Monitor chunks and dbspaces to determine how full and how active each entity is. The read and write statistics for chunks and dbspaces can help determine whether data use is evenly distributed across table fragments. Use the following command-line options to monitor chunks and dbspaces.
If you suspect that one or two specific coservers are creating performance problems, you can monitor chunks and read and write calls for each fragment on one coserver at a time.
Query the sysfragments system catalog table for the names of tables that reside in a chunk, as described in Examining Information in the sysfragments System Catalog Table.
The xctl onstat -D command displays the following information for each chunk in a dbspace:
Figure 7 shows sample output from the xctl onstat -D option.
... Dbspaces address number flags fchunk nchunks flags owner name a10d5a0 1 1 1 1 N informix rootdbs1 a10d628 3 1 3 1 N informix customer_dbsl.1 a10d6b0 5 1 5 1 N informix period_dbsl.1 a10d738 7 1 7 1 N informix product_dbsl.1 4 active, 32768 maxiumum (if CONFIGSIZE is LARGE) Chunks address chk/dbs offset page Rd page Wr pathname a108c30 1 1 0 74 12 /dev/rdsk/c0t1d0s6 a108d60 3 3 0 53 0 /dev/custdbsl.1 a108e90 5 5 50000 3 0 /dev/perdbsl.1 a108fc0 7 7 55000 481 0 /dev/proddbsl.1 4 active, 32768 maxiumum (if CONFIGSIZE is LARGE)
To determine the name of the dbspace to which a chunk belongs, match the number in the dbs field of the Chunks section with the number in the number field of the Dbspaces section. For example, the page Rd field in this output shows that chunk 7, which is the only chunk in dbspace 7, has a disproportionately higher number of page reads (481) compared to the other dbspaces.
For information about free pages in chunks, execute xctl onstat -d.
The xctl onstat -g iof option displays the number of reads from and writes to each dbspace or file. This option is similar to the -D option, except that it also displays information on nonchunk files. It includes information about temporary files and sort-work files.
Use this option to monitor the distribution of I/O requests for the different fragments of a table. If one chunk has a disproportionate amount of I/O activity, it might be a system bottleneck.
The sample output in Figure 8 shows that the disk reads and disk writes are not balanced across the different dbspaces.
... AIO global files: gfd pathname totalops dskread dskwrite io/s 3 rootdbs1 86 74 12 0.2 4 /dev/custdbsl.1 53 53 0 0.1 5 /dev/perdbsl.1 3 3 0 0.0 6 /dev/proddbsl.1 481 481 0 0.9 7 /dev/dbsl.1 89 89 0 0.2 ... AIO global files: gfd pathname totalops dskread dskwrite io/s 3 rootdbs2 73 62 11 1.0 4 /dev/custdbsl.2 30 30 0 0.1 5 /dev/perdbsl.2 3 3 0 0.0 6 /dev/proddbsl.2 483 483 0 0.9 7 /dev/dbsl.2 89 89 0 0.2
Figure 8 shows the following that the chunks whose path name is /dev/proddbsl.1 on the first coserver and /dev/proddbsl.2 on the second coserver have a disproportionately high number of disk reads compared to the other chunks.
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