jaegertracing/jaeger

[storage] limitations of Cassandra search on LIMIT and complex queries

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#166 opened on May 16, 2017

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Description

When querying for traces using serviceName, operationName and a tag with the default LIMIT of 20, some results might be omitted.

This is because of this logic which does the following:

  1. Retrieve all traceIDs matching the operation name
  2. Retrieve all traceIDs matching tags
  3. Intersect 1 & 2

Because Cassandra doesn't guarantee ordering, this could eliminate results.

I propose that we do the following instead (or in addition to what we do now),

  1. Retrieve all traceIds matching tags
  2. Filter by operation name

The reason for retrieving traceIds matching tags first targets the use case when somebody is searching for a jaeger-debug-id or some other tag with low cardinality, guaranteeing them a result when it exists.

Contributor guide

Research direction
Study the code at https://github.com/jaegertracing/jaeger/blob/b756da12e287f83143425fc6351ef76eb10db4b4/plugin/storage/cassandra/spanstore/reader.go#L260 L276 and modify the intersection logic to prioritize tag based retrieval when a low cardinality tag like 'jaeger debug id' is used.
Tech stack
go
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Go
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70