[postgis-tickets] [PostGIS] #4368: Reorder struct layouts to minimize padding

[PostGIS]

#4368: Reorder struct layouts to minimize padding
--------------------------+---------------------------
  Reporter:  Algunenano   |      Owner:  Algunenano
      Type:  enhancement  |     Status:  assigned
  Priority:  medium       |  Milestone:  PostGIS 3.0.0
 Component:  postgis      |    Version:  trunk
Resolution:               |   Keywords:
--------------------------+---------------------------

Comment (by Algunenano):

 With Komzpa's idea, I decided to hack both ST_Subdivide and ST_Collect to
 print memory stats and test what was the impact using the bigpolygon
 table:

 {{{
 diff --git a/postgis/lwgeom_accum.c b/postgis/lwgeom_accum.c
 index db7ccd3fe..1d9c5844e 100644
 --- a/postgis/lwgeom_accum.c
 +++ b/postgis/lwgeom_accum.c
 @@ -240,6 +240,7 @@ pgis_geometry_collect_finalfn(PG_FUNCTION_ARGS)

      geometry_array = pgis_accum_finalfn(p, CurrentMemoryContext, fcinfo);
      result = PGISDirectFunctionCall1( LWGEOM_collect_garray,
 geometry_array );
 +    MemoryContextStats(CurrentMemoryContext);
      if (!result)
          PG_RETURN_NULL();

 diff --git a/postgis/lwgeom_dump.c b/postgis/lwgeom_dump.c
 index 133a2d7d0..92789c675 100644
 --- a/postgis/lwgeom_dump.c
 +++ b/postgis/lwgeom_dump.c
 @@ -400,6 +400,7 @@ Datum ST_Subdivide(PG_FUNCTION_ARGS)
      else
      {
          /* do when there is no more left */
 +        MemoryContextStats(funcctx->multi_call_memory_ctx);
          SRF_RETURN_DONE(funcctx);
      }
  }
 }}}


 SQL: `Select ST_Collect(geom) from ( select ST_Subdivide(geom) As geom
 FROM big_polygon ) _a;`


 * Before changes:

 ST_Subdivide:
 {{{
  multi-call context: 11795280 total in 1722 blocks; 3172560 free (9560
 chunks); 8622720 used
  total: 11795280 bytes in 1722 blocks; 3172560 free (9560 chunks); 8622720
 used
 }}}

 ST_Collect:
 {{{
  8069592 total in 11 blocks; 494824 free (2 chunks); 7574768 used
  total: 8069592 bytes in 11 blocks; 494824 free (2 chunks); 7574768 used
 }}}


 * After changes:

 Subdivide uses 2 blocks less (1710/1712). ~1% less total bytes used:
 {{{
  multi-call context: 11696976 total in 1710 blocks; 3134384 free (8883
 chunks); 8562592 used
  total: 11696976 bytes in 1710 blocks; 3134384 free (8883 chunks); 8562592
 used
 }}}

 ST_Collect uses 1 block less (10 vs 11). ~6.5% less total bytes used:
 {{{
  7545304 total in 10 blocks; 30032 free (2 chunks); 7515272 used
  total: 7545304 bytes in 10 blocks; 30032 free (2 chunks); 7515272 used
 }}}


 I don't see any measurable impact in performance in my machine

-- 
Ticket URL: <https://trac.osgeo.org/postgis/ticket/4368#comment:2>
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