I'm studying how the gist index works trying to improve the test coverage of
gistbuild.c.
Reading the source code I noticed that the gistInitBuffering function is not
covered, so I decided to start with it.
Reading the documentation and the source I understood that for this function to
be executed it is necessary to force
bufferring=on when creating the index or the index to be created is big enough
to not fit in the cache, am I correct?
Considering the above, I added two new index creation statements in the gist
regression test (patch attached) to create
an index using buffering=on and another to try to simulate an index that does
not fit in the cache.
With these new tests the coverage went from 45.3% to 85.5%, but I have some
doubts:
- Does this test make sense?
- Would there be a way to validate that the buffering was done correctly?
- Is this test necessary?
I've been studying Postgresql implementations and I'm just trying to start
contributing the source code.
--
Matheus Alcantara
diff --git a/src/test/regress/expected/gist.out b/src/test/regress/expected/gist.out
index a36b4c9c56..044986433a 100644
--- a/src/test/regress/expected/gist.out
+++ b/src/test/regress/expected/gist.out
@@ -46,6 +46,12 @@ vacuum analyze gist_tbl;
set enable_seqscan=off;
set enable_bitmapscan=off;
set enable_indexonlyscan=on;
+-- Build an index using buffering caused by a index build that don't fit on cache.
+set effective_cache_size = '1MB';
+create index gist_tbl_box_index_buffering on gist_tbl using gist (p, b, c);
+reset effective_cache_size;
+-- Force a index build using buffering.
+create index gist_tbl_box_index_forcing_buffering on gist_tbl using gist (p) with (buffering=on);
-- Test index-only scan with point opclass
create index gist_tbl_point_index on gist_tbl using gist (p);
-- check that the planner chooses an index-only scan
diff --git a/src/test/regress/sql/gist.sql b/src/test/regress/sql/gist.sql
index 3360266370..836ce84d71 100644
--- a/src/test/regress/sql/gist.sql
+++ b/src/test/regress/sql/gist.sql
@@ -55,6 +55,14 @@ set enable_seqscan=off;
set enable_bitmapscan=off;
set enable_indexonlyscan=on;
+-- Build an index using buffering caused by a index build that don't fit on cache.
+set effective_cache_size = '1MB';
+create index gist_tbl_box_index_buffering on gist_tbl using gist (p, b, c);
+reset effective_cache_size;
+
+-- Force an index build using buffering.
+create index gist_tbl_box_index_forcing_buffering on gist_tbl using gist (p) with (buffering=on);
+
-- Test index-only scan with point opclass
create index gist_tbl_point_index on gist_tbl using gist (p);
