{
  "date": "2014-10-15T05:13:08",
  "slug": "oracle-system-statistics-display-auxstats-with-calculated-values-and-formulas",
  "link": "https://www.dbi-services.com/blog/oracle-system-statistics-display-auxstats-with-calculated-values-and-formulas/",
  "title": {
    "rendered": "Oracle system statistics: Display AUX_STATS$ with calculated values and formulas"
  },
  "content": {
    "rendered": "<h2>By Franck Pachot</h2>\n<p>.<br />\nSystem statistics can be gathered in NOWORKLOAD or WORKLOAD mode. Different values will be set depending on that and the others will be calculated &#8211; derived from them. We can see defined values from SYS.AUX_STATS$ but here is a script that shows the calculated ones as well.</p>\n<p>With no system statistics or NOWORKLOAD the values of IOSEEKTIM (latency in ms) and IOTFRSPEED (transfer in bytes/ms) are set and the SREADTIM (time to read 1 block in ms) and MREADTIM (for multiblock read) are calculated from them. MBRC depends on the defaults or the db_file_multiblock_read_count settings.</p>\n<p>With WORKLOAD statistics, the SREADTIM and MREADTIM as well as MBRC are measured and those are the ones that are used by the optimizer.</p>\n<p>Here is my script:</p>\n<pre><code>set echo off\nset linesize 200 pagesize 1000\ncolumn pname format a30\ncolumn sname format a20\ncolumn pval2 format a20\nselect pname,pval2 from sys.aux_stats$ where sname='SYSSTATS_INFO';\nselect pname,pval1,calculated,formula from sys.aux_stats$ where sname='SYSSTATS_MAIN'\nmodel\n  reference sga on (\n    select name,value from v$sga \n        ) dimension by (name) measures(value)\n  reference parameter on (\n    select name,decode(type,3,to_number(value)) value from v$parameter where name='db_file_multiblock_read_count' and ismodified!='FALSE'\n    union all\n    select name,decode(type,3,to_number(value)) value from v$parameter where name='sessions'\n    union all\n    select name,decode(type,3,to_number(value)) value from v$parameter where name='db_block_size'\n        ) dimension by (name) measures(value)\npartition by (sname) dimension by (pname) measures (pval1,pval2,cast(null as number) as calculated,cast(null as varchar2(60)) as formula) rules(\n  calculated['MBRC']=coalesce(pval1['MBRC'],parameter.value['db_file_multiblock_read_count'],parameter.value['_db_file_optimizer_read_count'],8),\n  calculated['MREADTIM']=coalesce(pval1['MREADTIM'],pval1['IOSEEKTIM'] + (parameter.value['db_block_size'] * calculated['MBRC'] ) / pval1['IOTFRSPEED']),\n  calculated['SREADTIM']=coalesce(pval1['SREADTIM'],pval1['IOSEEKTIM'] + parameter.value['db_block_size'] / pval1['IOTFRSPEED']),\n  calculated['   multi block Cost per block']=round(1/calculated['MBRC']*calculated['MREADTIM']/calculated['SREADTIM'],4),\n  calculated['   single block Cost per block']=1,\n  formula['MBRC']=case when pval1['MBRC'] is not null then 'MBRC' when parameter.value['db_file_multiblock_read_count'] is not null then 'db_file_multiblock_read_count' when parameter.value['_db_file_optimizer_read_count'] is not null then '_db_file_optimizer_read_count' else '= _db_file_optimizer_read_count' end,\n  formula['MREADTIM']=case when pval1['MREADTIM'] is null then '= IOSEEKTIM + db_block_size * MBRC / IOTFRSPEED' end,\n  formula['SREADTIM']=case when pval1['SREADTIM'] is null then '= IOSEEKTIM + db_block_size        / IOTFRSPEED' end,\n  formula['   multi block Cost per block']='= 1/MBRC * MREADTIM/SREADTIM',\n  formula['   single block Cost per block']='by definition',\n  calculated['   maximum mbrc']=sga.value['Database Buffers']/(parameter.value['db_block_size']*parameter.value['sessions']),\n  formula['   maximum mbrc']='= buffer cache size in blocks / sessions'\n);\nset echo on</code></pre>\n<p>Here is an exemple with <strong>default statistics</strong>:</p>\n<pre><code>PNAME                               PVAL1 CALCULATED FORMULA\n------------------------------ ---------- ---------- --------------------------------------------------\nCPUSPEEDNW                           1519\nIOSEEKTIM                              10\nIOTFRSPEED                           4096\nSREADTIM                                          12 = IOSEEKTIM + db_block_size        / IOTFRSPEED\nMREADTIM                                          26 = IOSEEKTIM + db_block_size * MBRC / IOTFRSPEED\nCPUSPEED\nMBRC                                               8 = _db_file_optimizer_read_count\nMAXTHR\nSLAVETHR\n   maximum mbrc                           117.152542 = buffer cache size in blocks / sessions\n   single block Cost per block                     1 by definition\n   multi block Cost per block                  .2708 = 1/MBRC * MREADTIM/SREADTIM\n</code></pre>\n<p>You see the calculated values for everything. Note the &#8216;maximum mbrc&#8217; which limits the multiblock reads when the buffer cache is small. It divides the buffer cache size (at startup &#8211; can depend on ASMM and AMM settings) by the sessions parameter.