Re: Is it useful to record whether plans are generic or custom? - Mailing list pgsql-hackers

At Thu, 21 May 2020 12:18:16 +0900, Fujii Masao <masao.fujii@oss.nttdata.com> wrote in
>
>
> On 2020/05/20 21:56, Atsushi Torikoshi wrote:
> > On Wed, May 20, 2020 at 1:32 PM Kyotaro Horiguchi
> > <horikyota.ntt@gmail.com <mailto:horikyota.ntt@gmail.com>> wrote:
> >     At Tue, 19 May 2020 22:56:17 +0900, Atsushi Torikoshi
> >     <atorik@gmail.com <mailto:atorik@gmail.com>> wrote in
> >      > On Sat, May 16, 2020 at 6:01 PM legrand legrand
> >      > <legrand_legrand@hotmail.com <mailto:legrand_legrand@hotmail.com>>
> >      > wrote:
> >      >
> >      > BTW, I'd also appreciate other opinions about recording the number
> >      > of generic and custom plans on pg_stat_statemtents.
> >     If you/we just want to know how a prepared statement is executed,
> >     couldn't we show that information in pg_prepared_statements view?
> >     =# select * from pg_prepared_statements;
> >     -[ RECORD 1 ]---+----------------------------------------------------
> >     name            | stmt1
> >     statement       | prepare stmt1 as select * from t where b = $1;
> >     prepare_time    | 2020-05-20 12:01:55.733469+09
> >     parameter_types | {text}
> >     from_sql        | t
> >     exec_custom     | 5    <- existing num_custom_plans
> >     exec_total          | 40   <- new member of CachedPlanSource
> > Thanks, Horiguchi-san!
> > Adding counters to pg_prepared_statements seems useful when we want
> > to know the way prepared statements executed in the current session.
>
> I like the idea exposing more CachedPlanSource fields in
> pg_prepared_statements. I agree it's useful, e.g., for the debug
> purpose.
> This is why I implemented the similar feature in my extension.
> Please see [1] for details.

Thanks. I'm not sure plan_cache_mode should be a part of the view.
Cost numbers would look better if it is cooked a bit.  Is it worth
being in core?

=# select * from pg_prepared_statements;
-[ RECORD 1 ]---+--------------------------------------------
name            | p1
statement       | prepare p1 as select a from t where a = $1;
prepare_time    | 2020-05-21 15:41:50.419578+09
parameter_types | {integer}
from_sql        | t
calls           | 7
custom_calls    | 5
plan_generation | 6
generic_cost    | 4.3100000000000005
custom_cost     | 9.31

Perhaps plan_generation is not needed there.

> > And I also feel adding counters to pg_stat_statements will be
> > convenient
> > especially in production environments because it enables us to get
> > information about not only the current session but all sessions of a
> > PostgreSQL instance.
>
> +1

Agreed. It is global and persistent.

At Tue, 19 May 2020 22:56:17 +0900, Atsushi Torikoshi <atorik@gmail.com> wrote in
> Instead, I'm now considering using a static hash for prepared queries
> (static HTAB *prepared_queries).

That might be complex and fragile considering nested query and SPI
calls.  I'm not sure, but could we use ActivePortal?
ActivePortal->cplan is a CachedPlan, which can hold the generic/custom
information.

Instead,


> [1]
> https://github.com/MasaoFujii/pg_cheat_funcs#record-pg_cached_plan_sourcestmt-text

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center
From 1c6a3dd41a59504244134ee44ddd4516191656da Mon Sep 17 00:00:00 2001
From: Kyotaro Horiguchi <horikyoga.ntt@gmail.com>
Date: Thu, 21 May 2020 15:32:38 +0900
Subject: [PATCH] Expose counters of plancache to pg_prepared_statements

