Make write threads for applier configurable#549
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morgo merged 6 commits intoblock:mainfrom Jan 5, 2026
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| TargetDSN string `name:"target-dsn" help:"Where to copy the tables to." default:"spirit:spirit@tcp(127.0.0.1:3306)/dest"` | ||
| TargetChunkTime time.Duration `name:"target-chunk-time" help:"How long each chunk should take to copy" default:"5s"` | ||
| Threads int `name:"threads" help:"How many chunks to copy in parallel" default:"2"` | ||
| WriteThreads int `name:"write-threads" help:"How many concurrent write threads to use per target" default:"2"` |
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would it be apparent when errors pop up that we'd need to tweak the default threads up here?
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It's was not obvious why the tests were failing, but I reduced the concurrency and it worked.
This is similar to scenarios like OOM and CPU load. Programs start performing unreliably.
I tried to consider that it might be something like a race, and thus there's a bug that is fixable. But I don't think that's the case.
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Previously we used 40 write threads regardless. This is going to be a problem when running concurrent tests in CI (the appliers are still experimental, so there aren't that many tests for them yet).
I've changed it to be configurable. This changes the signature of
NewSingleTargetAppliersuch that it can return errors. This is the same asNewShardedApplier.