File statistics and tuning: Difference between revisions

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==Overview==
==Overview==
<p><var class="product">Model&nbsp;204</var> maintains a variety of utilization statistics for each user and file active during a particular run. These statistics are written to the journal, as explained in the Rocket <var class="product">Model&nbsp;204</var> System Manager's Guide, which also provides a complete description of all <var class="product">Model&nbsp;204</var> statistics.   </p>
<var class="product">Model&nbsp;204</var> maintains a variety of utilization statistics for each user and file active during a particular run. These statistics are written to the journal, as explained in [[Using system statistics#Overview|Using system statistics]], which also provides a complete description of all <var class="product">Model&nbsp;204</var> statistics.  


<p>But the journal is not the only source of statistics. You can run [[VIEW command]]s against your files to get statistics on the current file parameters and usage.<p>
But the journal is not the only source of statistics. You can run <var>[[VIEW command|VIEW]]</var> commands against your files to get statistics on the current file parameters and usage.


<p>Even if not users of the products, the manuals for the real time monitor [http://sirius-software.com/maint/download/monr.pdf SIRMON] and [http://sirius-software.com/maint/download/tunr.pdf SIRTUNE] provide useful advice on monitoring and tuning Model 204 files (as well as program and system performance as a whole).</p>
Even if not users of the products, the documentation for the real time monitor <var class="product">[[SirMon]]</var> and for <var class="product">[[SirTune]]</var> provides useful advice on monitoring and tuning Model&nbsp;204 files (as well as program and system performance as a whole).


--Journal statistics==
==Journal statistics==
<p>
For more information about using journals in system and media recovery, see [[Media recovery#Producing and archiving journals|Producing and archiving journals]].</p>


<p>For more information on using journals in system and media recovery, see [[ Media Recovery#Producing and archiving journals|Producing and archiving journals]].</p>
===When journal statistics are printed===
 
===When file statistics are printed===
<p>File statistics are kept for every file opened during the run. These statistics summarize the activity on the file for all users. File statistics normally are written to the journal when the file is closed in lines that, when printed, start with:</p>
<p>File statistics are kept for every file opened during the run. These statistics summarize the activity on the file for all users. File statistics normally are written to the journal when the file is closed in lines that, when printed, start with:</p>
<p class="code">ST $$$ FILE='<var class="term">filename</var>'
<p class="code">ST $$$ FILE='<var class="term">filename</var>'
</p>
</p>
<p>Only those statistics whose value is not zero are printed.</p>
<p>Only those statistics whose value is not zero are printed.</p>
<p>File statistics might not appear for every CLOSE command issued. When many users are working with one file, the file is kept open until the last user issues a CLOSE command. The statistics appear along with the last CLOSE. System termination prints file statistics for each file still open at the end of the run.</p>
<p>File statistics might not appear for every <var>[[CLOSE command|CLOSE]]</var> command issued. When many users are working with one file, the file is kept open until the last user issues a <var>CLOSE</var> command. The statistics appear along with the last <var>CLOSE</var>. System termination prints file statistics for each file still open at the end of the run.</p>
 
===Journal statistics summary===
<p>
In the context of file monitoring (the journal produces many other statistics useful for system tuning), these statistics ought to be of interest to the File Manager:</p>


==File statistics summary==
<table>
<table>
<tr class="head">
<tr class="head">
Line 37: Line 40:
<tr>
<tr>
<td>BXCHNG</td>
<td>BXCHNG</td>
<td>Changes to Ordered Index B-Tree entry length </td>
<td>Changes to Ordered Index B-tree entry length </td>
</tr>
</tr>
<tr>
<tr>
<td>BXDELE</td>
<td>BXDELE</td>
<td>Deletions of Ordered Index B-Tree attribute-value pair entries </td>
<td>Deletions of Ordered Index B-tree attribute-value pair entries </td>
</tr>
</tr>
<tr>
<tr>
<td>BXNEXT</td>
<td>BXNEXT</td>
<td>Lateral moves in an Ordered Index B-Tree entry range search </td>
<td>Lateral moves in an Ordered Index B-tree entry range search </td>
</tr>
</tr>
<tr>
<tr>
<td>BXFIND</td>
<td>BXFIND</td>
<td>Finds of Ordered Index B-Tree attribute-value pair entries </td>
<td>Finds of Ordered Index B-tree attribute-value pair entries </td>
</tr>
</tr>
<tr>
<tr>
<td>BXINSE</td>
<td>BXINSE</td>
<td>Inserts of new Ordered Index B-Tree attribute-value pair entries </td>
<td>Inserts of new Ordered Index B-tree attribute-value pair entries </td>
</tr>
</tr>
<tr>
<tr>
<td>BXSPLI</td>
<td>BXSPLI</td>
<td>Ordered Index B-Tree node splits, all levels </td>
<td>Ordered Index B-tree node splits, all levels </td>
</tr>
</tr>
<tr>
<tr>
<td>BXRFND</td>
<td>BXRFND</td>
<td>Ordered Index B-Tree refinds </td>
<td>Ordered Index B-tree refinds </td>
</tr>
</tr>
<tr>
<tr>
<td>BXFREE</td>
<td>BXFREE</td>
<td>Ordered Index B-Tree nodes emptied and freed </td>
<td>Ordered Index B-tree nodes emptied and freed </td>
</tr>
</tr>
<tr>
<tr>
Line 87: Line 90:
<td>
<td>
<p>Milliseconds of elapsed clock time that it has taken <var class="product">Model&nbsp;204</var> to write a file's pages to disk and to mark it "physically consistent" on disk. Includes all time spent writing pages, even if disk updates are interrupted, as indicated by the message:</p>
<p>Milliseconds of elapsed clock time that it has taken <var class="product">Model&nbsp;204</var> to write a file's pages to disk and to mark it "physically consistent" on disk. Includes all time spent writing pages, even if disk updates are interrupted, as indicated by the message:</p>
<b>M204.0440: FILE filename DISK UPDATE ABORTED</b>
<p class="code">M204.0440: FILE <i>filename</i> DISK UPDATE ABORTED</p>
</td>
</td>
</tr>
</tr>
Line 108: Line 111:
<tr>
<tr>
<td>RECDEL</td>
<td>RECDEL</td>
<td>Records, not including extension records, deleted from Table B (does not include records deleted by DELETE RECORDS or IFDSET) </td>
<td>Records, not including extension records, deleted from Table B (does not include records deleted by <var>DELETE RECORDS</var> or <var>IFDSET</var>) </td>
</tr>
</tr>
<tr>
<tr>
<td>REQ</td>
<td>REQ</td>
<td>Requests and DISPLAY commands run on the file </td>
<td>Requests and <var>DISPLAY</var> commands run on the file </td>
</tr>
</tr>
<tr>
<tr>
Line 128: Line 131:
</table>
</table>


==File Statistics==
==File statistics==
The subsections that follow demonstrate two [[VIEW command]]s that are useful for file monitoring.