We didn't have an easy way to find how many times generic or custom
plans of a prepared statement have been executed.  This patch exposes
such numbers and costs of both plans in pg_prepared_statements.
---
 doc/src/sgml/catalogs.sgml            | 45 +++++++++++++++++++++++++++
 src/backend/commands/prepare.c        | 30 ++++++++++++++++--
 src/backend/utils/cache/plancache.c   | 13 ++++----
 src/include/catalog/pg_proc.dat       |  6 ++--
 src/include/utils/plancache.h         |  5 +--
 src/test/regress/expected/prepare.out | 43 +++++++++++++++++++++++++
 src/test/regress/expected/rules.out   |  9 ++++--
 src/test/regress/sql/prepare.sql      |  9 ++++++
 8 files changed, 144 insertions(+), 16 deletions(-)

diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml
index b1b077c97f..950ed30694 100644
--- a/doc/src/sgml/catalogs.sgml
+++ b/doc/src/sgml/catalogs.sgml
@@ -10826,6 +10826,51 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
        frontend/backend protocol
       </para></entry>
      </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>calls</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of times the prepared statement was executed
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>custom_calls</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of times generic plan is executed for the prepared statement
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>plan_geneation</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of times execution plan was generated for the prepared statement
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>generic_cost</structfield> <type>double precision</type>
+      </para>
+      <para>
+       Estimated cost of generic plan. NULL if not yet planned.
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+       <structfield>custom_cost</structfield> <type>double precision</type>
+      </para>
+      <para>
+       Estimated cost of custom plans. NULL if not yet planned. This is mean of the estimated costs for the past calls
includingplanning cost.
 
+      </para></entry>
+     </row>
     </tbody>
    </tgroup>
   </table>
diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 80d6df8ac1..e6755df543 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -723,7 +723,7 @@ pg_prepared_statement(PG_FUNCTION_ARGS)
      * build tupdesc for result tuples. This must match the definition of the
      * pg_prepared_statements view in system_views.sql
      */
-    tupdesc = CreateTemplateTupleDesc(5);
+    tupdesc = CreateTemplateTupleDesc(10);
     TupleDescInitEntry(tupdesc, (AttrNumber) 1, "name",
                        TEXTOID, -1, 0);
     TupleDescInitEntry(tupdesc, (AttrNumber) 2, "statement",
@@ -734,6 +734,16 @@ pg_prepared_statement(PG_FUNCTION_ARGS)
                        REGTYPEARRAYOID, -1, 0);
     TupleDescInitEntry(tupdesc, (AttrNumber) 5, "from_sql",
                        BOOLOID, -1, 0);
+    TupleDescInitEntry(tupdesc, (AttrNumber) 6, "calls",
+                       INT8OID, -1, 0);
+    TupleDescInitEntry(tupdesc, (AttrNumber) 7, "custom_calls",
+                       INT8OID, -1, 0);
+    TupleDescInitEntry(tupdesc, (AttrNumber) 8, "plan_generation",
+                       INT8OID, -1, 0);
+    TupleDescInitEntry(tupdesc, (AttrNumber) 9, "generic_cost",
+                       FLOAT8OID, -1, 0);
+    TupleDescInitEntry(tupdesc, (AttrNumber) 10, "custom_cost",
+                       FLOAT8OID, -1, 0);
 
     /*
      * We put all the tuples into a tuplestore in one scan of the hashtable.
@@ -755,8 +765,8 @@ pg_prepared_statement(PG_FUNCTION_ARGS)
         hash_seq_init(&hash_seq, prepared_queries);
         while ((prep_stmt = hash_seq_search(&hash_seq)) != NULL)
         {
-            Datum        values[5];
-            bool        nulls[5];
+            Datum        values[10];
+            bool        nulls[10];
 
             MemSet(nulls, 0, sizeof(nulls));
 
