Monitoring Smart Flash Cache on the database servers is very limited as only one metric is available from V$SYSSTAT that records flash cache activity -- "cell flash cache read hits". On the other hand monitoring the Smart Flash Cache from the storage servers provides more detail and diagnostic data, although there is no way to monitor the full storage tier from a single location, thus the statistics are for the portion of the total flash cache on the given storage server.
Storage Server Tools
Through the CellCLI utility a number of statistics are available to monitor flash cache usage. You can view the metrics and their descriptions using the LIST METRICDEFINITION command. To return the flash cache metrics and their descriptions the following command can be used:
CellCLI> list metricdefinition attributes name, description where objectType = 'FLASHCACHE'
The metrics and descriptions are listed in Table 1:
FC_BYKEEP_OVERWR "Number of megabytes pushed out of the FlashCache because of space limit for 'keep' objects"
FC_BYKEEP_OVERWR_SEC "Number of megabytes per second pushed out of the FlashCache because of space limit for 'keep' objects"
FC_BYKEEP_USED "Number of megabytes used for 'keep' objects on FlashCache"
FC_BY_USED "Number of megabytes used on FlashCache"
FC_IO_BYKEEP_R "Number of megabytes read from FlashCache for 'keep' objects"
FC_IO_BYKEEP_R_SEC "Number of megabytes read per second from FlashCache for 'keep' objects"
FC_IO_BYKEEP_W "Number of megabytes written to FlashCache for 'keep' objects"
FC_IO_BYKEEP_W_SEC "Number of megabytes per second written to FlashCache for 'keep' objects"
FC_IO_BY_R "Number of megabytes read from FlashCache"
FC_IO_BY_R_MISS "Number of megabytes read from disks because not all requested data was in FlashCache"
FC_IO_BY_R_MISS_SEC "Number of megabytes read from disks per second because not all requested data was in FlashCache"
FC_IO_BY_R_SEC "Number of megabytes read per second from FlashCache"
FC_IO_BY_R_SKIP "Number of megabytes read from disks for IO requests that bypass FlashCache"
FC_IO_BY_R_SKIP_SEC "Number of megabytes read from disks per second for IO requests that bypass FlashCache"
FC_IO_BY_W "Number of megabytes written to FlashCache"
FC_IO_BY_W_SEC "Number of megabytes per second written to FlashCache"
FC_IO_ERRS "Number of IO errors on FlashCache"
FC_IO_RQKEEP_R "Number of read IO requests for 'keep' objects satisfied from FlashCache"
FC_IO_RQKEEP_R_MISS "Number of read IO requests for 'keep' objects which did not find all data in FlashCache"
FC_IO_RQKEEP_R_MISS_SEC "Number of read IO requests per second for 'keep' objects which did not find all data in FlashCache"
FC_IO_RQKEEP_R_SEC "Number of read IO requests for 'keep' objects per second satisfied from FlashCache"
FC_IO_RQKEEP_R_SKIP "Number of read IO requests for 'keep' objects that bypass FlashCache"
FC_IO_RQKEEP_R_SKIP_SEC "Number of read IO requests per second for 'keep' objects that bypass FlashCache"
FC_IO_RQKEEP_W "Number of IO requests for 'keep' objects which resulted in FlashCache being populated with data"
FC_IO_RQKEEP_W_SEC "Number of IO requests per second for 'keep' objects which resulted in FlashCache being populated with data"
FC_IO_RQ_R "Number of read IO requests satisfied from FlashCache"
FC_IO_RQ_R_MISS "Number of read IO requests which did not find all data in FlashCache"
FC_IO_RQ_R_MISS_SEC "Number of read IO requests per second which did not find all data in FlashCache"
FC_IO_RQ_R_SEC "Number of read IO requests satisfied per second from FlashCache"
FC_IO_RQ_R_SKIP "Number of read IO requests that bypass FlashCache"
FC_IO_RQ_R_SKIP_SEC "Number of read IO requests per second that bypass FlashCache"
FC_IO_RQ_W "Number of IO requests which resulted in FlashCache being populated with data"
FC_IO_RQ_W_SEC "Number of IO requests per second which resulted in FlashCache being populated with data"
Table 1 Storage Cell Flash Cache Metrics and Their Descriptions
These metrics are cumulative from the time cellsrv was started. To list the current value for one or more of the metrics the LIST METRICCURRENT statement is used. The output reports the cumulative statistics for a single storage cell; the same command will need to be run on all remaining storage cells to monitor the activity for the entire Smart Flash Cache.