Two of the [[VIEW command]]s are useful for file monitoring:
===VIEW TABLES===
<p>
A <code>VIEW TABLES</code> (or <code>V TABLES</code>) command produces output like this for the current or specified file:</p>


=== VIEW TABLES ===
<p class="code">CURFILE    ROBTEST    CURRENT FILE                             
CURLOC    (LOCAL)    CURFILE LOCATION IF REMOTE               
ASTRPPG    400        TABLE A STRINGS PER PAGE                 
ATRPG      1          TABLE A ATTRIBUTE PAGES                   
FVFPG      1          TABLE A FEW VALUED FIELD PAGES           
MVFPG      1          TABLE A MANY VALUED FIELD PAGES           
ASIZE      3          PAGES IN TABLE A                         
BSIZE      100        PAGES IN TABLE B                         
CSIZE      1          PAGES IN TABLE C                         
DSIZE      100        PAGES IN TABLE D                         
ESIZE      100        PAGES IN TABLE E                         
XSIZE      0          PAGES IN TABLE X                         
FREESIZE  888        PAGES IN FREE SPACE                       
ARETRIES  0          TABLE A PAGE RETRIES                     
BRECPPG    256        TABLE B RECORDS PER PAGE                 
XRECPPG    256        TABLE X SLOTS PER PAGE                   
BRESERVE  17          TABLE B RESERVE SPACE                     
XRESERVE  17          TABLE X RESERVE SPACE PER PAGE           
BREUSE    20          FREE SPACE REQUIRED TO REUSE TABLE B PAGE 
XREUSE    20          FREE SPACE REQUIRED TO REUSE TABLE X PAGE 
BPGPMSTR  0          TABLE B PAGES/MASTER AREA                 
BPGPOVFL  0          TABLE B PAGES/OVERFLOW AREA               
BEXTOVFL  0          TABLE B EXTRA OVERFLOW AREAS             
HIGHSORT  -1          RECORD WITH HIGHEST SORT KEY             
BLOWPG    0          TABLE B LOWEST ACTIVE PAGE               
BHIGHPG    0          TABLE B HIGHEST ACTIVE PAGE               
XHIGHPG    -1          TABLE X HIGHEST ACTIVE PAGE               
RECRDOPT  X'00'      RECORD OPTIONS                           
BRLIMSZ    0          TABLE B RECORD LIMIT SIZE                 
MSTRADD    10          RECORDS ADDED TO MASTER AREAS             
OVFLADD    0          RECORDS ADDED TO OVERFLOW AREAS           
EOVFLADD  0          RECORDS ADDED TO EXTRA OVERFLOW AREAS     
EXTNADD    0          EXTENSION RECORDS ADDED                   
MSTRDEL    0          RECORDS DELETED FROM MASTER AREAS         
OVFLDEL    0          RECORDS DELETED FROM OVERFLOW AREAS       
EOVFLDEL  0          RECORDS DELETED FROM EXT OVFLOW AREAS     
EXTNDEL    0          EXTENSION RECORDS DELETED                 
BREUSED    0          RECORDS ADDED REUSING RECORD NUMBERS     
XREUSED    0          EXTENSION SLOTS REUSED IN TABLE X         
SPILLADD  0          SPILL INDICATOR - ADDS                     
SPILLDEL  0          SPILL INDICATOR - DELETES                   
BQLEN      0          TABLE B QUEUE LENGTH                       
XQLEN      0          TABLE X QUEUE LENGTH                       
BAUTOINC  0          NUMBER OF PAGES FOR TABLE B AUTO INCREASE   
XAUTOINC  0          NUMBER OF PAGES FOR TABLE X AUTO INCREASE   
BAUTOTYP  X'00'      TABLE B AUTO INCREASE OPTIONS               
CRETRIES  0          TABLE C PAGE RETRIES                       
DHIGHPG    4          TABLE D HIGHEST PAGE USED                   
DPGSUSED  5          TABLE D PAGES IN USE                       
DPGSRES    4          TABLE D PAGES RESERVED                     
DRESERVE  15          LIST PAGE RESERVE SPACE                     
DACTIVE    0          LIST PAGE ACTIVE                           
PDSIZE    3          PAGES PER PROCEDURE DICTIONARY SECTION     
PDSTRPPG  128        NAMES/PROCEDURE DICTIONARY PAGE LIMIT       
OINODES    3          NO. ORDERED INDEX NODES: ALL LVLS           
OILEAVES  2          NO. ORDERED INDEX NODES: LEAVES             
OIDEPTH    2          NO. LEVELS OF ORDERED INDEX NODES           
OILPACT    0          ORDERED INDEX LIST PAGE ACTIVE             
OINENTRY  11          NO. ORDERED INDEX ENTRIES                   
OINBYTES  154        NO. ORDERED INDEX BYTES                     
DAUTOINC  0          NUMBER OF PAGES FOR TABLE D AUTO INCREASE   
EHIGHPG    0          TABLE E HIGHEST PAGE USED                   
EPGSUSED  0          TABLE E PAGES IN USE
</p>


<p>A VIEW (or V) TABLES command produces (for the current or specified file):</p>
===VIEW FPARMS (or FILE)===
<p>
<code>VIEW FPARMS</code> (or <code>V FPARMS</code>) command (the parameter <var>FILE</var> may be used as well) produces output like this for the current or specified file:</p>