@@ -766,6 +776,20 @@ pg_prepared_statement(PG_FUNCTION_ARGS)
             values[3] = build_regtype_array(prep_stmt->plansource->param_types,
                                             prep_stmt->plansource->num_params);
             values[4] = BoolGetDatum(prep_stmt->from_sql);
+            values[5] = Int64GetDatumFast(prep_stmt->plansource->num_total_calls);
+            values[6] = Int64GetDatumFast(prep_stmt->plansource->num_custom_plans);
+            values[7] = Int64GetDatumFast(prep_stmt->plansource->generation);
+            if (prep_stmt->plansource->generic_cost >= 0.0)
+                values[8] = Float8GetDatum(prep_stmt->plansource->generic_cost);
+            else
+                nulls[8] = true;
+
+            if (prep_stmt->plansource->num_custom_plans > 0)
+                values[9] =
+                    Float8GetDatum(prep_stmt->plansource->total_custom_cost /
+                                   prep_stmt->plansource->num_custom_plans);
+            else
+                nulls[9] = true;
 
             tuplestore_putvalues(tupstore, tupdesc, values, nulls);
         }
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
index 75b475c179..d91444f60f 100644
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -286,6 +286,7 @@ CreateOneShotCachedPlan(RawStmt *raw_parse_tree,
     plansource->generic_cost = -1;
     plansource->total_custom_cost = 0;
     plansource->num_custom_plans = 0;
+    plansource->num_total_calls = 0;
 
     return plansource;
 }
@@ -1213,14 +1214,13 @@ GetCachedPlan(CachedPlanSource *plansource, ParamListInfo boundParams,
     {
         /* Build a custom plan */
         plan = BuildCachedPlan(plansource, qlist, boundParams, queryEnv);
-        /* Accumulate total costs of custom plans, but 'ware overflow */
-        if (plansource->num_custom_plans < INT_MAX)
-        {
-            plansource->total_custom_cost += cached_plan_cost(plan, true);
-            plansource->num_custom_plans++;
-        }
+        /* Accumulate total costs of custom plans */
+        plansource->total_custom_cost += cached_plan_cost(plan, true);
+        plansource->num_custom_plans++;
     }
 
+    plansource->num_total_calls++;
+
     Assert(plan != NULL);
 
     /* Flag the plan as in use by caller */
@@ -1575,6 +1575,7 @@ CopyCachedPlan(CachedPlanSource *plansource)
     newsource->generic_cost = plansource->generic_cost;
     newsource->total_custom_cost = plansource->total_custom_cost;
     newsource->num_custom_plans = plansource->num_custom_plans;
+    newsource->num_total_calls = plansource->num_total_calls;
 
     MemoryContextSwitchTo(oldcxt);
 
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 61f2c2f5b4..48d0d88d97 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7743,9 +7743,9 @@
 { oid => '2510', descr => 'get the prepared statements for this session',
   proname => 'pg_prepared_statement', prorows => '1000', proretset => 't',
   provolatile => 's', proparallel => 'r', prorettype => 'record',
-  proargtypes => '', proallargtypes => '{text,text,timestamptz,_regtype,bool}',
-  proargmodes => '{o,o,o,o,o}',
-  proargnames => '{name,statement,prepare_time,parameter_types,from_sql}',
+  proargtypes => '', proallargtypes => '{text,text,timestamptz,_regtype,bool,int8,int8,int8,float8,float8}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o,o}',
+  proargnames =>
'{name,statement,prepare_time,parameter_types,from_sql,calls,custom_calls,plan_generation,generic_cost,custom_cost}',
   prosrc => 'pg_prepared_statement' },
 { oid => '2511', descr => 'get the open cursors for this session',
   proname => 'pg_cursor', prorows => '1000', proretset => 't',
diff --git a/src/include/utils/plancache.h b/src/include/utils/plancache.h
index 522020d763..146eb15d34 100644
--- a/src/include/utils/plancache.h
+++ b/src/include/utils/plancache.h
@@ -124,13 +124,14 @@ typedef struct CachedPlanSource
     bool        is_complete;    /* has CompleteCachedPlan been done? */
     bool        is_saved;        /* has CachedPlanSource been "saved"? */
     bool        is_valid;        /* is the query_list currently valid? */
-    int            generation;        /* increments each time we create a plan */
+    int64        generation;        /* increments each time we create a plan */
     /* If CachedPlanSource has been saved, it is a member of a global list */
     dlist_node    node;            /* list link, if is_saved */
     /* State kept to help decide whether to use custom or generic plans: */
     double        generic_cost;    /* cost of generic plan, or -1 if not known */
     double        total_custom_cost;    /* total cost of custom plans so far */
-    int            num_custom_plans;    /* number of plans included in total */
+    int64        num_custom_plans;    /* # of custom plans included in total */
+    int64        num_total_calls;/* total number of execution */
 } CachedPlanSource;
 