Using the LIST METRICCURRENT statement to return Smart Flash Cache metrics for the given storage cell:
CellCLI> list metriccurrent where objectType = 'FLASHCACHE'
FC_BYKEEP_OVERWR FLASHCACHE 0.000 MB
FC_BYKEEP_OVERWR_SEC FLASHCACHE 0.000 MB/sec
FC_BYKEEP_USED FLASHCACHE 0.000 MB
FC_BY_USED FLASHCACHE 365,322 MB
FC_IO_BYKEEP_R FLASHCACHE 0.000 MB
FC_IO_BYKEEP_R_SEC FLASHCACHE 0.000 MB/sec
FC_IO_BYKEEP_W FLASHCACHE 0.047 MB
FC_IO_BYKEEP_W_SEC FLASHCACHE 0.000 MB/sec
FC_IO_BY_R FLASHCACHE 60,257,512 MB
FC_IO_BY_R_MISS FLASHCACHE 12,592,252 MB
FC_IO_BY_R_MISS_SEC FLASHCACHE 0.891 MB/sec
FC_IO_BY_R_SEC FLASHCACHE 21.193 MB/sec
FC_IO_BY_R_SKIP FLASHCACHE 567,179,945 MB
FC_IO_BY_R_SKIP_SEC FLASHCACHE 3.681 MB/sec
FC_IO_BY_W FLASHCACHE 22,170,046 MB
FC_IO_BY_W_SEC FLASHCACHE 4.028 MB/sec
FC_IO_ERRS FLASHCACHE 0
FC_IO_RQKEEP_R FLASHCACHE 0 IO requests
FC_IO_RQKEEP_R_MISS FLASHCACHE 0 IO requests
FC_IO_RQKEEP_R_MISS_SEC FLASHCACHE 0.0 IO/sec
FC_IO_RQKEEP_R_SEC FLASHCACHE 0.0 IO/sec
FC_IO_RQKEEP_R_SKIP FLASHCACHE 0 IO requests
FC_IO_RQKEEP_R_SKIP_SEC FLASHCACHE 0.0 IO/sec
FC_IO_RQKEEP_W FLASHCACHE 3 IO requests
FC_IO_RQKEEP_W_SEC FLASHCACHE 0.0 IO/sec
FC_IO_RQ_R FLASHCACHE 6,638,504,145 IO requests
FC_IO_RQ_R_MISS FLASHCACHE 373,704,323 IO requests
FC_IO_RQ_R_MISS_SEC FLASHCACHE 28.5 IO/sec
FC_IO_RQ_R_SEC FLASHCACHE 2,688 IO/sec
FC_IO_RQ_R_SKIP FLASHCACHE 1,010,237,424 IO requests
FC_IO_RQ_R_SKIP_SEC FLASHCACHE 16.7 IO/sec
FC_IO_RQ_W FLASHCACHE 1,096,872,236 IO requests
FC_IO_RQ_W_SEC FLASHCACHE 326 IO/sec
Metrics for objects where the storage clause sets CELL_FLASH_CACHE to KEEP can be isolated and reported; for example:
CellCLI> list metriccurrent where objectType = 'FLASHCACHE' and name like '.*KEEP.*'
FC_BYKEEP_OVERWR FLASHCACHE 0.000 MB
FC_BYKEEP_OVERWR_SEC FLASHCACHE 0.000 MB/sec
FC_BYKEEP_USED FLASHCACHE 0.000 MB
FC_IO_BYKEEP_R FLASHCACHE 0.000 MB
FC_IO_BYKEEP_R_SEC FLASHCACHE 0.000 MB/sec
FC_IO_BYKEEP_W FLASHCACHE 0.047 MB
FC_IO_BYKEEP_W_SEC FLASHCACHE 0.000 MB/sec
FC_IO_RQKEEP_R FLASHCACHE 0 IO requests
FC_IO_RQKEEP_R_MISS FLASHCACHE 0 IO requests
FC_IO_RQKEEP_R_MISS_SEC FLASHCACHE 0.0 IO/sec
FC_IO_RQKEEP_R_SEC FLASHCACHE 0.0 IO/sec
FC_IO_RQKEEP_R_SKIP FLASHCACHE 0 IO requests
FC_IO_RQKEEP_R_SKIP_SEC FLASHCACHE 0.0 IO/sec
FC_IO_RQKEEP_W FLASHCACHE 3 IO requests
FC_IO_RQKEEP_W_SEC FLASHCACHE 0.0 IO/sec
CellCLI>
It is also possible to exclude those same metrics by changing the statement slightly:
CellCLI> list metriccurrent where objectType = 'FLASHCACHE' and name not like '.*KEEP.*'
