dosubot[bot] commented on issue #2605:
URL:
https://github.com/apache/incubator-hugegraph/issues/2605#issuecomment-2256401080
<!-- Answer -->
The HugeGraph server retrieves partition information from the Placement
Driver (PD) when creating a new graph by using the `PDClient` class.
Specifically, it uses the `getPartitionByCode` method to find the partition
based on a hash code. If the partition does not exist, it creates a new
partition using the `newPartition` method.
Here is the relevant code:
```java
public KVPair<Metapb.Partition, Metapb.Shard> getPartitionByCode(String
graphName, long code) throws PDException {
if (code < 0 || code >= PartitionUtils.MAX_VALUE) {
throw new PDException(Pdpb.ErrorType.NOT_FOUND_VALUE, "code error");
}
// Find the partition ID based on the code, and if it doesn't find,
create a new partition
KVPair<Metapb.Partition, Metapb.Shard> partShard =
cache.getPartitionByCode(graphName, code);
if (partShard == null) {
synchronized (this) {
if (partShard == null) {
partShard = newPartition(graphName, code);
}
}
}
log.debug("{} Partition get code = {}, partition id = {}, start = {},
end = {}， leader = {}",
graphName, (code), partShard.getKey().getId(),
partShard.getKey().getStartKey(), partShard.getKey().getEndKey(),
partShard.getValue());
return partShard;
}
private KVPair<Metapb.Partition, Metapb.Shard> newPartition(String
graphName, long code) throws PDException {
Metapb.Graph graph = getGraph(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
KVPair<Metapb.Partition, Metapb.Shard> partShard =
cache.getPartitionById(graphName, partitionId);
if (partShard == null) {
storeService.allocShards(null, partitionId);
// Assign a store
Metapb.Partition 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);
partShard = new KVPair<>(partition,
storeService.getLeader(partition, 0));
}
cache.updatePartition(partShard.getKey());
return partShard;
}
```
This code shows how the server calculates the partition hash code, checks if
the partition exists, and creates a new partition if necessary. The `PDClient`
class handles the communication with the PD server, including caching and
updating partition information
<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-pd/hg-pd-client/src/main/java/org/apache/hugegraph/pd/client/PDClient.java)</sup>.
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