somandal commented on code in PR #15617:
URL: https://github.com/apache/pinot/pull/15617#discussion_r2055075416
##########
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:
This is actually picked up from `StrictRealtimeSegmentAssignment` which has
this optimization to reduce the overhead of computing the partitionId in case
it has to be fetched from SegmentZkMetadata. Decided to add it here as well,
since otherwise that optimization will essentially be undone. I thought of
exposing it from `StrictRealtimeSegmentAssignment` as well, but it would
require an interface change so decided against it 😅
Reference code:
https://github.com/apache/pinot/blob/9f030bb0f20de69595156c18188946b2d2876e1c/pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/assignment/segment/StrictRealtimeSegmentAssignment.java#L69
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