[Watch] Make watch ID unique per member #21069
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[APPROVALNOTIFIER] This PR is NOT APPROVED This pull-request has been approved by: henrybear327 The full list of commands accepted by this bot can be found here. DetailsNeeds approval from an approver in each of these files:Approvers can indicate their approval by writing |
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@serathius Is there a reason that we should keep the tracking of watchID per stream? This PR doesn't address the case where the user can allocate the same watchID across different stream now. |
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... and 21 files with indirect coverage changes @@ Coverage Diff @@
## main #21069 +/- ##
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+ Coverage 68.44% 68.57% +0.12%
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Lines 35281 35293 +12
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henrybear327
changed the title
server/storage/mvcc/watcher.go
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| // ensure that the nextWatchID check is done in a critical section | ||
| nextWatchIDMutex.Lock() | ||
| for ws.watchers[WatchID(nextWatchID)] != nil { | ||
| nextWatchID++ | ||
| } | ||
| id = ws.nextID | ||
| ws.nextID++ | ||
| id = WatchID(nextWatchID) | ||
| nextWatchID++ | ||
| nextWatchIDMutex.Unlock() |
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The logic is problematic. The nextWatchID is global, but ws.watchers is local to each watchStream. It can't guarantee unique watchID across all watch streams.
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also let alone multiple etcd servers may have same watch IDs
This change makes watch IDs unique per etcd member rather than per stream, which improves debugging by allowing storage to identify clients by watch IDs across connections. The auto-assignment logic now uses a global atomic counter while still checking for conflicts with user-specified IDs on the same stream, avoiding allocating IDs that have been occupied by user requests. Continuation of the work etcd-io#20282. Signed-off-by: Marek Siarkowicz <[email protected]> Signed-off-by: Chun-Hung Tseng <[email protected]>
The previous implementation checked ws.watchers (per-stream) against the global nextWatchID counter, which could not guarantee unique watch IDs across all streams on a member. Bug scenario: - Stream A: User specifies ID=5 → added to ws_A.watchers[5] - Stream B: Auto-assign when counter=5 → checks ws_B.watchers[5] (nil) - Result: Both streams have ID=5, violating per-member uniqueness Fix: Add a global registry (assignedWatchIDs) with reference counting that tracks all watch IDs across all streams. The auto-assignment loop now checks this global registry instead of the per-stream map. Reference counting is needed because user-specified IDs can be duplicated across streams (for backward compatibility), so we only mark an ID as free when no stream is using it. Signed-off-by: Chun-Hung Tseng <[email protected]>
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This change makes watch IDs unique per etcd member rather than per
stream, which improves debugging by allowing storage to identify
clients by watch IDs across connections.
The auto-assignment logic now uses a global atomic counter while
still checking for conflicts with user-specified IDs on the same
stream, avoiding allocating IDs that have
been occupied by user requests.
Continuation of the work #20282.
Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.