Allow multiple tablet pools of the same type - #800
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I didn't use table driven tests because I didn't see them used elsewhere and the coverage is only rudimentary, but the tests passed for me and I've deployed this fork into our internal Vitess clusters. In our environments, I have also leveraged the |
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Pull request overview
This PR updates tablet UID generation so multiple tablet pools can share the same (cell, type) without requiring ExternalDatastore, and introduces a compatibility flag (--default_pool_names) to preserve existing tablet UIDs during migrations.
Changes:
- Add
--default_pool_namesoperator flag and helpers for treating certain pool names as “unnamed” during UID generation. - Generate name-aware tablet UIDs for non-default named pools, independent of
ExternalDatastore. - Add unit tests covering UID behavior for default vs non-default pool names and mixed pools in the same (cell, type).
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
| pkg/operator/environment/environment.go | Adds --default_pool_names flag and helpers to control backward-compatible UID generation. |
| pkg/controller/vitessshard/reconcile_tablets.go | Updates UID generation logic to use pool names (except configured defaults) and adjusts pool-name labeling behavior. |
| pkg/controller/vitessshard/reconcile_tablets_test.go | Adds tests validating UID stability for default pool names and uniqueness across multiple pools. |
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| if 0 < len(pool.Name) { | ||
| labels[planetscalev2.TabletPoolNameLabel] = pool.Name | ||
| } |
| // If TabletPools has multiple pools within the same (cell,type) pair, we need to add a pool name to the UID generator. | ||
| if pool.ExternalDatastore != nil && 0 < len(pool.Name) { | ||
| // Pool names listed in --default_pool_names are treated as unnamed to preserve existing tablet UIDs. | ||
| if 0 < len(pool.Name) && !environment.IsDefaultPoolName(pool.Name) { |
| // tabletsForPool returns the tablet specs belonging to the named pool, using | ||
| // the pool-name label that vttabletSpecs stamps on every tablet. |
| func SetDefaultPoolNames(names []string) { | ||
| defaultPoolNames = names | ||
| } |
mattlord
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mattlord
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Thanks, @absolutejam ! ❤️ There are a few things that I think we should try and address before merging (sometimes it can be resolved in a discussion vs code changes).
I think that it's worth guarding against default-pool UID collisions in pkg/controller/vitessshard/reconcile_tablets.go:286. The new --default_pool_names behavior can make two pools in the same (cell,type) both use the legacy unnamed UID path. For example, an unnamed pool plus a default-named pool, or two named pools both listed in --default_pool_names, will generate the same tablet UIDs for the same indexes. That seems like it can make the desired tablet map overwrite one pool with the other, reusing the same pod/PVC/tablet alias identity. I think we should reject or otherwise prevent more than one “legacy UID” pool per (cell,type), and add a regression test for that case.
I think that we should Include the pool name in “same pool” anti-affinity labels in pkg/operator/vttablet/spec.go:67. Named local pools can now represent distinct pools with the same cell/type, but poolLabels() still does not include TabletPoolNameLabel. That means the default anti-affinity that is described as applying to the “same exact pool” still groups separate named pools together. I think we should include the pool name label there when present so scheduling behavior matches the new pool identity model.
We will need to update the API/CRD wording for named local pools
in pkg/apis/planetscale/v2/vitessshard_types.go:147
pkg/apis/planetscale/v2/labels.go:39. The Name field comment still says a pool name requires ExternalDatastore, and the pool-name label comment still says it applies to Vitess-unmanaged keyspaces. Since this PR intentionally supports named local pools, I think we should update those comments and regenerate any CRD descriptions derived from them so users do not think the new configuration is unsupported.
Side note, the DCO is currently failing on the PR. If you click on that failed workflow it will give you precise instructions for how to fix it.
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Thanks for the thoughtful comments @mattlord - I think adding a guard for UID collisions is the right move. I've updated the documentation now and restricted |
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Signed-off-by: James Booth <james@absolutejam.co.uk>
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Removes the external data store requirement for multiple tabletpools.
Also adds
--default_pool_namesflag which can optionally be supplied to keep backwards compatible behaviour for the specified pools.