Displays a statistical summary that can be used for optimization.
High-performance Sort/Merge: The high-performance Sort/Merge
utility suppports only the following statistics: Records read,
Records sorted, Records output, and Input record length.
Format
/STATISTICS
1 – Full Description
When the /STATISTICS qualifier is used, Sort/Merge displays
statistics in SYS$OUTPUT. You can use these statistics to
judge the efficiency of the ordering operation and to determine
adjustments that can improve its performance. To save these
statistics in a file, specify the following command:
$ DEFINE/USER SYS$ERROR output-file
High-performance Sort/Merge: The high-performance Sort/Merge
utility displays only the following statistics: Records read,
Records sorted, Records output, and Input record length.
The following statistical display results when you use the
/STATISTICS qualifier:
OpenVMS Sort/Merge Statistics
Records read: nnn Input record length: nnn
Records sorted: nnn Internal length: nnn
Records output: nnn Output record length: nnn
Working set extent: nnn Sort tree size: nnn
Virtual memory: nnn Number of initial runs: nnn
Direct I/O: nnn Maximum merge order: nnn
Buffered I/O: nnn Number of merge passes: nnn
Page faults: nnn Work file allocation: nnn
Elapsed time: nn:nn:nn.nn Elapsed CPU: nn:nn:nn.nn
Records read is the number of records read by Sort or Merge.
Records sorted is the number of records that have been processed
using Sort. This number could be less than the number of records
read if a specification file is used to select only certain
records for the sort or merge operation.
Records output is the number of records written to the output
file. This number could be less than the number of records sorted
if /NODUPLICATES was selected or if I/O errors occurred when the
output records were being written.
Working set extent shows the number of pages in the process
working set extent. This value is used as an upper limit on the
size of the sort data structure. Adjusting this value is one way
to improve the efficiency of a sort operation.
Virtual memory is the number of pages of virtual memory added to
the Sort image to hold the data.
The total of the direct I/O and buffered I/O is the number of
I/O movements needed to read and write data. The lower this total
value is, the more efficient the ordering operation.
The number of page faults indicates how well the data fits into
memory: the higher the number of page faults, the less efficient
the ordering operation.
Elapsed time is the total wall clock time used by the sort or
merge operation in hours, minutes, seconds, and hundredths of
seconds.
The input record length value is obtained from the Record
Management Services (OpenVMS RMS) unless the user supplies it.
Internal length is the size in bytes of an internal format node.
This includes any keys, data, a word to store the length, record
file addresses (RFAs), and converted keys.
Output record length is the length of the output record. The
length is computed from the input record length, the sort
process, and the record reformatting requested.
Sort tree size is the number of records that fit in sort's
internal data structure.
Number of initial runs is one indication of how well the data
fits into memory.
The maximum merge order is the maximum number of sorted strings
that are merged at one time.
The number of merge passes is the number of times the Sort
utility merges strings until one sorted output string is
produced. The number of initial runs and the number of merge
passes indicate how well the data fits in memory. The higher
these numbers, the further the working set size is from
containing the data and the longer the sorting takes.
Work file allocation is the number of blocks used for the work
files. When more than one merge pass is needed, this size is
approximately twice the size of the input file allocation.
Elapsed CPU is the CPU time used by the ordering operation;
it does not include time spent waiting for I/O operations to
complete or time spent waiting while another process executes.
2 – Example
$ SORT/STATISTICS PRICE1.DAT,PRICE2.DAT PRICE.LIS
This SORT command results in the following statistical display:
OpenVMS Sort/Merge Statistics
Records read: 793 Input record length: 80
Records sorted: 793 Internal length: 80
Records output: 793 Output record length: 80
Working set extent: 100 Sort tree size: 412
Virtual memory: 433 Number of initial runs: 2
Direct I/O: 22 Maximum merge order: 2
Buffered I/O: 9 Number of merge passes: 1
Page faults: 3418 Work file allocation: 114
Elapsed time: 00:00:05.98 Elapsed CPU: 00:00:03.63
In the sample statistics display, the Sort data structure
size is limited by the small working set extent. By doubling
the working set extent you can almost double the Sort data
structure size, enabling all the records to fit in memory
without using work files.