FC_BY_USED FLASHCACHE 365,290 MB
FC_IO_BY_R FLASHCACHE 60,267,646 MB
FC_IO_BY_R_MISS FLASHCACHE 12,592,880 MB
FC_IO_BY_R_MISS_SEC FLASHCACHE 1.568 MB/sec
FC_IO_BY_R_SEC FLASHCACHE 23.065 MB/sec
FC_IO_BY_R_SKIP FLASHCACHE 567,186,500 MB
FC_IO_BY_R_SKIP_SEC FLASHCACHE 5.888 MB/sec
FC_IO_BY_W FLASHCACHE 22,171,791 MB
FC_IO_BY_W_SEC FLASHCACHE 2.865 MB/sec
FC_IO_ERRS FLASHCACHE 0
FC_IO_RQ_R FLASHCACHE 6,639,787,345 IO requests
FC_IO_RQ_R_MISS FLASHCACHE 373,724,226 IO requests
FC_IO_RQ_R_MISS_SEC FLASHCACHE 50.2 IO/sec
FC_IO_RQ_R_SEC FLASHCACHE 2,927 IO/sec
FC_IO_RQ_R_SKIP FLASHCACHE 1,010,251,273 IO requests
FC_IO_RQ_R_SKIP_SEC FLASHCACHE 19.4 IO/sec
FC_IO_RQ_W FLASHCACHE 1,096,966,059 IO requests
FC_IO_RQ_W_SEC FLASHCACHE 170 IO/sec
CellCLI>
Performance metrics aren't the only values collected for the Smart Flash Cache; you can see what is in the cache using the LIST FLASHCACHECONTENT command. To see which attributes are available to view or that can be used to filter the output, the FLASHCACHECONTENT object can be described:
CellCLI> describe flashcachecontent
cachedKeepSize
cachedSize
dbID
dbUniqueName
hitCount
hoursToExpiration
missCount
objectNumber
tableSpaceNumber
A specific database can be targeted using either dbUniqueName or dbID. The objectNumber and tableSpaceNumber attributes are specific to a given dbUniqueName/dbID so they should be used in conjunction with either dbUniqueName or dbID. To view the unique database name, the object number, the KEEP size, the cache size, the hit count and miss count for objects from the DBM database the command would be as follows:
CellCLI> list flashcachecontent where dbUniqueName = 'DBM' and hitcount > 99 attributes dbUniqueName, objectNumber, cachedKeepSize, cachedSize, hitcount, misscount
DBM 2 0 172032 1889 350
DBM 8 0 81920 168 7
DBM 104 0 622592 170 48
DBM 225 0 2654208 382 247
DBM 227 0 1081344 173 77
DBM 268 0 1859584 770 25
DBM 271 0 65536 298 5
DBM 272 0 65536 383 4
DBM 421 0 2064384 8120 772
DBM 424 0 589824 2391 63
DBM 425 0 122880 372 17
DBM 466 0 196608 612 37
DBM 469 0 131072 462 4
DBM 474 0 1114112 4130 193
DBM 476 0 3194880 730 734
DBM 477 0 10780672 17240 9525
DBM 478 0 2482176 327 956
DBM 5823 0 229376 107 4
DBM 5830 0 819200 295 147
DBM 5831 0 4268032 8869 1366
DBM 5847 0 319488 382 42
DBM 5849 0 262144 105 16
DBM 5853 0 90112 160 21
DBM 5857 0 843776 246 129
DBM 5886 0 1966080 2568 1640
DBM 5888 0 688128 152 187
DBM 5907 0 245760 147 8
DBM 5908 0 163840 597 56
DBM 5910 0 393216 1079 56
DBM 5911 0 98304 238 44
