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Fast Data Loading

There are two different tools that can be used for fast data loading:

  • dgraph live runs the Dgraph Live Loader
  • dgraph bulk runs the Dgraph Bulk Loader
Note Both tools only accept RDF N-Quad/Triple data or JSON in plain or gzipped format. Data in other formats must be converted.

Live Loader

Dgraph Live Loader (run with dgraph live) is a small helper program which reads RDF N-Quads from a gzipped file, batches them up, creates mutations (using the go client) and shoots off to Dgraph.

Dgraph Live Loader correctly handles assigning unique IDs to blank nodes across multiple files, and can optionally persist them to disk to save memory, in case the loader was re-run.

Note Dgraph Live Loader can optionally write the xid->uid mapping to a directory specified using the --xidmap flag, which can reused given that live loader completed successfully in the previous run.
$ dgraph live --help # To see the available flags.

# Read RDFs or JSON from the passed file, and send them to Dgraph on localhost:9080.
$ dgraph live -f <path-to-gzipped-RDF-or-JSON-file>

# Read multiple RDFs or JSON from the passed path, and send them to Dgraph on localhost:9080.
$ dgraph live -f <./path-to-gzipped-RDF-or-JSON-files>

# Read multiple files strictly by name.
$ dgraph live -f <file1.rdf, file2.rdf>

# Use compressed gRPC connections to and from Dgraph.
$ dgraph live -C -f <path-to-gzipped-RDF-or-JSON-file>

# Read RDFs and a schema file and send to Dgraph running at given address.
$ dgraph live -f <path-to-gzipped-RDf-or-JSON-file> -s <path-to-schema-file> -a <dgraph-alpha-address:grpc_port> -z <dgraph-zero-address:grpc_port>

Encrypted imports via Live Loader (Enterprise Feature)

A new flag --encryption_key_file is added to the Live Loader. This option is required to decrypt the encrypted export data and schema files. Once the export files are decrypted, the Live Loader streams the data to a live Alpha instance. Alternatively, starting with v20.07.0, the vault_* options can be used to decrypt the encrypted export and schema files.

Note If the live Alpha instance has encryption turned on, the p directory will be encrypted. Otherwise, the p directory is unencrypted.

Encrypted RDF/JSON file and schema via Live Loader

dgraph live -f <path-to-encrypted-gzipped-RDF-or-JSON-file> -s <path-to-encrypted-schema> --encryption_keyfile <path-to-keyfile-to-decrypt-files>

Other Live Loader options

--new_uids (default: false): Assign new UIDs instead of using the existing UIDs in data files. This is useful to avoid overriding the data in a DB already in operation.

-f, --files: Location of *.rdf(.gz) or *.json(.gz) file(s) to load. It can load multiple files in a given path. If the path is a directory, then all files ending in .rdf, .rdf.gz, .json, and .json.gz will be loaded.

--format: Specify file format (rdf or json) instead of getting it from filenames. This is useful if you need to define a strict format manually.

-b, --batch (default: 1000): Number of N-Quads to send as part of a mutation.

-c, --conc (default: 10): Number of concurrent requests to make to Dgraph. Do not confuse with -C.

-C, --use_compression (default: false): Enable compression for connections to and from the Alpha server.

-a, --alpha (default: localhost:9080): Dgraph Alpha gRPC server address to connect for live loading. This can be a comma-separated list of Alphas addresses in the same cluster to distribute the load, e.g., "alpha:grpc_port,alpha2:grpc_port,alpha3:grpc_port".

-x, --xidmap (default: disabled. Need a path): Store xid to uid mapping to a directory. Dgraph will save all identifiers used in the load for later use in other data ingest operations. The mapping will be saved in the path you provide and you must indicate that same path in the next load. It is recommended to use this flag if you have full control over your identifiers (Blank-nodes). Because the identifier will be mapped to a specific UID.

--vault_* flags specifies the Vault server address, role id, secret id and field that contains the encryption key that can be used to decrypt the encrypted export.