 /*
diff --git a/src/test/regress/expected/prepare.out b/src/test/regress/expected/prepare.out
index 3306c696b1..b41e75c275 100644
--- a/src/test/regress/expected/prepare.out
+++ b/src/test/regress/expected/prepare.out
@@ -64,6 +64,49 @@ EXECUTE q2('postgres');
  postgres | f             | t
 (1 row)
 
+EXECUTE q2('postgres');
+ datname  | datistemplate | datallowconn 
+----------+---------------+--------------
+ postgres | f             | t
+(1 row)
+
+EXECUTE q2('postgres');
+ datname  | datistemplate | datallowconn 
+----------+---------------+--------------
+ postgres | f             | t
+(1 row)
+
+EXECUTE q2('postgres');
+ datname  | datistemplate | datallowconn 
+----------+---------------+--------------
+ postgres | f             | t
+(1 row)
+
+EXECUTE q2('postgres');
+ datname  | datistemplate | datallowconn 
+----------+---------------+--------------
+ postgres | f             | t
+(1 row)
+
+EXECUTE q2('postgres');
+ datname  | datistemplate | datallowconn 
+----------+---------------+--------------
+ postgres | f             | t
+(1 row)
+
+EXECUTE q2('postgres');
+ datname  | datistemplate | datallowconn 
+----------+---------------+--------------
+ postgres | f             | t
+(1 row)
+
+-- the view should return the correct counts
+SELECT name, calls, custom_calls, plan_generation FROM pg_prepared_statements;
+ name | calls | custom_calls | plan_generation 
+------+-------+--------------+-----------------
+ q2   |     7 |            5 |               6
+(1 row)
+
 PREPARE q3(text, int, float, boolean, smallint) AS
     SELECT * FROM tenk1 WHERE string4 = $1 AND (four = $2 OR
     ten = $3::bigint OR true = $4 OR odd = $5::int)
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index b813e32215..ff9ce88ce1 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1428,8 +1428,13 @@ pg_prepared_statements| SELECT p.name,
     p.statement,
     p.prepare_time,
     p.parameter_types,
-    p.from_sql
-   FROM pg_prepared_statement() p(name, statement, prepare_time, parameter_types, from_sql);
+    p.from_sql,
+    p.calls,
+    p.custom_calls,
+    p.plan_generation,
+    p.generic_cost,
+    p.custom_cost
+   FROM pg_prepared_statement() p(name, statement, prepare_time, parameter_types, from_sql, calls, custom_calls,
plan_generation,generic_cost, custom_cost);
 
 pg_prepared_xacts| SELECT p.transaction,
     p.gid,
     p.prepared,
diff --git a/src/test/regress/sql/prepare.sql b/src/test/regress/sql/prepare.sql
index 985d0f05c9..9d73c2fea3 100644
--- a/src/test/regress/sql/prepare.sql
+++ b/src/test/regress/sql/prepare.sql
@@ -35,6 +35,15 @@ PREPARE q2(text) AS
     FROM pg_database WHERE datname = $1;
 
 EXECUTE q2('postgres');
+EXECUTE q2('postgres');
+EXECUTE q2('postgres');
+EXECUTE q2('postgres');
+EXECUTE q2('postgres');
+EXECUTE q2('postgres');
+EXECUTE q2('postgres');
+
+-- the view should return the correct counts
+SELECT name, calls, custom_calls, plan_generation FROM pg_prepared_statements;
 
 PREPARE q3(text, int, float, boolean, smallint) AS
     SELECT * FROM tenk1 WHERE string4 = $1 AND (four = $2 OR
-- 
2.18.2