findhash

FindHash

This tool brute forces instance values for the default hash algorithm used with carbon-relay.py. The idea is to discover a solution where the spread between the number of buckets on the hash ring associated with each hash ring member is the smallest. This should produce a more even distribution of metrics through the cluster.

This serves (presently) no purpose for the Jump style hash ring.

Original Author: Jack Neely jjneely@42lines.net 2017/04/24

Step #1

Generate a template file. This is a text file of SERVER:INSTANCE pairs separated by newlines. Unknown instance values are left out (but not the trailing colon).

Example:

graphite-data-001:cb6f1823-126b-4fd6-9071-4c8b8392d9c8
graphite-data-002:310e3cb4-1457-4fc4-8f5c-196437f8801c
graphite-data-003:cf009318-5915-403a-bb1d-4c9a06907e06
graphite-data-004:01510bf1-d82d-4b73-9e93-9e967bd0bb36
graphite-data-005:

Save this text file.

Step #2

Run findhash with this text file as the sole argument.

$ ./findhash testme
Possible solution:
        Max buckets per host: 13310
        Min buckets per host: 12980
        graphite-data-002:310e3cb4-1457-4fc4-8f5c-196437f8801c
        graphite-data-004:01510bf1-d82d-4b73-9e93-9e967bd0bb36
        graphite-data-003:cf009318-5915-403a-bb1d-4c9a06907e06
        graphite-data-001:cb6f1823-126b-4fd6-9071-4c8b8392d9c8
        graphite-data-005:fd8581de-1505-4d81-a10b-d1214e4356b6
Possible solution:
        Max buckets per host: 13291
        Min buckets per host: 12984
        graphite-data-003:cf009318-5915-403a-bb1d-4c9a06907e06
        graphite-data-005:bef765eb-d0e6-4c10-ad94-6fe651397bea
        graphite-data-001:cb6f1823-126b-4fd6-9071-4c8b8392d9c8
        graphite-data-002:310e3cb4-1457-4fc4-8f5c-196437f8801c
        graphite-data-004:01510bf1-d82d-4b73-9e93-9e967bd0bb36
Possible solution:
        Max buckets per host: 13182
        Min buckets per host: 12997
        graphite-data-004:01510bf1-d82d-4b73-9e93-9e967bd0bb36
        graphite-data-003:cf009318-5915-403a-bb1d-4c9a06907e06
        graphite-data-001:cb6f1823-126b-4fd6-9071-4c8b8392d9c8
        graphite-data-002:310e3cb4-1457-4fc4-8f5c-196437f8801c
        graphite-data-005:5ed781bb-8482-4aae-bfa5-76c9570d89bf

Results will continue as they are found. The -max and -min options will filter the results so that the range of buckets per host are within the given min and/or max.

The -filter option will filter the result output as to only show the servers matching the prefix passed to the -filter option.

Step #3

Complete your hashring member file with the chosen solution so that the defined hashring is complete. Use the -analyze option to print a basic analysis of the hashring.

$ ./findhash -analyze testme
Node graphite-data-001:cb6f1823-126b-4fd6-9071-4c8b8392d9c8:    13121
Node graphite-data-002:310e3cb4-1457-4fc4-8f5c-196437f8801c:    13086
Node graphite-data-003:cf009318-5915-403a-bb1d-4c9a06907e06:    13182
Node graphite-data-004:01510bf1-d82d-4b73-9e93-9e967bd0bb36:    13149
Node graphite-data-005:5ed781bb-8482-4aae-bfa5-76c9570d89bf:    12997

Ideal bucket count per server: 13107.00
Spread: 13182 - 12997 = 185
Deviation: 63.4445

Step #4

Build a list of Graphite metric keys and run an analysis on how they map to nodes in the given hashring. The list is newline separated. This is a sub function of the -analyze function.

$ ./findhash -analyze -keys ood-test-metrics testme
Node graphite-data-001:cb6f1823-126b-4fd6-9071-4c8b8392d9c8:    13121
Node graphite-data-002:310e3cb4-1457-4fc4-8f5c-196437f8801c:    13086
Node graphite-data-003:cf009318-5915-403a-bb1d-4c9a06907e06:    13182
Node graphite-data-004:01510bf1-d82d-4b73-9e93-9e967bd0bb36:    13149
Node graphite-data-005:5ed781bb-8482-4aae-bfa5-76c9570d89bf:    12997

Ideal bucket count per server: 13107.00
Spread: 13182 - 12997 = 185
Deviation: 63.4445
Keys per node:
graphite-data-001:cb6f1823-126b-4fd6-9071-4c8b8392d9c8  141
graphite-data-002:310e3cb4-1457-4fc4-8f5c-196437f8801c  146
graphite-data-003:cf009318-5915-403a-bb1d-4c9a06907e06  172
graphite-data-004:01510bf1-d82d-4b73-9e93-9e967bd0bb36  161
graphite-data-005:5ed781bb-8482-4aae-bfa5-76c9570d89bf  139

Total Metric Keys: 759
Ideal keys per node: 151.80
Deviation: 12.7028