Collecting histogram diagnostics

DSE provides histogram tables for this data:

Histogram	Details table	Summary table	Keyspace details	Keyspace summary	Global details	Global summary
cell_count	Y	Y	N	N	N	N
partition_size	Y	Y	N	N	N	N
range_latency	Y	Y	Y	N	Y	N
read_latency	Y	Y	Y	N	Y	N
sstables_per_read	Y	Y	Y	N	N	N
write_latency	Y	Y	Y	N	N	N

Histogram

Details table

Summary table

Keyspace details

Keyspace summary

Global details

Global summary

cell_count

partition_size

range_latency

read_latency

sstables_per_read

write_latency

These tables show similar information to the data obtained by the nodetool tablehistograms utility. The major difference is that the nodetool histograms output is recent data, while the diagnostic tables contain lifetime data. The data in the diagnostic histogram tables is cumulative since the DSE server was started. In contrast, the nodetool tablehistograms shows the values for the past fifteen minutes.

Procedure

To enable the collection of table histogram data using the DataStax Enterprise Performance Service:
Edit the dse.yaml file.

In the dse.yaml file, set the enabled option for histogram_data_options to true.

# Column Family Histogram data tables options
histogram_data_options:
  enabled: true
  refresh_rate_ms: 10000
  retention_count: 3

(Optional) To control how often the statistics are refreshed, increase or decrease the refresh_rate_ms option in dse.yaml.

The refresh_rate_ms specifies the length of the sampling period, that is, the frequency with which this data is updated.

Collecting histogram diagnostics

Procedure

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