<p class="code">
<p class="code" style="font-size:90%">CURFILE   ROBTEST   CURRENT FILE  
CURFILE   ROBTEST     CURRENT FILE                              
CURLOC     (LOCAL)   CURFILE LOCATION IF REMOTE
CURLOC   (LOCAL)     CURFILE LOCATION IF REMOTE                
FILEMODL   X'00'      (NONE) FILE MODEL ENFORCED
ASTRPPG   400        TABLE A STRINGS PER PAGE                 
FISTAT     X'00'      (OK) CURRENT STATUS OF FILE
ATRPG     1          TABLE A ATTRIBUTE PAGES                   
FICREATE  9          RELEASE 7.1 (OR BEFORE) CREATE FORMAT
FVFPG    1           TABLE A FEW VALUED FIELD PAGES           
FITRANS    8          RELEASE V2R2 TRANSFORM FORMAT
MVFPG    1          TABLE A MANY VALUED FIELD PAGES           
FIFORMAT  5          RELEASE 8.0 (OR LATER) CURRENT FPL FORMAT
ASIZE    3          PAGES IN TABLE A                         
FOPT      X'00'      FILE OPTIONS
BSIZE    100        PAGES IN TABLE B                         
FRCVOPT    X'24'      (NO CP LOGGING,NO RF LOGGING) FILE RECOVERY OPTIONS
CSIZE    1          PAGES IN TABLE C                         
OPENCTL   X'80'      (PUBLIC) OPEN CONTROL FLAGS
DSIZE    100        PAGES IN TABLE D                         
PRIVDEF   X'BFFF'    DEFAULT FILE PRIVILEGES
ESIZE    100        PAGES IN TABLE E                         
PRCLDEF    0         DEFAULT USER CLASS FOR PROCEDURES
XSIZE    0           PAGES IN TABLE X                         
SELLVL    0         DEFAULT SELECT FLS LEVEL
FREESIZE  888        PAGES IN FREE SPACE                       
READLVL    0          DEFAULT READ FLS LEVEL
ARETRIES  0          TABLE A PAGE RETRIES                     
UPDTLVL   0         DEFAULT UPDATE FLS LEVEL
BRECPPG  256        TABLE B RECORDS PER PAGE                 
ADDLVL    0          DEFAULT ADD FLS LEVEL
XRECPPG  256        TABLE X SLOTS PER PAGE                   
SECTY      X'00'      LOW-LEVEL SECURITY IN EFFECT
BRESERVE  17          TABLE B RESERVE SPACE                     
FILEORG    X'01A4'    (HALFWORD LENGTHS,REUSE RECORD NUMBERS,UNORDERED,ALL FIELDS COUNTED) FILE ORGANIZATION
XRESERVE  17          TABLE X RESERVE SPACE PER PAGE           
FIFLAGS    X'1F'      (FIELD-LEVEL CONSTRAINTS EXIST,NEW TBL C) FILE STATUS SWITCHES
BREUSE   20          FREE SPACE REQUIRED TO REUSE TABLE B PAGE 
VERIFY     X'00'      WRITE VERIFY
XREUSE   20          FREE SPACE REQUIRED TO REUSE TABLE X PAGE 
IVERIFY   X'00'     WRITE VERIFY - INITIALIZATION
BPGPMSTR  0           TABLE B PAGES/MASTER AREA                 
LANGFILE   US         LANGUAGE NAME FOR FILE
BPGPOVFL  0           TABLE B PAGES/OVERFLOW AREA               
</p>
BEXTOVFL  0           TABLE B EXTRA OVERFLOW AREAS             
HIGHSORT  -1         RECORD WITH HIGHEST SORT KEY             
BLOWPG   0           TABLE B LOWEST ACTIVE PAGE               
BHIGHPG  0           TABLE B HIGHEST ACTIVE PAGE               
XHIGHPG  -1         TABLE X HIGHEST ACTIVE PAGE               
RECRDOPT  X'00'       RECORD OPTIONS                           
BRLIMSZ  0          TABLE B RECORD LIMIT SIZE                 
MSTRADD  10          RECORDS ADDED TO MASTER AREAS             
OVFLADD  0          RECORDS ADDED TO OVERFLOW AREAS           
EOVFLADD  0          RECORDS ADDED TO EXTRA OVERFLOW AREAS      
EXTNADD  0          EXTENSION RECORDS ADDED                   
MSTRDEL  0          RECORDS DELETED FROM MASTER AREAS         
OVFLDEL  0          RECORDS DELETED FROM OVERFLOW AREAS       
EOVFLDEL  0          RECORDS DELETED FROM EXT OVFLOW AREAS     
EXTNDEL  0          EXTENSION RECORDS DELETED                 
BREUSED  0          RECORDS ADDED REUSING RECORD NUMBERS      
XREUSED  0          EXTENSION SLOTS REUSED IN TABLE X        
SPILLADD  0          SPILL INDICATOR - ADDS                     
SPILLDEL  0          SPILL INDICATOR - DELETES                   
BQLEN     0          TABLE B QUEUE LENGTH                       
XQLEN    0          TABLE X QUEUE LENGTH                       
BAUTOINC  0          NUMBER OF PAGES FOR TABLE B AUTO INCREASE   
XAUTOINC  0          NUMBER OF PAGES FOR TABLE X AUTO INCREASE    
BAUTOTYP  X'00'       TABLE B AUTO INCREASE OPTIONS               
CRETRIES  0          TABLE C PAGE RETRIES                       
DHIGHPG   4          TABLE D HIGHEST PAGE USED                   
DPGSUSED  5          TABLE D PAGES IN USE                       
DPGSRES  4          TABLE D PAGES RESERVED                     
DRESERVE  15          LIST PAGE RESERVE SPACE                     
DACTIVE  0          LIST PAGE ACTIVE                           
PDSIZE    3          PAGES PER PROCEDURE DICTIONARY SECTION     
PDSTRPPG  128         NAMES/PROCEDURE DICTIONARY PAGE LIMIT       
OINODES  3          NO. ORDERED INDEX NODES: ALL LVLS           
OILEAVES  2          NO. ORDERED INDEX NODES: LEAVES             
OIDEPTH  2          NO. LEVELS OF ORDERED INDEX NODES           
OILPACT  0          ORDERED INDEX LIST PAGE ACTIVE             
OINENTRY  11          NO. ORDERED INDEX ENTRIES                   
OINBYTES  154        NO. ORDERED INDEX BYTES                     
DAUTOINC  0          NUMBER OF PAGES FOR TABLE D AUTO INCREASE   
EHIGHPG  0          TABLE E HIGHEST PAGE USED                   
EPGSUSED  0          TABLE E PAGES IN USE
</p>                        


==Sampling the file tables==
<p>
While the <code>V TABLES</code> command broadly shows the file utilization, it is often useful when making tuning decisions to see patterns of actual usage in your files. To do this, you can use one or more of the TABLE commands (<var>[[TABLEB command|TABLEB]]</var>, <var>[[TABLEC command|TABLEC]]</var>, <var>[[TABLEE command|TABLEE]]</var>, and <var>[[TABLEX command|TABLEX]]</var> commands). There is also a special form of the <var>TABLEB</var> command:  <var>[[TABLEBX command|TABLEBX]]</var>. </p>


=== VIEW FPARMS (or FILE) ===
<p>The <var>TABLEB</var>, <var>TABLEX</var>, and <var>TABLEBX</var> commands pertain to the data, as described in the subsections below.</p> 


<p>A VIEW (or V) FPARMS (the parameter FILE may be used as well) command produces (for the current or specified file):</p>
===TABLEB command===
<p>
For small files, issuing the <var>TABLEB</var> command lets you can scan all of Table B and get a summary of the Table B usage:</p>


