dosubot[bot] commented on issue #2605:
URL:
https://github.com/apache/incubator-hugegraph/issues/2605#issuecomment-2256295579
<!-- Answer -->
The Placement Driver (PD) assigns a partition ID when creating a graph in
HugeGraph by calculating the partition ID based on a hash code derived from the
key. The process involves the following steps:
1. **Calculate the Hash Code**: The hash code is calculated using the key.
2. **Determine Partition Size**: The partition size is determined by
dividing a maximum value (`PartitionUtils.MAX_VALUE`) by the number of
partitions in the graph.
3. **Calculate Partition ID**: The partition ID is calculated by dividing
the hash code by the partition size.
4. **Determine Start and End Keys**: The start and end keys for the
partition are calculated based on the partition size and partition ID.
5. **Check and Create Partition**: If the partition does not already exist,
it is created and assigned a store.
Here is the relevant code snippet:
```java
private Metapb.Partition newPartition(String graphName, long code) throws
PDException {
Metapb.Graph graph = partitionMeta.getAndCreateGraph(graphName);
int partitionSize = PartitionUtils.MAX_VALUE / graph.getPartitionCount();
if (PartitionUtils.MAX_VALUE % graph.getPartitionCount() != 0) {
// There is a remainder, and the partition is inexhaustible
partitionSize++;
}
int partitionId = (int) (code / partitionSize);
long startKey = (long) partitionSize * partitionId;
long endKey = (long) partitionSize * (partitionId + 1);
// Check Local
Metapb.Partition partition = partitionMeta.getPartitionById(graphName,
partitionId);
if (partition == null) {
storeService.allocShards(null, partitionId);
// Assign a store
partition = Metapb.Partition.newBuilder()
.setId(partitionId)
.setVersion(0)
.setState(Metapb.PartitionState.PState_Normal)
.setStartKey(startKey)
.setEndKey(endKey)
.setGraphName(graphName)
.build();
log.info("Create newPartition {}", partition);
}
partitionMeta.updatePartition(partition);
return partition;
}
```
This code ensures that each partition is uniquely identified and
appropriately assigned within the graph
<sup>[[1]](https://github.com/apache/incubator-hugegraph/blob/master/hugegraph-pd/hg-pd-core/src/main/java/org/apache/hugegraph/pd/PartitionService.java)</sup><sup>[[2]](https://github.com/apache/incubator-hugegraph/blob/master/hugegraph-store/hg-store-core/src/main/java/org/apache/hugegraph/store/pd/DefaultPdProvider.java)</sup>.
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