CASSANALYTICS-150 Change commit log mode for CDC tests

[skoppu22]

CDC tests setup in Cassandra analytics is using commit log disk access mode DIRECT. This is causing CI builds running on containers to fail with OOM, as unable to acquire sufficient DIRECT memory on memory constrained containers. Changing commit log mode to mmap works, and this aligns with Cassandra default commit log mode logic (see resolveCommitLogWriteDiskAccessMode in Cassandra)

[skoppu22]

Circle CI run here: https://app.circleci.com/pipelines/github/skoppu22/cassandra-analytics/97/workflows/10a2d885-36fa-4702-931f-1c12be8e837a

[arjunashok]

The git-commit message seems to suggest this is only for tests. I’m wondering if it is only for tests, can we not switch/override it in the test implementation?

Do we intend to switch the default commit log mode?

Also, seems like Cassandra’s default is DiskAccessMode.legacy.
https://github.com/apache/cassandra/blob/addec0ef7ab4c9c023ae8f60c6af565c520368ff/src/java/org/apache/cassandra/config/Config.java#L430

[yifan-c]

+1. waiting for CI results

[yifan-c]

The git-commit message seems to suggest this is only for tests. I’m wondering if it is only for tests, can we not switch/override it in the test implementation?

Do we intend to switch the default commit log mode?

Also, seems like Cassandra’s default is DiskAccessMode.legacy. https://github.com/apache/cassandra/blob/addec0ef7ab4c9c023ae8f60c6af565c520368ff/src/java/org/apache/cassandra/config/Config.java#L430

The code is for testing only. It is to generate the commit logs to test CDC function.

[frankgh]

+1 looks good to me

[skoppu22]

The git-commit message seems to suggest this is only for tests. I’m wondering if it is only for tests, can we not switch/override it in the test implementation?

Do we intend to switch the default commit log mode?

Also, seems like Cassandra’s default is DiskAccessMode.legacy. https://github.com/apache/cassandra/blob/addec0ef7ab4c9c023ae8f60c6af565c520368ff/src/java/org/apache/cassandra/config/Config.java#L430

The modified code gets invoked only in test path using reflection. Cassandra determines commit log mode as below:

 Resolution logic (resolveCommitLogWriteDiskAccessMode in DatabaseDescriptor.class)

 ┌─────────────────┬─────────────────────────┬─────────────────────────────────────┬───────────────────┐
 │ Configured mode │ Compression/Encryption? │             Linux SSD?              │  Effective mode   │
 ├─────────────────┼─────────────────────────┼─────────────────────────────────────┼───────────────────┤
 │ legacy          │ No                      │ (irrelevant)                        │ mmap              │
 ├─────────────────┼─────────────────────────┼─────────────────────────────────────┼───────────────────┤
 │ legacy          │ Yes                     │ (irrelevant)                        │ standard          │
 ├─────────────────┼─────────────────────────┼─────────────────────────────────────┼───────────────────┤
 │ auto            │ No                      │ Yes (block size > 0 + ssd strategy) │ direct            │
 ├─────────────────┼─────────────────────────┼─────────────────────────────────────┼───────────────────┤
 │ auto            │ No                      │ No                                  │ legacy → mmap     │
 ├─────────────────┼─────────────────────────┼─────────────────────────────────────┼───────────────────┤
 │ auto            │ Yes                     │ (irrelevant)                        │ legacy → standard │
 └─────────────────┴─────────────────────────┴─────────────────────────────────────┴───────────────────┘

[skoppu22]

@yifan-c this PR already got 2 approvals. can you merge it please?