<p class="code">
<p class="code"><b>&gt; TABLEB</b>
CURFILE  ROBTEST    CURRENT FILE                                           
507 AVG. FREE SPACE PER PAGE
CURLOC    (LOCAL)    CURFILE LOCATION IF REMOTE                             
   2 AVG. FREE SLOTS PER PAGE
FILEMODL  X'00'      (NONE) FILE MODEL ENFORCED                             
68  NUMBER OF PAGES PROCESSED
FISTAT    X'00'      (OK) CURRENT STATUS OF FILE                             
16  BRECPPG - TABLE B RECORDS PER PAGE
FICREATE 9          RELEASE 7.1 (OR BEFORE) CREATE FORMAT                   
17  BRESERVE - TABLE B RESERVED SPACE PER PAGE
FITRANS   8          RELEASE V2R2 TRANSFORM FORMAT                           
FIFORMAT 5          RELEASE 8.0 (OR LATER) CURRENT FPL FORMAT               
FOPT      X'00'      FILE OPTIONS                                           
FRCVOPT  X'24'      (NO CP LOGGING,NO RF LOGGING) FILE RECOVERY OPTIONS     
OPENCTL  X'80'      (PUBLIC) OPEN CONTROL FLAGS                             
PRIVDEF  X'BFFF'    DEFAULT FILE PRIVILEGES                                 
PRCLDEF  0          DEFAULT USER CLASS FOR PROCEDURES                       
SELLVL    0          DEFAULT SELECT FLS LEVEL                               
READLVL  0          DEFAULT READ FLS LEVEL                                 
UPDTLVL  0          DEFAULT UPDATE FLS LEVEL                               
ADDLVL    0          DEFAULT ADD FLS LEVEL                                   
SECTY    X'00'      LOW-LEVEL SECURITY IN EFFECT                           
FILEORG  X'01A4'    (HALFWORD LENGTHS,REUSE RECORD NUMBERS,UNORDERED,ALL FIELDS COUNTED) FILE ORGANIZATION
FIFLAGS  X'1F'      (FIELD-LEVEL CONSTRAINTS EXIST,NEW TBL C) FILE STATUS SWITCHES                                     
VERIFY    X'00'      WRITE VERIFY                                           
IVERIFY  X'00'      WRITE VERIFY - INITIALIZATION                           
LANGFILE  US          LANGUAGE NAME FOR FILE                                 
</p>
</p>


<p>
For larger files, you can sample blocks of pages to get a feel for space versus slot utilization in Table B. In particular, for non <var>RRN</var> files (and, where Table X is not turned on), you can expect most of your growth toward the end of the file. So (presuming <var>BHIGHPG</var> is 117613), if you issue a command like the following:</p>


==Monitoring field retrievals in FIND statements==
<p class="code">TABLEB PAGES 117550 TO 117613</p>
<p>If you have defined a field as NON-KEY, NON-ORDERED, and NON-RANGE, you can monitor the use of the field in FIND statements using information written to the journal data set and redefine it as KEY, NUMERIC RANGE, or ORDERED when necessary.</p>
 
<p>Whenever such a field is used in a retrieval, an MS line is written to the journal with the message:</p>
<p>
<p class="code"><b></b>*** M204.0179: TABLE B SEARCH IMPLIED FOR FIELD = <var class="term">fieldname</var>
You get details for the pages specified, and a summary for those pages, something like this:</p>
 
<p class="code">PAGE NO.      FREE SPACE    FREE SLOTS   
117550            16              12
117551          1234              0
...
117613          4312              11
     
507  AVG. FREE SPACE PER PAGE
  2  AVG. FREE SLOTS PER PAGE
63  NUMBER OF PAGES PROCESSED
16  BRECPPG - TABLE B RECORDS PER PAGE
17  BRESERVE - TABLE B RESERVED SPACE PER PAGE
</p>
 
===TABLEX command===
<p>
The <var>TABLEX</var> command displays the space utilization of Table X. For example:</p>
<p class="code"><b>&gt; TABLEX</b>
479    AVG. FREE SPACE PER PAGE
18    AVG. FREE SLOTS PER PAGE
13    NUMBER OF PAGES PROCESSED
 
100    XRECPPG - TABLE X EXTENSION SLOTS PER PAGE
17    XRESERVE - TABLE X RESERVE SPACE PER PAGE
</p>
 
===TABLEBX command===
<p>
The <var>TABLEBX</var> command displays the space utilization for both Table B and Table X. For example:</p>
<p class="code"><b>&gt; TABLEBX</b>
4556  AVG. FREE SPACE PER PAGE
234    AVG. FREE SLOTS PER PAGE
2      NUMBER OF PAGES PROCESSED
 
500    BRECPPG - TABLE B RECORDS PER PAGE
17    BRESERVE - TABLE B RESERVED SPACE PER PAGE
479    AVG. FREE SPACE PER PAGE
18    AVG. FREE SLOTS PER PAGE
13    NUMBER OF PAGES PROCESSED
 
100    XRECPPG  - TABLE X EXTENSION SLOTS PERPAGE
17    XRESERVE - TABLE X RESERVE SPACE PER PAGE
</p>
<p>
You can obtain additional details regarding Tables B and X using other options of the TABLE commands, such as: </p>
<p class="code">TABLEX LIST
 
TABLEBX LIST
 
TABLEX PAGES <i>n</i> TO <i>n</i>
 
TABLEBX PAGES <i>n</i> TO <i>n</i>
</p>
 
===The RECLEN parameter and Table X===
<p>
When you use the <var>RECLEN</var> option of <var>TABLEB</var> or <var>TABLEX</var>, the output varies (as of V7R1), as follows:</p>
<p>
'''If XSIZE = 0:'''</p>
<ul>
<li><var>TABLEB RECLEN</var> generates the average logical record length,
meaning a base record and its extension records, all in Table B.</li>
 
<li><var>TABLEBX RECLEN</var> also generates the average logical record length.
<p>
In addition, <var>TABLEX RECLEN</var> generates the following message: </p>
<p class="code">***M204.2768: FILE <i>filename</i> HAS NO TABLEX PAGES</p></li>
</ul>
 
<p>
'''If XSIZE > 0:'''</p>
<ul>
<li><var>TABLEB RECLEN</var> generates the average base record length in
Table B. No Table X extension record information is included.</li>
 
<li><var>TABLEX RECLEN</var> generates the average individual extension
record length in Table X.</li>
 
<li><var>TABLEBX RECLEN</var> command generates the average logical records length,
meaning the base record in Table B and the extension records in Table X.</li>
</ul>
 
===TABLEC command===
<p>
As discussed in [[Tuning the hash index]], the output of the [[TABLEC command]] is used to drive the tuning effort. For example:</p>
 
<p class="code"><b>&gt; TABLEC</b>
M204.0638: NUMBER OF SLOTS = 102400
M204.0639: SLOTS USED = 76800
M204.0640: PERCENTAGE OF TABLE C USED = 75
M204.1833: THE TOTAL NUMBER OF PROPERTY ENTRIES IS 7496
M204.1874: THE NUMBER OF PAGES WITH SPILLS IS 33
M204.1834: 2500 PRIMARY PROPERTY ENTRIES HAVE OVERFLOW
M204.1871: THE PERCENTAGE OF PROPERTY ENTRIES WITH OVERFLOW IS 33
</p>
 
===TABLEE command===
The output of a <var>[[TABLEE command|TABLEE]]</var> command differs depending upon the <var>[[FILEORG parameter|FILEORG]]</var>, as described below.
 