DBM 5912 0 983040 1367 1122
DBM 6173 0 98304 142 13
DBM 6175 0 131072 190 10
DBM 6176 0 65536 145 26
DBM 6304 0 65536 165 2
DBM 6305 0 65536 254 13
DBM 6312 0 262144 772 33
DBM 6313 0 196608 739 23
DBM 6316 0 196608 614 17
DBM 6317 0 172032 743 38
DBM 6331 0 262144 533 16
DBM 6335 0 65536 302 4
DBM 6337 0 131072 500 3
DBM 6339 0 458752 993 94
DBM 6343 0 196608 573 7
DBM 6345 0 131072 418 4
DBM 6357 0 1245184 3988 468
DBM 6358 0 131072 362 34
DBM 6365 0 188416 260 34
DBM 6366 0 262144 500 55
DBM 6397 0 262144 867 51
DBM 6398 0 1474560 4901 688
DBM 6399 0 458752 1182 83
DBM 6400 0 262144 845 47
DBM 6415 0 131072 533 3
DBM 6423 0 196608 607 18
DBM 6424 0 262144 1105 30
DBM 6425 0 131072 447 4
DBM 6426 0 131072 490 23
DBM 6427 0 196608 724 6
DBM 6428 0 65536 273 4
DBM 6429 0 458752 1290 116
DBM 6430 0 65536 235 8
DBM 6433 0 196608 592 17
DBM 6435 0 262144 843 21
DBM 6436 0 196608 757 32
DBM 6437 0 131072 522 5
DBM 6443 0 163840 625 11
DBM 6445 0 131072 441 7
DBM 6447 0 131072 475 3
DBM 6494 0 65536 126 11
DBM 6503 0 65536 234 2
DBM 6506 0 3129344 7564 1976
DBM 6507 0 11337728 26885 6736
DBM 6508 0 3096576 8290 1615
DBM 6509 0 1310720 4752 397
DBM 6515 0 393216 930 114
DBM 6522 0 131072 475 3
DBM 6524 0 131072 474 3
DBM 6544 0 262144 883 12
DBM 6546 0 131072 331 6
DBM 6549 0 131072 399 7
DBM 6585 0 2220032 5603 1695
DBM 6586 0 1310720 4282 526
DBM 6588 0 114688 457 14
DBM 6589 0 131072 423 4
DBM 6591 0 262144 785 25
DBM 6592 0 131072 398 19
DBM 6593 0 131072 498 4
DBM 6594 0 131072 541 10
DBM 6595 0 131072 318 25
DBM 6605 0 65536 161 1
DBM 6607 0 131072 483 3
DBM 6656 0 1794048 165 55
DBM 12718 0 262144 340 33
DBM 12728 0 98304 234 14
DBM 12730 0 1196032 1919 520
DBM 12736 0 327680 614 36
DBM 18752 0 65536 166 1
DBM 20411 0 1900544 3824 675
DBM 23052 0 319488 77860 4
DBM 23053 0 1695744 259114 19595
DBM 23055 0 131072 37872 26
DBM 23056 0 49152 43335 5
DBM 23057 0 114688 43392 12
DBM 47869 0 262144 138 15
DBM 48001 0 360448 169 23
DBM 48125 0 360448 154 14
DBM 48185 0 622592 180 257
DBM 48264 0 286720 103 62
DBM 48306 0 32768 242 120
DBM 48406 0 196608 102 12
DBM 48464 0 237568 116 110
DBM 48466 0 1220608 247 104
DBM 48663 0 802816 142 52
DBM 48705 0 917504 101 20
DBM 48840 0 2334720 170 31
DBM 48972 0 2138112 176 104
DBM 4294967294 0 376832 25674712 181405
CellCLI>
By default the LIST FLASHCACHECONTENT command reports the dbID, tableSpaceNumber and objectNumber. To return other attributes they need to be listed in the command, using the attributes clause, as was done in this example.