</p>\n<p>Here is an example with <strong>workload system statistics</strong> gathering:</p>\n<pre><code>PNAME                               PVAL1 CALCULATED FORMULA\n------------------------------ ---------- ---------- --------------------------------------------------\nCPUSPEEDNW                           1511\nIOSEEKTIM                              15\nIOTFRSPEED                           4096\nSREADTIM                            1.178      1.178\nMREADTIM                              .03        .03\nCPUSPEED                             3004\nMBRC                                    8          8 MBRC\nMAXTHR                            6861824\nSLAVETHR\n   maximum mbrc                           114.983051 = buffer cache size in blocks / sessions\n   single block Cost per block                     1 by definition\n   multi block Cost per block                  .0032 = 1/MBRC * MREADTIM/SREADTIM\n</code></pre>\n<p>here all values are explicitly set (added after comment from Raul: those are probably completely wrong as MREADTIM should be &gt; SREADTIM)</p>\n<p>And an example with <strong>exadata system statistics</strong> that defines noworkload values and sets also the MBRC (see <a href=\"http://antognini.ch/2013/10/system-statistics-gathered-in-exadata-mode-when-are-they-relevant/#trackback\">Chris Antognini post</a> about it)</p>\n<pre><code>PNAME                               PVAL1 CALCULATED FORMULA\n------------------------------ ---------- ---------- --------------------------------------------------\nCPUSPEEDNW                           1539\nIOSEEKTIM                              16\nIOTFRSPEED                         204800\nSREADTIM                                       16.04 = IOSEEKTIM + db_block_size        / IOTFRSPEED\nMREADTIM                                       18.28 = IOSEEKTIM + db_block_size * MBRC / IOTFRSPEED\nCPUSPEED\nMBRC                                   57         57 MBRC\nMAXTHR\nSLAVETHR\n   maximum mbrc                           114.983051 = buffer cache size in blocks / sessions\n   single block Cost per block                     1 by definition\n   multi block Cost per block                    .02 = 1/MBRC * MREADTIM/SREADTIM\n</code></pre>\n<p>And finally here is a <strong>workload system statistics </strong>result but with explicitly setting the db_file_multiblock_read_count to 128:</p>\n<pre><code>PNAME                               PVAL1 CALCULATED FORMULA\n------------------------------ ---------- ---------- --------------------------------------------------\nCPUSPEEDNW                           1539\nIOSEEKTIM                              15\nIOTFRSPEED                           4096\nSREADTIM                                          17 = IOSEEKTIM + db_block_size        / IOTFRSPEED\nMREADTIM                                         271 = IOSEEKTIM + db_block_size * MBRC / IOTFRSPEED\nCPUSPEED\nMBRC                                             128 db_file_multiblock_read_count\nMAXTHR\nSLAVETHR\n   maximum mbrc                           114.983051 = buffer cache size in blocks / sessions\n   single block Cost per block                     1 by definition\n   multi block Cost per block                  .1245 = 1/MBRC * MREADTIM/SREADTIM\n</code></pre>\n<p>Here you see that the MBRC in noworkload is coming from the value which is set by the db_file_multiblock_read_count rather from the value 8 which is used by default by the optimizer when it is not set. And the MREADTIM is calculated from that i/o size</p>\n<p>For more historical information about system statistics and how multiblock reads are costed (index vs. full table scan choice) see my article on latest <a href=\"http://viewer.zmags.com/publication/a8a4c4aa#/a8a4c4aa/62#54\">OracleScene</a></p>\n<p>As usual, if you find anything to improve in that script, please share.</p>\n",
    "protected": false
  }
}