====TABLEE on non FILEORG X'100' files====
<p>
In non <var>FILEORG</var> X'100' files, the <var>TABLEE</var> command is necessary to look for fragmented segments where [[File reorganization and table compaction#Dynamic data compactor for Table E|compaction]] is needed.</p> 
 
<p>The following is an example of <var>TABLEE</var> output:</p>
<p class="code"><b>&gt; IN ''filename'' TABLEE SEG</b>
M204.2817: SEGMENT:  0  NUMBER OF GAPS:  364  TOTAL GAP SIZE:  1820
M204.2817: SEGMENT:  1  NUMBER OF GAPS:  229  TOTAL GAP SIZE:  1144
M204.2815: TOTAL NUMBER OF GAPS: 593
M204.2816: TOTAL GAP SIZE: 2964
</p>
</p>
<p>This message indicates that a direct search of the data set might be required. It does not indicate whether the search was actually performed or how many records were searched (which depends on the results of any inverted conditions in the FIND statement).</p>
<p>The DIRRCD statistic provides a count of the total number of Table B records searched directly by FIND. DIRRCD appears in the journal and is accumulated by file, by user, by request, and for the entire system. DIRRCD also can be displayed by the TIME REQUEST command, described in the <var class="product">Model&nbsp;204</var> Parameter and Command Reference.    </p>


==Tuning the data holdings==
====TABLEE on FILEORG X'100' files====
<p>
Because there are neither overhead pages nor issues with gaps, in <var>FILEORG</var> X'100' files, the <var>TABLEE</var> command effectively does this:</p>
<p class="code">VIEW [[ESIZE parameter|ESIZE]] [[EHIGHPG parameter|EHIGHPG]] [[EPGSUSED parameter|EPGSUSED]]</p>


==Tuning the Ordered Index==
==Tuning==


==Tuning the Hash Index==
===Indexing decisions: Monitoring field retrievals in FIND statements===
<p>
If you have defined a field as NON-KEY, NON-ORDERED, and NON-RANGE, you can monitor the use of the field in FIND statements using information written to the journal data set and redefine it as KEY, NUMERIC RANGE, or ORDERED when necessary.</p>
<p>
Whenever such a field is used in a retrieval, an MS line is written to the journal with the message:</p>
<p class="code"><b></b>*** M204.0179: TABLE B SEARCH IMPLIED FOR FIELD = <var class="term">fieldname</var>
</p>
<p>
This message indicates that a direct search of the data set might be required. It does not indicate whether the search was actually performed or how many records were searched (which depends on the results of any inverted conditions in the FIND statement).</p>
<p>
The DIRRCD statistic provides a count of the total number of Table B records searched directly by FIND. DIRRCD appears in the journal and is accumulated by file, by user, by request, and for the entire system. DIRRCD also can be displayed by issuing <code>TIME REQUEST</code> (see the <var>[[TIME command|TIME]]</var> command).    </p>


<p>Because Table C is hashed, it can not dynamically increased, so the monitoring and tuning the hash index is critical to avoid file full conditions.</p>
===Tuning the data holdings===
<p>
Prior to the introduction of Table X (Model 204 V7R1), one of the most difficult issues with data holdings was that the  sizes of [[Record (File architecture)#Base records|base]] and [[Record (File architecture)#Extension records|extension records]] tend to differ, with the former tending to be much larger. It is also often true that, particularly in systems with a large number of updates, extension records often fragment further.</p>
<p>
Therefore, wasted slots (when <var>[[BRECPPG parameter|BRECPPG]]</var> was set high enough to support many small extensions, few base records fit on a page, which hurt index performance) were traded off with wasted space (setting a small number of slots per page meant pages with lots of extensions had lots of such space).</p>   
<p>
This tradeoff goes away when [[Table X (File architecture)|Table X]] is enabled to separate the [[Record (File architecture)#Base records|base]] and [[Record (File architecture)#Extension records|extension records]].</p>
<p>
Beyond that, the growth of <var>[[BHIGHPG parameter|BHIGHPG]]</var> (and <var>[[XHIGHPG parameter|XHIGHPG]]</var>) versus the table sizes is always something to watch. It should be the aim of the File Manager to never have files fill up. </p>


<p>To understand the underlying architecture of Table C, see [[Table C (File Architecture)]]</p>.
<p class="note"><b>Note:</b> On [[Sorted files|sorted files]], the <var>[[BEXTOVFL parameter|BEXTOVFL]]</var> parameter is of more interest, and for [[Hash key files|hash key files]], <var>BHIGHPG</var> has a quite different meaning (the number of full pages).</p>


<p>For advice on monitoring and tuning Table C, please refer to: [[Tuning the Hash Index]].
===Tuning the Ordered Index===
To understand the underlying architecture of the ordered index, see [[Table D (File architecture)#Ordered Index|Ordered Index architecture]].


For advice on setting the parameters, refer to [[Field design#ORDERED and NON-ORDERED attributes|the design of Ordered fields]].


For advice on ongoing monitoring and tuning of the Ordered Index, refer to [[Tuning the Ordered Index]].