Notice that among all of the attributes available at the storage cell level the object name is not one of them. This can easily be reported from the database servers by querying DBA_OBJECTS using the objectNumber reported by CellCLI, which maps to the DATA_OBJECT_ID column:
SQL> select owner, object_type, object_name
2 from dba_objects
3 where data_object_id = 5888;
OWNER OBJECT_TYPE OBJECT_NAME
-------------------- ------------------- --------------------------------
SYS INDEX WRI$_ADV_MSG_GRPS_IDX_01
SQL>
A script can be written to generate the output from the LIST FLASHCACHECONTENT command and place it into a text file on the database server, for example:
/usr/bin/ssh celladmin@myexa1cel01-priv.7-11.com "CellCLI -e list flashcachecontent where dbUniqueName = '$1' attributes dbUniquename,objectNumber,hitcount,misscount,cachedSize"
/usr/bin/ssh celladmin@myexa1cel02-priv.7-11.com "CellCLI -e list flashcachecontent where dbUniqueName = '$1' attributes dbUniquename,objectNumber,hitcount,misscount,cachedSize"
/usr/bin/ssh celladmin@myexa1cel03-priv.7-11.com "CellCLI -e list flashcachecontent where dbUniqueName = '$1' attributes dbUniquename,objectNumber,hitcount,misscount,cachedSize"
A second script would be used to execute the first script and send the output to a file:
/home/oracle/bin/CellCLI_flashcache_mon_nohdrs.sh $1 > /home/oracle/ext_tbls/flash_mon.txt
The database name of interest is passed to the second script on the command line. The generated file can then be used to create an external table, which can be joined to the DBA_OBJECTS view to report Smart Flash Cache activity by object name. As an example:
SQL> create or replace directory admin_dat_dir as '/home/oracle/ext_tbls';
Directory created.
SQL> create or replace directory admin_log_dir as '/home/oracle/logs';
Directory created.
SQL> create or replace directory admin_bad_dir as '/home/oracle/bad';
Directory created.
SQL>
SQL> CREATE TABLE flashmon_ext
2 (db_name varchar2(12),
3 object_id number,
4 hitct number,
5 missct number,
6 cachesz number
7 )
8 ORGANIZATION EXTERNAL
9 (
10 TYPE ORACLE_LOADER
11 DEFAULT DIRECTORY admin_dat_dir
12 ACCESS PARAMETERS
13 (
14 records delimited by newline
15 badfile admin_bad_dir:'flashmon_ext%a_%p.bad'
16 logfile admin_log_dir:'flashmon_ext%a_%p.log'
17 fields terminated by whitespace
18 missing field values are null
19 ( db_name, object_id, hitct, missct, cachesz
20 )
21 )
22 LOCATION ('flash_mon.txt')
23 )
24 PARALLEL
25 REJECT LIMIT UNLIMITED;
Table created.
