Function preShardingForHashed

tools/pre-split/pre_split.go:582–622

preShardingForHashed does the pre-sharding work for hashed sharding

(srcC, dstC *mongo.Client, dbName, collName string, shardKey bson.D,
	unique bool, uuid *primitive.Binary, chunkNum int64)

// preShardingForHashed does the pre-sharding work for hashed sharding
func preShardingForHashed(srcC, dstC *mongo.Client, dbName, collName string, shardKey bson.D,
	unique bool, uuid *primitive.Binary, chunkNum int64) error {
	// simple use 'shardCollection' with 'numInitialChunks' option,
	// but only when the hashed index key is the prefix of shard key
	if shardKey[0].Value == "hashed" {
		// run 'enableSharding', it's ok to run multi times
		if SrcV.GTE(Version600) {
			cmd := bson.D{{Key: "enableSharing", Value: dbName}}
			if *dryRun {
				log.Infof("[DRY_RUN] db.adminCommand( %v )", cmd)
			} else {
				res := dstC.Database(DbAdmin).RunCommand(context.Background(), cmd)
				if res.Err() != nil {
					return fmt.Errorf("error enabling sharding for %s: %v", dbName, res.Err())
				}
			}
		}

		// run 'shardCollection'
		// todo: support other options like 'collation'/'timeseries'
		cmd := bson.D{
			{Key: "shardCollection", Value: fmt.Sprintf("%s.%s", dbName, collName)},
			{Key: "key", Value: shardKey},
			{Key: "unique", Value: unique},
			{Key: "numInitialChunks", Value: chunkNum}, // 或者根据你的需求指定一个合适的值
		}
		if *dryRun {
			log.Infof("[DRY_RUN] db.adminCommand( %v )", cmd)
		} else {
			res := dstC.Database(DbAdmin).RunCommand(context.Background(), cmd)
			if res.Err() != nil {
				return fmt.Errorf("error pre-splitting hashed collection %s.%s: %v", dbName, collName, res.Err())
			}
		}
	} else {
		// use preSharingForRange instead
		return preSharingForRange(srcC, dstC, dbName, collName, shardKey, unique, uuid, chunkNum)
	}

	return nil
}

// countChunks count the number of chunks for specified sharded collection, support all db versions
func countChunks(c *mongo.Client, dbName, collName string, uuid *primitive.Binary, dbVersion Version) (int64, error) {