===Tuning the hash index===
<p>
Because Table C is hashed, it cannot be dynamically increased, so monitoring and tuning the hash index is critical to avoid file full conditions.</p>


<p>To understand the underlying architecture of Table C, see [[Table C (File architecture)]].</p>


<p>For advice about monitoring and tuning Table C, refer to [[Tuning the hash index]].</p>


==Reclaiming space in files==
==Reclaiming space in files==
<p>When a VISIBLE field is redefined, renamed, or deleted, space in the various <var class="product">Model&nbsp;204</var> file tables is reclaimed for future reuse. The old name of a renamed field or the name of a deleted field is removed from Table A. If that field had the NUMERIC RANGE parameter, the auxiliary names also are removed. This also is true when a field is redefined from NUMERIC RANGE to NON-RANGE.</p>
<p>
<p>When a field name is deleted, the space used by that string in Table A is almost completely reclaimed (all but two bytes of overhead). The count of strings stored on the page is not decremented.  </p>
When a <var>VISIBLE</var> field is redefined, renamed, or deleted, space in the various <var class="product">Model&nbsp;204</var> file tables is reclaimed for future reuse. The old name of a renamed field or the name of a deleted field is removed from Table A. If that field had the <var>NUMERIC RANGE</var> attribute, the auxiliary names also are removed. This also is true when a field is redefined from <var>NUMERIC RANGE</var> to <var>NON-RANGE</var>.</p>
<p>Note</p>
<p>
<p>Value string entries for CODED and FRV fields are never removed.     </p>
When a field name is deleted, the space used by that string in Table A is almost completely reclaimed (all but two bytes of overhead). The count of strings stored on the page is not decremented.  </p>
<p>Index entries are removed from Table C for the old name of a renamed field, for a deleted field, and for redefinitions to NON-KEY, NON-RANGE, or NON-FRV.   </p>
 
<p>Index entry spaces for the old name of a renamed field in Table D are reused for the new name. Index entries are removed for deleted fields and for certain redefined fields.   </p>
<p class="note"><b>Note:</b>  
<p>Field entries in Table B are removed for deleted fields that are not preallocated. Occurrences of preallocated fields are deleted, but their space is not deleted.  </p>
Value string entries for <var>CODED</var> and <var>FRV</var> fields are never removed. </p>
<p>&nbsp;</p>
<p>
[[Category:File manager]]
Index entries are removed from Table C for the old name of a renamed field, for a deleted field, and for redefinitions to <var>NON-KEY</var>, <var>NON-RANGE</var>, or <var>NON-FRV</var>. </p>
[[Category:File management]]
<p>
Index entry spaces for the old name of a renamed field in Table D are reused for the new name. Index entries are removed for deleted fields and for certain redefined fields. </p>
<p>
Field entries in Table B are removed for deleted fields that are not preallocated. Occurrences of preallocated fields are deleted, but their space is not deleted.  </p>
 
[[Category:Model 204 files]]

Latest revision as of 22:39, 26 October 2016

Overview

Model 204 maintains a variety of utilization statistics for each user and file active during a particular run. These statistics are written to the journal, as explained in Using system statistics, which also provides a complete description of all Model 204 statistics.

But the journal is not the only source of statistics. You can run VIEW commands against your files to get statistics on the current file parameters and usage.

Even if not users of the products, the documentation for the real time monitor SirMon and for SirTune provides useful advice on monitoring and tuning Model 204 files (as well as program and system performance as a whole).

Journal statistics

For more information about using journals in system and media recovery, see Producing and archiving journals.

When journal statistics are printed

File statistics are kept for every file opened during the run. These statistics summarize the activity on the file for all users. File statistics normally are written to the journal when the file is closed in lines that, when printed, start with:

ST $$$ FILE='filename'

Only those statistics whose value is not zero are printed.

File statistics might not appear for every CLOSE command issued. When many users are working with one file, the file is kept open until the last user issues a CLOSE command. The statistics appear along with the last CLOSE. System termination prints file statistics for each file still open at the end of the run.

Journal statistics summary

In the context of file monitoring (the journal produces many other statistics useful for system tuning), these statistics ought to be of interest to the File Manager:

Term Number of...
BADD Fields added to Table B
BCHG Fields changed in place in Table B
BDEL Fields deleted from Table B
BXCHNG Changes to Ordered Index B-tree entry length
BXDELE Deletions of Ordered Index B-tree attribute-value pair entries
BXNEXT Lateral moves in an Ordered Index B-tree entry range search
BXFIND Finds of Ordered Index B-tree attribute-value pair entries
BXINSE Inserts of new Ordered Index B-tree attribute-value pair entries
BXSPLI Ordered Index B-tree node splits, all levels
BXRFND Ordered Index B-tree refinds
BXFREE Ordered Index B-tree nodes emptied and freed
DIRRCD Table B records searched
DKRD Disk reads from the file
DKWR Disk writes to the file
DUPDTS Records written to the deferred update data sets for the file
DKUPTIME

Milliseconds of elapsed clock time that it has taken Model 204 to write a file's pages to disk and to mark it "physically consistent" on disk. Includes all time spent writing pages, even if disk updates are interrupted, as indicated by the message:

M204.0440: FILE filename DISK UPDATE ABORTED

IXADD Index entries added to Tables C and D, including attempts to add duplicates
IXDEL Index entries deleted from Tables C and D
PNDGTIME Milliseconds of elapsed clock time that a file waited to be written to disk, after the last update unit completed
RECADD Records, not including extension records, started in Table B
RECDEL Records, not including extension records, deleted from Table B (does not include records deleted by DELETE RECORDS or IFDSET)
REQ Requests and DISPLAY commands run on the file
RETRYA Page retries in Table A
RETRYC Page retries in Table C
UPDTTIME Milliseconds of elapsed clock time that an open file has been part of at least one update unit

File statistics

The subsections that follow demonstrate two VIEW commands that are useful for file monitoring.

VIEW TABLES

A VIEW TABLES (or V TABLES) command produces output like this for the current or specified file:

