2026-03-12 20:23:15

vdh/big_table_read_perf.sql

@@ -0,0 +1,63 @@
+set lines 150
+set pages 9999
+set feedback off
+set echo off
+
+select distinct sid from v$mystat;
+alter system flush buffer_cache;
+
+alter session set "_serial_direct_read"='always';
+
+--exec dbms_monitor.session_trace_enable(waits => true)
+
+DECLARE
+
+    l_cnt           number;
+    l_start_value   number;
+    l_end_value     number;
+    l_diff          number;
+    l_start         timestamp;
+    l_end           timestamp;
+    l_elapsed       number;
+    l_throughput    number;
+
+BEGIN
+
+    select value
+    into l_start_value
+    from v$mystat mystat, v$statname statname
+    where mystat.statistic# = statname.statistic#
+          and statname.name = 'physical read bytes';
+         
+    l_start := systimestamp;
+
+    select /*+ FULL(A) PARALLEL(A,10) */ count(*) into l_cnt from sysadm.COMLONG A;
+    -- select /*+ FULL(A) NOPARALLEL(A) */ count(*) into l_cnt from sysadm.COMLONG A;
+    -- select /*+ FULL(A) */ count(*) into l_cnt from c2mv5.hist_act A;
+
+    l_end := systimestamp;
+
+    
+    select value
+    into l_end_value
+    from v$mystat mystat, v$statname statname
+    where mystat.statistic# = statname.statistic#
+          and statname.name = 'physical read bytes';   
+
+    l_elapsed :=  extract(day from (l_end - l_start)) * 24 * 60 * 60
+                  + extract(hour from (l_end - l_start)) * 60 * 60
+                  + extract(minute from (l_end - l_start)) * 60
+                  + extract(second from (l_end - l_start));
+    l_diff := (l_end_value - l_start_value);
+    l_throughput := (l_diff/l_elapsed)/1024/1024;
+    
+    dbms_output.put_line('physical MB read: ' || to_char(l_diff/1024/1024, '999G999G999D99'));
+    dbms_output.put_line('elapsed seconds: ' || to_char(l_elapsed, '9G999G999D99'));
+    dbms_output.put_line('measured throughput: ' || to_char(l_throughput, '999G999D99'));
+
+END;
+/
+
+--exec dbms_monitor.session_trace_disable();
+
+