Re: Speed up JSON escape processing with SIMD plus other optimisations

[David Rowley]

On Thu, 23 May 2024 at 13:23, David Rowley <dgrowle...@gmail.com> wrote:
> Master:
> $ pgbench -n -f bench.sql -T 10 -M prepared postgres | grep tps
> tps = 362.494309 (without initial connection time)
> tps = 363.182458 (without initial connection time)
> tps = 362.679654 (without initial connection time)
>
> Master + 0001 + 0002
> $ pgbench -n -f bench.sql -T 10 -M prepared postgres | grep tps
> tps = 426.456885 (without initial connection time)
> tps = 430.573046 (without initial connection time)
> tps = 431.142917 (without initial connection time)
>
> About 18% faster.
>
> It would be much faster if we could also get rid of the
> escape_json_cstring() call in the switch default case of
> datum_to_json_internal(). row_to_json() would be heaps faster with
> that done. I considered adding a special case for the "text" type
> there, but in the end felt that we should just fix that with some
> hypothetical other patch that changes how output functions work.
> Others may feel it's worthwhile. I certainly could be convinced of it.

Just to turn that into performance numbers, I tried the attached
patch.  The numbers came out better than I thought.

Same test as before:

master + 0001 + 0002 + attached hacks:
$ pgbench -n -f bench.sql -T 10 -M prepared postgres | grep tps
tps = 616.094394 (without initial connection time)
tps = 615.928236 (without initial connection time)
tps = 614.175494 (without initial connection time)

About 70% faster than master.

David

diff --git a/src/backend/utils/adt/json.c b/src/backend/utils/adt/json.c
index a266f60ff3..b15f6c5e64 100644
--- a/src/backend/utils/adt/json.c
+++ b/src/backend/utils/adt/json.c
@@ -24,6 +24,7 @@
 #include "utils/builtins.h"
 #include "utils/date.h"
 #include "utils/datetime.h"
+#include "utils/fmgroids.h"
 #include "utils/json.h"
 #include "utils/jsonfuncs.h"
 #include "utils/lsyscache.h"
@@ -286,9 +287,15 @@ datum_to_json_internal(Datum val, bool is_null, StringInfo 
result,
                        pfree(jsontext);
                        break;
                default:
-                       outputstr = OidOutputFunctionCall(outfuncoid, val);
-                       escape_json_cstring(result, outputstr);
-                       pfree(outputstr);
+                       /* special case common case for text types */
+                       if (outfuncoid == F_TEXTOUT)
+                               escape_json_from_text(result, (text *) 
DatumGetPointer(val));
+                       else
+                       {
+                               outputstr = OidOutputFunctionCall(outfuncoid, 
val);
+                               escape_json_cstring(result, outputstr);
+                               pfree(outputstr);
+                       }
                        break;
        }
 }