CURFILE ROBTEST CURRENT FILE CURLOC (LOCAL) CURFILE LOCATION IF REMOTE ASTRPPG 400 TABLE A STRINGS PER PAGE ATRPG 1 TABLE A ATTRIBUTE PAGES FVFPG 1 TABLE A FEW VALUED FIELD PAGES MVFPG 1 TABLE A MANY VALUED FIELD PAGES ASIZE 3 PAGES IN TABLE A BSIZE 100 PAGES IN TABLE B CSIZE 1 PAGES IN TABLE C DSIZE 100 PAGES IN TABLE D ESIZE 100 PAGES IN TABLE E XSIZE 0 PAGES IN TABLE X FREESIZE 888 PAGES IN FREE SPACE ARETRIES 0 TABLE A PAGE RETRIES BRECPPG 256 TABLE B RECORDS PER PAGE XRECPPG 256 TABLE X SLOTS PER PAGE BRESERVE 17 TABLE B RESERVE SPACE XRESERVE 17 TABLE X RESERVE SPACE PER PAGE BREUSE 20 FREE SPACE REQUIRED TO REUSE TABLE B PAGE XREUSE 20 FREE SPACE REQUIRED TO REUSE TABLE X PAGE BPGPMSTR 0 TABLE B PAGES/MASTER AREA BPGPOVFL 0 TABLE B PAGES/OVERFLOW AREA BEXTOVFL 0 TABLE B EXTRA OVERFLOW AREAS HIGHSORT -1 RECORD WITH HIGHEST SORT KEY BLOWPG 0 TABLE B LOWEST ACTIVE PAGE BHIGHPG 0 TABLE B HIGHEST ACTIVE PAGE XHIGHPG -1 TABLE X HIGHEST ACTIVE PAGE RECRDOPT X'00' RECORD OPTIONS BRLIMSZ 0 TABLE B RECORD LIMIT SIZE MSTRADD 10 RECORDS ADDED TO MASTER AREAS OVFLADD 0 RECORDS ADDED TO OVERFLOW AREAS EOVFLADD 0 RECORDS ADDED TO EXTRA OVERFLOW AREAS EXTNADD 0 EXTENSION RECORDS ADDED MSTRDEL 0 RECORDS DELETED FROM MASTER AREAS OVFLDEL 0 RECORDS DELETED FROM OVERFLOW AREAS EOVFLDEL 0 RECORDS DELETED FROM EXT OVFLOW AREAS EXTNDEL 0 EXTENSION RECORDS DELETED BREUSED 0 RECORDS ADDED REUSING RECORD NUMBERS XREUSED 0 EXTENSION SLOTS REUSED IN TABLE X SPILLADD 0 SPILL INDICATOR - ADDS SPILLDEL 0 SPILL INDICATOR - DELETES BQLEN 0 TABLE B QUEUE LENGTH XQLEN 0 TABLE X QUEUE LENGTH BAUTOINC 0 NUMBER OF PAGES FOR TABLE B AUTO INCREASE XAUTOINC 0 NUMBER OF PAGES FOR TABLE X AUTO INCREASE BAUTOTYP X'00' TABLE B AUTO INCREASE OPTIONS CRETRIES 0 TABLE C PAGE RETRIES DHIGHPG 4 TABLE D HIGHEST PAGE USED DPGSUSED 5 TABLE D PAGES IN USE DPGSRES 4 TABLE D PAGES RESERVED DRESERVE 15 LIST PAGE RESERVE SPACE DACTIVE 0 LIST PAGE ACTIVE PDSIZE 3 PAGES PER PROCEDURE DICTIONARY SECTION PDSTRPPG 128 NAMES/PROCEDURE DICTIONARY PAGE LIMIT OINODES 3 NO. ORDERED INDEX NODES: ALL LVLS OILEAVES 2 NO. ORDERED INDEX NODES: LEAVES OIDEPTH 2 NO. LEVELS OF ORDERED INDEX NODES OILPACT 0 ORDERED INDEX LIST PAGE ACTIVE OINENTRY 11 NO. ORDERED INDEX ENTRIES OINBYTES 154 NO. ORDERED INDEX BYTES DAUTOINC 0 NUMBER OF PAGES FOR TABLE D AUTO INCREASE EHIGHPG 0 TABLE E HIGHEST PAGE USED EPGSUSED 0 TABLE E PAGES IN USE

VIEW FPARMS (or FILE)

VIEW FPARMS (or V FPARMS) command (the parameter FILE may be used as well) produces output like this for the current or specified file:

CURFILE ROBTEST CURRENT FILE CURLOC (LOCAL) CURFILE LOCATION IF REMOTE FILEMODL X'00' (NONE) FILE MODEL ENFORCED FISTAT X'00' (OK) CURRENT STATUS OF FILE FICREATE 9 RELEASE 7.1 (OR BEFORE) CREATE FORMAT FITRANS 8 RELEASE V2R2 TRANSFORM FORMAT FIFORMAT 5 RELEASE 8.0 (OR LATER) CURRENT FPL FORMAT FOPT X'00' FILE OPTIONS FRCVOPT X'24' (NO CP LOGGING,NO RF LOGGING) FILE RECOVERY OPTIONS OPENCTL X'80' (PUBLIC) OPEN CONTROL FLAGS PRIVDEF X'BFFF' DEFAULT FILE PRIVILEGES PRCLDEF 0 DEFAULT USER CLASS FOR PROCEDURES SELLVL 0 DEFAULT SELECT FLS LEVEL READLVL 0 DEFAULT READ FLS LEVEL UPDTLVL 0 DEFAULT UPDATE FLS LEVEL ADDLVL 0 DEFAULT ADD FLS LEVEL SECTY X'00' LOW-LEVEL SECURITY IN EFFECT FILEORG X'01A4' (HALFWORD LENGTHS,REUSE RECORD NUMBERS,UNORDERED,ALL FIELDS COUNTED) FILE ORGANIZATION FIFLAGS X'1F' (FIELD-LEVEL CONSTRAINTS EXIST,NEW TBL C) FILE STATUS SWITCHES VERIFY X'00' WRITE VERIFY IVERIFY X'00' WRITE VERIFY - INITIALIZATION LANGFILE US LANGUAGE NAME FOR FILE

Sampling the file tables

While the V TABLES command broadly shows the file utilization, it is often useful when making tuning decisions to see patterns of actual usage in your files. To do this, you can use one or more of the TABLE commands (TABLEB, TABLEC, TABLEE, and TABLEX commands). There is also a special form of the TABLEB command: TABLEBX.

The TABLEB, TABLEX, and TABLEBX commands pertain to the data, as described in the subsections below.

TABLEB command

For small files, issuing the TABLEB command lets you can scan all of Table B and get a summary of the Table B usage:

> TABLEB 507 AVG. FREE SPACE PER PAGE 2 AVG. FREE SLOTS PER PAGE 68 NUMBER OF PAGES PROCESSED 16 BRECPPG - TABLE B RECORDS PER PAGE 17 BRESERVE - TABLE B RESERVED SPACE PER PAGE

For larger files, you can sample blocks of pages to get a feel for space versus slot utilization in Table B. In particular, for non RRN files (and, where Table X is not turned on), you can expect most of your growth toward the end of the file. So (presuming BHIGHPG is 117613), if you issue a command like the following:

TABLEB PAGES 117550 TO 117613

You get details for the pages specified, and a summary for those pages, something like this:

PAGE NO. FREE SPACE FREE SLOTS 117550 16 12 117551 1234 0 ... 117613 4312 11 507 AVG. FREE SPACE PER PAGE 2 AVG. FREE SLOTS PER PAGE 63 NUMBER OF PAGES PROCESSED 16 BRECPPG - TABLE B RECORDS PER PAGE 17 BRESERVE - TABLE B RESERVED SPACE PER PAGE

TABLEX command

The TABLEX command displays the space utilization of Table X. For example:

