 
+-- Check similarity threshold (bug #14202)
+CREATE TEMP TABLE restaurants (city text);
+INSERT INTO restaurants SELECT 'Warsaw' FROM generate_series(1, 10000);
+INSERT INTO restaurants SELECT 'Szczecin' FROM generate_series(1, 10000);
+CREATE INDEX ON restaurants USING gist(city gist_trgm_ops);
+-- Similarity of the two names (for reference).
+SELECT similarity('Szczecin', 'Warsaw');
+ similarity 
+------------
+          0
+(1 row)
+
+-- Should get only 'Warsaw' for either setting of set_limit.
+EXPLAIN (COSTS OFF)
+SELECT DISTINCT city, similarity(city, 'Warsaw'), show_limit()
+  FROM restaurants WHERE city % 'Warsaw';
+                         QUERY PLAN                          
+-------------------------------------------------------------
+ Unique
+   ->  Sort
+         Sort Key: city, (similarity(city, 'Warsaw'::text))
+         ->  Bitmap Heap Scan on restaurants
+               Recheck Cond: (city % 'Warsaw'::text)
+               ->  Bitmap Index Scan on restaurants_city_idx
+                     Index Cond: (city % 'Warsaw'::text)
+(7 rows)
+
+SELECT set_limit(0.3);
+ set_limit 
+-----------
+       0.3
+(1 row)
+
+SELECT DISTINCT city, similarity(city, 'Warsaw'), show_limit()
+  FROM restaurants WHERE city % 'Warsaw';
+  city  | similarity | show_limit 
+--------+------------+------------
+ Warsaw |          1 |        0.3
+(1 row)
+
+SELECT set_limit(0.5);
+ set_limit 
+-----------
+       0.5
+(1 row)
+
+SELECT DISTINCT city, similarity(city, 'Warsaw'), show_limit()
+  FROM restaurants WHERE city % 'Warsaw';
+  city  | similarity | show_limit 
+--------+------------+------------
+ Warsaw |          1 |        0.5
+(1 row)
+

diff --git a/contrib/pg_trgm/sql/pg_trgm.sql b/contrib/pg_trgm/sql/pg_trgm.sql
index 6cefc8e643a6ebbb8a697682ea4caaf7dbf36cfb..244946bb8db558ca0a450d327f58731b381f5d0e 100644 (file)
--- a/contrib/pg_trgm/sql/pg_trgm.sql
+++ b/contrib/pg_trgm/sql/pg_trgm.sql
@@ -113,3 +113,24 @@ select * from test2 where t ~ 'z foo bar';
 select * from test2 where t ~ ' z foo bar';
 select * from test2 where t ~ '  z foo bar';
 select * from test2 where t ~ '  z foo';
+
+-- Check similarity threshold (bug #14202)
+
+CREATE TEMP TABLE restaurants (city text);
+INSERT INTO restaurants SELECT 'Warsaw' FROM generate_series(1, 10000);
+INSERT INTO restaurants SELECT 'Szczecin' FROM generate_series(1, 10000);
+CREATE INDEX ON restaurants USING gist(city gist_trgm_ops);
+
+-- Similarity of the two names (for reference).
+SELECT similarity('Szczecin', 'Warsaw');
+
+-- Should get only 'Warsaw' for either setting of set_limit.
+EXPLAIN (COSTS OFF)
+SELECT DISTINCT city, similarity(city, 'Warsaw'), show_limit()
+  FROM restaurants WHERE city % 'Warsaw';
+SELECT set_limit(0.3);
+SELECT DISTINCT city, similarity(city, 'Warsaw'), show_limit()
+  FROM restaurants WHERE city % 'Warsaw';
+SELECT set_limit(0.5);
+SELECT DISTINCT city, similarity(city, 'Warsaw'), show_limit()
+  FROM restaurants WHERE city % 'Warsaw';

diff --git a/contrib/pg_trgm/trgm_gist.c b/contrib/pg_trgm/trgm_gist.c
index 3a5aff9edee57f90bd45e462c39941dc772e0cc6..f52867df32407a771b9e62cd33ec64f2a32d68d2 100644 (file)
--- a/contrib/pg_trgm/trgm_gist.c
+++ b/contrib/pg_trgm/trgm_gist.c
@@ -296,16 +296,9 @@ gtrgm_consistent(PG_FUNCTION_ARGS)
 
            if (GIST_LEAF(entry))
            {                   /* all leafs contains orig trgm */
+               double      tmpsml = cnt_sml(qtrg, key, *recheck);
 
-               /*
-                * Prevent gcc optimizing the tmpsml variable using volatile
-                * keyword. Otherwise comparison of nlimit and tmpsml may give
-                * wrong results.
-                */
-               float4 volatile tmpsml = cnt_sml(qtrg, key, *recheck);
-
-               /* strange bug at freebsd 5.2.1 and gcc 3.3.3 */
-               res = (*(int *) &tmpsml == *(int *) &nlimit || tmpsml > nlimit);
+               res = (tmpsml >= nlimit);
            }
            else if (ISALLTRUE(key))
            {                   /* non-leaf contains signature */