[CASSANDRA-12729] Cassandra-Stress: Use single seed in UUID generation

• Type: Bug
• Status: Resolved
• Priority: Low
• Resolution: Fixed
• Fix Version/s: 3.10
• Component/s: Legacy/Tools
• Severity: Low
• Assignee: Chris Splinter
• Reporter: Chris Splinter

Authors

Chris Splinter

Reviewers

T Jake Luciani

• Created: 28/Sep/16 23:47
• Updated: 16/Apr/19 09:30
• Resolved: 10/Oct/16 13:53

Description

While testing the new sequence distribution for the user module of cassandra-stress I noticed that half of the expected rows (848 / 1696) were produced when using a single uuid primary key.

table: player_info_by_uuid
table_definition: |
  CREATE TABLE player_info_by_uuid (
    player_uuid uuid,
    player_full_name text,
    team_name text,
    weight double,
    height double,
    position text,
    PRIMARY KEY (player_uuid)
  )

columnspec:
  - name: player_uuid
    size: fixed(32) # no. of chars of UUID
    population: seq(1..1696)  # 53 active players per team, 32 teams = 1696 players

insert:
  partitions: fixed(1)      # 1 partition per batch
  batchtype: UNLOGGED       # use unlogged batches
  select: fixed(1)/1     # no chance of skipping a row when generating inserts

The following debug output showed that we were over-incrementing the seed

SeedManager.next.index: 341824
SeriesGenerator.Seed.next: 0
SeriesGenerator.Seed.start: 1
SeriesGenerator.Seed.totalCount: 20
SeriesGenerator.Seed.next % totalCount: 0
SeriesGenerator.Seed.start + (next % totalCount): 1
PartitionOperation.ready.seed: org.apache.cassandra.stress.generate.Seed@1
DistributionSequence.nextWithWrap.next: 0
DistributionSequence.nextWithWrap.start: 1
DistributionSequence.nextWithWrap.totalCount: 20
DistributionSequence.nextWithWrap.next % totalCount: 0
DistributionSequence.nextWithWrap.start + (next % totalCount): 1
DistributionSequence.nextWithWrap.next: 1
DistributionSequence.nextWithWrap.start: 1
DistributionSequence.nextWithWrap.totalCount: 20
DistributionSequence.nextWithWrap.next % totalCount: 1
DistributionSequence.nextWithWrap.start + (next % totalCount): 2
Generated uuid: 00000000-0000-0001-0000-000000000002

This patch fixes this issue by calling identityDistribution.next() once instead of twice when generating UUID's