somandal commented on code in PR #15617:
URL: https://github.com/apache/pinot/pull/15617#discussion_r2059080890
##########
pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/rebalance/TableRebalancer.java:
##########
@@ -479,6 +482,16 @@ private RebalanceResult doRebalance(TableConfig
tableConfig, RebalanceConfig reb
externalViewStabilizationTimeoutInMs);
int expectedVersion = currentIdealState.getRecord().getVersion();
+ // Cache segment partition id to avoid ZK reads. Similar behavior as cache
used in StrictReplicaGroupAssignment
+ // NOTE:
+ // 1. This cache is used for table rebalance only, but not segment
assignment. During rebalance, rebalanceTable()
+ // can be invoked multiple times when the ideal state changes during
the rebalance process.
+ // 2. The cache won't be refreshed when an existing segment is replaced
with a segment from a different partition.
+ // Replacing a segment with a segment from a different partition should
not be allowed for upsert table because
+ // it will cause the segment being served by the wrong servers. If this
happens during the table rebalance,
+ // another rebalance might be needed to fix the assignment.
+ Object2IntOpenHashMap<String> segmentPartitionIdMap = new
Object2IntOpenHashMap<>();
Review Comment:
I am not against the idea but want some thoughts from @Jackie-Jiang on this.
That cache is private to `StrictRealtimeSegmentAssignment` and not relevant for
other segment assignments, so definitely don't want to expose an interface to
access that. Other option is to make this public, but I kind of think that
leaks the internal behavior of `StrictRealtimeSegmentAssignment` outside.
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