imbajin commented on code in PR #3356:
URL: https://github.com/apache/hugegraph/pull/3356#discussion_r4339724925
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hugegraph-pd/hg-pd-core/src/main/java/org/apache/hugegraph/pd/TaskScheduleService.java:
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@@ -582,6 +630,258 @@ public synchronized Map<Integer, Long>
balancePartitionLeader(boolean immediatel
return results;
}
+ /**
+ * The periodic entry of leader balancing. Calls balancePartitionLeader
only when the leader
+ * count per store has drifted further apart than
pd.balance-leader-max-skew and does not
+ * already match the planner's targets, so a balanced cluster sees no
transfers. Skipped while
+ * a shard group is not Normal, has no recent partition heartbeat or has a
shard that is
+ * neither Leader nor Follower, or while a store that holds a shard is not
active, because the
+ * target distribution would include a replica that cannot take a leader.
The plan uses the
+ * groups checked here; a group keeps its leader when this PD is no longer
the leader, the
+ * group changed, the target or leader store has not reported for
+ * BALANCE_LEADER_REPORT_MAX_AGE, or the target trails the leader by the
time the transfer
+ * would be sent.
+ *
+ * @return shard group id -> the store id its leader was moved to; empty
when skipped
+ */
+ public synchronized Map<Integer, Long> autoBalancePartitionLeader() throws
PDException {
+ // init() does not schedule this with a negative skew, which would
balance every run
+ int maxSkew = pdConfig.getBalanceLeaderMaxSkew();
+ if (!isLeader() || maxSkew < 0) {
+ lastLeaderIndexReports.clear();
+ earlierLeaderIndexReports.clear();
+ return new HashMap<>();
+ }
+
+ List<Metapb.ShardGroup> shardGroups = storeService.getShardGroups();
+ if (shardGroups.isEmpty()) {
+ return new HashMap<>();
+ }
+
+ List<Metapb.Store> stores = storeService.getActiveStores();
Review Comment:
⚠️ Important: `getActiveStores()` reads TTL-backed snapshots. When an online
Store changes to `Exiting`, `StoreNodeService.updateStore()` leaves its TTL
entry in place and the Exiting heartbeat path does not refresh it;
`storeTurnoff()` can rebuild shard membership from that same list, and
`reallocShards()` can add the Exiting Store back as a shard. Once that group is
Normal and the shard is a Follower, this periodic path can select it and move a
leader back to a Store being drained. Please exclude Stores whose current
persisted state is `Exiting` from periodic targets and recheck that state
immediately before dispatch.
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