> TABLEX 479 AVG. FREE SPACE PER PAGE 18 AVG. FREE SLOTS PER PAGE 13 NUMBER OF PAGES PROCESSED 100 XRECPPG - TABLE X EXTENSION SLOTS PER PAGE 17 XRESERVE - TABLE X RESERVE SPACE PER PAGE

TABLEBX command

The TABLEBX command displays the space utilization for both Table B and Table X. For example:

> TABLEBX 4556 AVG. FREE SPACE PER PAGE 234 AVG. FREE SLOTS PER PAGE 2 NUMBER OF PAGES PROCESSED 500 BRECPPG - TABLE B RECORDS PER PAGE 17 BRESERVE - TABLE B RESERVED SPACE PER PAGE 479 AVG. FREE SPACE PER PAGE 18 AVG. FREE SLOTS PER PAGE 13 NUMBER OF PAGES PROCESSED 100 XRECPPG - TABLE X EXTENSION SLOTS PERPAGE 17 XRESERVE - TABLE X RESERVE SPACE PER PAGE

You can obtain additional details regarding Tables B and X using other options of the TABLE commands, such as:

TABLEX LIST TABLEBX LIST TABLEX PAGES n TO n TABLEBX PAGES n TO n

The RECLEN parameter and Table X

When you use the RECLEN option of TABLEB or TABLEX, the output varies (as of V7R1), as follows:

If XSIZE = 0:

  • TABLEB RECLEN generates the average logical record length, meaning a base record and its extension records, all in Table B.
  • TABLEBX RECLEN also generates the average logical record length.

    In addition, TABLEX RECLEN generates the following message:

    ***M204.2768: FILE filename HAS NO TABLEX PAGES

If XSIZE > 0:

  • TABLEB RECLEN generates the average base record length in Table B. No Table X extension record information is included.
  • TABLEX RECLEN generates the average individual extension record length in Table X.
  • TABLEBX RECLEN command generates the average logical records length, meaning the base record in Table B and the extension records in Table X.

TABLEC command

As discussed in Tuning the hash index, the output of the TABLEC command is used to drive the tuning effort. For example:

> TABLEC M204.0638: NUMBER OF SLOTS = 102400 M204.0639: SLOTS USED = 76800 M204.0640: PERCENTAGE OF TABLE C USED = 75 M204.1833: THE TOTAL NUMBER OF PROPERTY ENTRIES IS 7496 M204.1874: THE NUMBER OF PAGES WITH SPILLS IS 33 M204.1834: 2500 PRIMARY PROPERTY ENTRIES HAVE OVERFLOW M204.1871: THE PERCENTAGE OF PROPERTY ENTRIES WITH OVERFLOW IS 33

TABLEE command

The output of a TABLEE command differs depending upon the FILEORG, as described below.

TABLEE on non FILEORG X'100' files

In non FILEORG X'100' files, the TABLEE command is necessary to look for fragmented segments where compaction is needed.

The following is an example of TABLEE output:

> IN filename TABLEE SEG M204.2817: SEGMENT: 0 NUMBER OF GAPS: 364 TOTAL GAP SIZE: 1820 M204.2817: SEGMENT: 1 NUMBER OF GAPS: 229 TOTAL GAP SIZE: 1144 M204.2815: TOTAL NUMBER OF GAPS: 593 M204.2816: TOTAL GAP SIZE: 2964

TABLEE on FILEORG X'100' files

Because there are neither overhead pages nor issues with gaps, in FILEORG X'100' files, the TABLEE command effectively does this:

VIEW ESIZE EHIGHPG EPGSUSED

Tuning

Indexing decisions: Monitoring field retrievals in FIND statements

If you have defined a field as NON-KEY, NON-ORDERED, and NON-RANGE, you can monitor the use of the field in FIND statements using information written to the journal data set and redefine it as KEY, NUMERIC RANGE, or ORDERED when necessary.

Whenever such a field is used in a retrieval, an MS line is written to the journal with the message:

*** M204.0179: TABLE B SEARCH IMPLIED FOR FIELD = fieldname

This message indicates that a direct search of the data set might be required. It does not indicate whether the search was actually performed or how many records were searched (which depends on the results of any inverted conditions in the FIND statement).

The DIRRCD statistic provides a count of the total number of Table B records searched directly by FIND. DIRRCD appears in the journal and is accumulated by file, by user, by request, and for the entire system. DIRRCD also can be displayed by issuing TIME REQUEST (see the TIME command).

Tuning the data holdings

Prior to the introduction of Table X (Model 204 V7R1), one of the most difficult issues with data holdings was that the sizes of base and extension records tend to differ, with the former tending to be much larger. It is also often true that, particularly in systems with a large number of updates, extension records often fragment further.

Therefore, wasted slots (when BRECPPG was set high enough to support many small extensions, few base records fit on a page, which hurt index performance) were traded off with wasted space (setting a small number of slots per page meant pages with lots of extensions had lots of such space).

This tradeoff goes away when Table X is enabled to separate the base and extension records.

Beyond that, the growth of BHIGHPG (and XHIGHPG) versus the table sizes is always something to watch. It should be the aim of the File Manager to never have files fill up.

Note: On sorted files, the BEXTOVFL parameter is of more interest, and for hash key files, BHIGHPG has a quite different meaning (the number of full pages).

Tuning the Ordered Index

To understand the underlying architecture of the ordered index, see Ordered Index architecture.

For advice on setting the parameters, refer to the design of Ordered fields.

For advice on ongoing monitoring and tuning of the Ordered Index, refer to Tuning the Ordered Index.

Tuning the hash index

Because Table C is hashed, it cannot be dynamically increased, so monitoring and tuning the hash index is critical to avoid file full conditions.

To understand the underlying architecture of Table C, see Table C (File architecture).

For advice about monitoring and tuning Table C, refer to Tuning the hash index.

Reclaiming space in files

When a VISIBLE field is redefined, renamed, or deleted, space in the various Model 204 file tables is reclaimed for future reuse. The old name of a renamed field or the name of a deleted field is removed from Table A. If that field had the NUMERIC RANGE attribute, the auxiliary names also are removed. This also is true when a field is redefined from NUMERIC RANGE to NON-RANGE.

When a field name is deleted, the space used by that string in Table A is almost completely reclaimed (all but two bytes of overhead). The count of strings stored on the page is not decremented.

Note: Value string entries for CODED and FRV fields are never removed.

Index entries are removed from Table C for the old name of a renamed field, for a deleted field, and for redefinitions to NON-KEY, NON-RANGE, or NON-FRV.

Index entry spaces for the old name of a renamed field in Table D are reused for the new name. Index entries are removed for deleted fields and for certain redefined fields.

Field entries in Table B are removed for deleted fields that are not preallocated. Occurrences of preallocated fields are deleted, but their space is not deleted.