Use EnableQueryId()

So that the user don't have to explicitly set compute_query_id to "on"
to make it work.

README.md

@@ -57,6 +57,13 @@ The extension can be disabled with the `pg_query_settings.enabled` parameter.
 More informations on pg_query_settings
 --------------------------------------
 
+Load the library :
+
+```
+postgres=# LOAD 'pg_query_settings';
+LOAD
+```
+
 Create the extension:
 
 ```
@@ -73,14 +80,6 @@ postgres=# INSERT INTO toto SELECT i, 'Ligne '||i FROM generate_series(1, 100000
 INSERT 0 10000000
 ```
 
-In order to retrieve the query id, you'll probably need to enable the
-`compute_query_id` parameter in the same session :
-
-```
-postgres=# SET compute_query_id TO on;
-SET
-``` 
-
 We run a query that uses a sort :
 
 ```
@@ -146,36 +145,6 @@ INSERT 0 1
 
 We execute the query :
 
-```
-postgres=# EXPLAIN (COSTS OFF, ANALYZE, SETTINGS, VERBOSE) SELECT * FROM toto ORDER BY c2;
-┌────────────────────────────────────────────────────────────────────────────────────┐
-│ QUERY PLAN │
-├────────────────────────────────────────────────────────────────────────────────────┤
-│ Sort (actual time=29046.787..41640.526 rows=10000000 loops=1) │
-│ Output: c1, c2 │
-│ Sort Key: toto.c2 │
-│ Sort Method: external merge Disk: 272920kB │
-│ -> Seq Scan on public.toto (actual time=0.035..12971.535 rows=10000000 loops=1) │
-│ Output: c1, c2 │
-│ Settings: random_page_cost = '1.1' │
-│ Query Identifier: 2507635424379213761 │
-│ Planning Time: 0.162 ms │
-│ Execution Time: 53110.755 ms │
-└────────────────────────────────────────────────────────────────────────────────────┘
-(10 rows)
-```
-
-Our configuration is not applied. That's OK, the library isn't loaded.
-
-We load the library :
-
-```
-postgres=# LOAD 'pg_query_settings';
-LOAD
-```
-
-We execute the query again:
-
 ```
 postgres=# EXPLAIN (COSTS OFF, ANALYZE, SETTINGS, VERBOSE) SELECT * FROM toto ORDER BY c2;
 WARNING: queryid is '2507635424379213761'

pg_query_settings.c

@@ -18,6 +18,13 @@
 #include <catalog/namespace.h>
 #include <miscadmin.h>
 #include <executor/executor.h>
+
+#if (PG_VERSION_NUM >= 140000) && (PG_VERSION_NUM < 160000)
+#include <utils/queryjumble.h>
+#elif (PG_VERSION_NUM >= 160000)
+#include <nodes/queryjumble.h>
+#endif
+
 #include <optimizer/planner.h>
 #include <storage/bufmgr.h>
 #include <utils/builtins.h>
@@ -351,6 +358,11 @@ _PG_init(void)
  MarkGUCPrefixReserved("pg_query_settings");
 #endif
 
+#if PG_VERSION_NUM >= 140000
+ /* Inform core that we require a query identifier to be computed */
+ EnableQueryId();
+#endif
+
  if (debug) elog(DEBUG1,"Entering _PG_init()");
 
  /* Set our two hooks */