mdelacruz-avantio opened a new issue, #9280:
URL: https://github.com/apache/devlake/issues/9280

   ### Search before asking
   - [x] I had searched in the issues and found no similar issues.
   
   ### What happened
   `batchFetchDeployments` in 
`backend/plugins/dora/tasks/change_lead_time_calculator.go` resolves merge 
commits to deployments in two phases. The second phase joins 
`cicd_deployment_commits` with `commits_diffs`, loads every joined row into a 
slice of full `CicdDeploymentCommit` structs with `db.All`, and only then keeps 
the first row per merge commit in Go.
   
   Memory therefore grows with the size of the join, not with the number of 
merge commits. The join has one row per commit between a production deployment 
and its previous successful one, for every merge commit in that range. On a 
project where deployments are far apart in commit history, or where a 
deployment job records a commit from a second repository with a long history, 
the join becomes very large.
   
   On our instance the query returns about 936,000 rows for 14,088 distinct 
merge commits (1,693 production deployment commits). The lake container peaks 
at about 1.7 GiB in this subtask, is OOMKilled at a 2 GiB limit on every 
nightly run, and then crash loops because each restart resumes the same 
pipeline at the same subtask. The row count grows every week.
   
   ### What do you expect to happen
   The memory used by this subtask stays proportional to the number of distinct 
merge commits, as the first phase already does, whatever the size of the 
`commits_diffs` join.
   
   ### How to reproduce
   1. A project with a few hundred production deployment commits where 
consecutive deployments are thousands of commits apart, so `commits_diffs` 
holds many rows per deployment pair.
   2. Run the DORA pipeline and watch the lake container memory during 
`calculateChangeLeadTime`, or count the rows the second phase loads:
   
   ```sql
   SELECT COUNT(*), COUNT(DISTINCT cd.commit_sha)
   FROM cicd_deployment_commits dc
   LEFT JOIN cicd_deployment_commits p ON dc.prev_success_deployment_commit_id 
= p.id
   INNER JOIN commits_diffs cd ON cd.new_commit_sha = dc.commit_sha AND 
cd.old_commit_sha = COALESCE(p.commit_sha, '')
   LEFT JOIN project_mapping pm ON pm.table = 'cicd_scopes' AND pm.row_id = 
dc.cicd_scope_id
   WHERE dc.prev_success_deployment_commit_id <> '' AND dc.environment = 
'PRODUCTION' AND dc.result = 'SUCCESS' AND pm.project_name = '<project>';
   ```
   
   The first number is what the subtask materialises, the second is what it 
keeps.
   
   ### Anything else
   Streaming the second phase with `db.Cursor` and `db.Fetch` into a 
three-column struct and keeping the first row per merge commit, with the same 
joins, filters and ordering, makes the memory independent of the join size. I 
will open a pull request with that change and an e2e case for the first-wins 
tie-break.
   
   Raising the container memory limit and setting `GOMEMLIMIT` is a stopgap 
only, the peak keeps growing with the join.
   
   ### Version
   v1.0.3-beta18. The function is unchanged on `main` at 625e512a4.
   


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