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Monitoring Block Collisions Using ^BLKCOL

A block collision occurs when a process is forced to wait for access to a block. Excessive block collisions slow application performance.

Using ^BLKCOL

The ^BLKCOL utility samples block collisions over a specified period (10 seconds by default), recording the latest block collision within a specified interval (10 milliseconds by default) during this time. For each recorded collision, ^BLKCOL identifies not only the block, but the global involved and its first and last references in the block, as well as the routine and line that created the process attempting to access the block.
Note:
The cstat -D option, as described in Running cstat with Options in the “Monitoring Caché Using the cstat Utility” appendix of this guide, also samples block collisions, but identifies only the blocks involved.
The output of cstat -D is included in the reports generated by the ^pButtons utility, as described in the Monitoring Performance Using ^pButtons chapter of this guide.
When running ^BLKCOL, you can specify the following:
  • The length of the sampling period in seconds
  • The interval between samples in milliseconds
  • Whether to collect routine details (default is yes)
  • Whether to format the output as
    • a list of the blocks with the highest collision counts (default)
    • a list of all blocks involved in collisions
    • comma-separated values from all block collisions detected, sorted and counted by block number and routine
    • comma-separated values from all block collisions detected, unsorted (raw)
    • a list of collision hot spots in routines
  • the number of blocks to display (if applicable)
  • whether to send output to a file

^BLKCOL Ouput

Use of the ^BLKCOL utility is shown in the following sample terminal session:
%SYS>d ^BLKCOL

Block Collision Analysis

How many seconds should we sample: <10>
How long to wait (ms) between each sample: <10>
Collect routine details? <Y>
Format for 'T'op counts, 'D'isplay all, 'S'orted CSV, 'H'ot spot, or 'R'aw CSV: <T>
Number of blocks to display: <10>
Output to file: <0>

Sampling ... (any key to interrupt)


625 block collisions in 735 samples.

Block # (count) - Global refs (first - last in block) - Routine refs (SFN)

767       (395) in c:\mycache\mgr\user\
  ^acctest - ^acctest(10220," 167") (T/BPtr)
    325 at ^AccessTest+156(4)
    25 at ^AccessTest+121(4)
    24 at ^AccessTest+92(4)
    8 at ^AccessTest+109(4)
    8 at ^AccessTest+127(4)
    4 at ^AccessTest+170(4)
    1 at ^AccessTest+163(4)

3890      (11)  in c:\mycache\mgr\user\
  ^acctest(2552,"  371") - ^acctest(2552,"  38") (Data)
    6 at ^AccessTest+164(4)
    3 at ^AccessTest+163(4)
    1 at ^AccessTest+134(4)
    1 at ^AccessTest+156(4)

15572     (9)   in c:\mycache\mgr\user\
  ^acctest(6980," 4795") - ^acctest(6988," 3259") (Data)
    7 at ^AccessTest+134(4)
    1 at ^AccessTest+164(4)
    1 at ^AccessTest+170(4)

15818     (8)   in c:\mycache\mgr\user\
  ^acctest(9124," 173") - ^acctest(9124," 1743") (Data)
    5 at ^AccessTest+164(4)
    3 at ^AccessTest+170(4)

971       (7)   in c:\mycache\mgr\user\
  ^acctest(484," 3927") - ^acctest(484," 3938") (Data)
    5 at ^AccessTest+170(4)
    2 at ^AccessTest+164(4)

1137      (7)   in c:\mycache\mgr\user\
  ^acctest(756," 4063") - ^acctest(756," 4073") (Data)
    3 at ^AccessTest+109(4)
    2 at ^AccessTest+134(4)
    1 at ^AccessTest+156(4)
    1 at ^AccessTest+163(4)

2999      (7)   in c:\mycache\mgr\user\
  ^acctest(2092,"  666") - ^acctest(2092,"  674") (Data)
    3 at ^AccessTest+170(4)
    1 at ^AccessTest+109(4)
    1 at ^AccessTest+121(4)
    1 at ^AccessTest+134(4)
    1 at ^AccessTest+164(4)

6173      (7)   in c:\mycache\mgr\user\
  ^acctest(3684,"  528") - ^acctest(3684,"  536") (Data)
    3 at ^AccessTest+163(4)
    1 at ^AccessTest+109(4)
    1 at ^AccessTest+156(4)
    1 at ^AccessTest+164(4)
    1 at ^AccessTest+170(4)

14617     (7)   in c:\mycache\mgr\user\
  ^acctest(9688,"   18") - ^acctest(9688,"   26") (Data)
    4 at ^AccessTest+170(4)
    2 at ^AccessTest+164(4)
    1 at ^AccessTest+134(4)

15282     (7)   in c:\mycache\mgr\user\
  ^acctest(8700," 4889") - ^acctest(8760," 1402") (Data)
    4 at ^AccessTest+170(4)
    3 at ^AccessTest+164(4)
%SYS>d ^BLKCOL

Block Collision Analysis

How many seconds should we sample: <10>
How long to wait (ms) between each sample: <10>
Collect routine details? <Y>
Format for 'T'op counts, 'D'isplay all, 'S'orted CSV, 'H'ot spot, or 'R'aw CSV: <T> H
Number of blocks to display: <10>
Output to file: <0>

Sampling ... (any key to interrupt)


571 block collisions in 768 samples.

 
Sorted by routine/line that waits for block ownership
_____________________________________________________

(571) AccessTest
    (324) +156^AccessTest :  s @G@($J,node)=$$getdata($E(Str,1,$r(1000)))  ;SMLXXX+, AFH
    (54) +164^AccessTest :  k @G@($J,node)
    (43) +134^AccessTest :  .  k @G@($J,node)
    (31) +92^AccessTest :  .  .  k @G@($j)
    (28) +109^AccessTest :  .  s x=$O(@G@($J,x))

Sorted by routine that owns the block
_____________________________________

(472) AccessTest
    (472) +AccessTest

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