SQL>
The first directory contains the text file generated from CellCLI and the LIST FLASHCACHECONTENT command. The next two directories are for the logfile and badfile which could be generated by SQL*Loader. Finally we create the external table; since the text file shouldn't change names or locations generating a new file won't cause the external table to become invalid. Thus the data can be refreshed at any time and the external table will still be usable.
After the external table is created it's a simple task of writing the query to map object_name to object_id:
SQL> select f.db_name, o.object_name, f.hitct, f.missct, f.cachesz
2 from flashmon_ext f left outer join dba_objects o on (o.data_object_id = f.object_id);
DB_NAME OBJECT_NAME HITCT MISSCT CACHESZ
------------ ----------------------------------- ---------- ---------- ----------
DBM1 ICOL$ 407479 9163 40828928
DBM1 ICOL$ 425912 11731 59179008
DBM1 ICOL$ 575450 44509 31588352
DBM1 I_USER1 33 4 32768
DBM1 CON$ 159 60 32768
DBM1 CON$ 447 67 98304
DBM1 UNDO$ 49 2 32768
DBM1 C_COBJ# 4782 572 2129920
DBM1 C_COBJ# 9077 984 3178496
DBM1 C_COBJ# 8120 968 4358144
DBM1 I_OBJ# 2320 65 557056
DBM1 I_OBJ# 1323 17 327680
DBM1 I_OBJ# 1742 30 327680
DBM1 I_IND1 280 19 458752
DBM1 I_IND1 1160 44 196608
DBM1 I_IND1 1405 35 131072
DBM1 I_CDEF2 6150 516 425984
DBM1 I_CDEF2 1332 78 720896
DBM1 I_CDEF2 3483 210 2031616
DBM1 I_OBJ5 49088 2555 9732096
DBM1 I_OBJ5 16742 1144 8192000
.....
In this example the flashmon_ext table contains 16,202 rows since data was collected across all three available storage cells. This explains the apparent duplication of object names in the output; each storage cell can cache the same object at the same time. Even though the object names may be duplicated, the cache size, hit count, and miss count are usually different.
It is not unusual to find object_id values in the four billion range, and these object_ids won't match to any object in DBA_OBJECTS. One source of object_ids in that range would be the V$FIXED_TABLE and GV$FIXED_TABLE views, however none of the listed object_id values in the flashmon_ext table in that range match any of those objects. In the absence of global temporary tables the objects in question are undo segments.
Database Server Tools
There isn't much to see at the database layer, unfortunately. A single statistic, "cell flash cache read hits", is all that is available. Like the other matrics this is cumulative, since the instance started as reported in V$SYSSTAT and for the duration of the current session in V$MYSTAT. The easiest way to measure the Smart Flash Cache activity for a SQL statement is to query V$MYSTAT before and after the statement is executed. Doing this in SQL*Plus offers the ability to save the query results in variables for use after the statement has completed, as follows:
SQL> select statistic#, value
2 from v$mystat
3 where statistic# in (select statistic# from v$statname where name = 'cell flash cache read hits');
STATISTIC# VALUE
---------- ----------
605 1
SQL>
SQL> select count(*)
2 from emp;
COUNT(*)
----------
7340032
SQL>
SQL> column val new_value endval
SQL>
SQL> select statistic#, value val
2 from v$mystat
3 where statistic# in (select statistic# from v$statname where name = 'cell flash cache read hits');
STATISTIC# VAL
---------- ----------
605 857
SQL>
SQL>
SQL> select &endval - &beginval flash_hits
2 from dual;
FLASH_HITS
----------
856
SQL>
With a bit of effort and preparation on the DBA's part, monitoring the Smart Flash Cache can be fairly easy. If the time is taken to also establish user equivalence between nodes and storage cells, the process can be automated via cron to provide hourly updates to measure performance of the Smart Flash Cache. It's a performance enhancement with Exadata you really want to have working at its peak, and the methods described here can help you do just that.
See all articles by David Fitzjarrell
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