Bulk Loader

Note It’s crucial to tune the bulk loader’s flags to get good performance. See the section below for details.

Dgraph Bulk Loader serves a similar purpose to the Dgraph Live Loader, but can only be used to load data into a new cluster. It cannot be run on an existing Dgraph cluster. Dgraph Bulk Loader is considerably faster than the Dgraph Live Loader and is the recommended way to perform the initial import of large datasets into Dgraph.

Only one or more Dgraph Zeros should be running for bulk loading. Dgraph Alphas will be started later.

Warning Don’t use bulk loader once the Dgraph cluster is up and running. Use it to import your existing data to a new cluster.

You can read some technical details about the bulk loader on the blog.

See Fast Data Loading for more info about the expected N-Quads format.

Reduce shards: Before running the bulk load, you need to decide how many Alpha groups will be running when the cluster starts. The number of Alpha groups will be the same number of reduce shards you set with the --reduce_shards flag. For example, if your cluster will run 3 Alpha with 3 replicas per group, then there is 1 group and --reduce_shards should be set to 1. If your cluster will run 6 Alphas with 3 replicas per group, then there are 2 groups and --reduce_shards should be set to 2.

Map shards: The --map_shards option must be set to at least what’s set for --reduce_shards. A higher number helps the bulk loader evenly distribute predicates between the reduce shards.

$ dgraph bulk -f goldendata.rdf.gz -s goldendata.schema --map_shards=4 --reduce_shards=2 --http localhost:8000 --zero=localhost:5080
{
	"DataFiles": "goldendata.rdf.gz",
	"DataFormat": "",
	"SchemaFile": "goldendata.schema",
	"DgraphsDir": "out",
	"TmpDir": "tmp",
	"NumGoroutines": 4,
	"MapBufSize": 67108864,
	"ExpandEdges": true,
	"SkipMapPhase": false,
	"CleanupTmp": true,
	"NumShufflers": 1,
	"Version": false,
	"StoreXids": false,
	"ZeroAddr": "localhost:5080",
	"HttpAddr": "localhost:8000",
	"IgnoreErrors": false,
	"MapShards": 4,
	"ReduceShards": 2
}
The bulk loader needs to open many files at once. This number depends on the size of the data set loaded, the map file output size, and the level of indexing. 100,000 is adequate for most data set sizes. See `man ulimit` for details of how to change the limit.
Current max open files limit: 1024
MAP 01s rdf_count:176.0 rdf_speed:174.4/sec edge_count:564.0 edge_speed:558.8/sec
MAP 02s rdf_count:399.0 rdf_speed:198.5/sec edge_count:1.291k edge_speed:642.4/sec
MAP 03s rdf_count:666.0 rdf_speed:221.3/sec edge_count:2.164k edge_speed:718.9/sec
MAP 04s rdf_count:952.0 rdf_speed:237.4/sec edge_count:3.014k edge_speed:751.5/sec
MAP 05s rdf_count:1.327k rdf_speed:264.8/sec edge_count:4.243k edge_speed:846.7/sec
MAP 06s rdf_count:1.774k rdf_speed:295.1/sec edge_count:5.720k edge_speed:951.5/sec
MAP 07s rdf_count:2.375k rdf_speed:338.7/sec edge_count:7.607k edge_speed:1.085k/sec
MAP 08s rdf_count:3.697k rdf_speed:461.4/sec edge_count:11.89k edge_speed:1.484k/sec
MAP 09s rdf_count:71.98k rdf_speed:7.987k/sec edge_count:225.4k edge_speed:25.01k/sec
MAP 10s rdf_count:354.8k rdf_speed:35.44k/sec edge_count:1.132M edge_speed:113.1k/sec
MAP 11s rdf_count:610.5k rdf_speed:55.39k/sec edge_count:1.985M edge_speed:180.1k/sec
MAP 12s rdf_count:883.9k rdf_speed:73.52k/sec edge_count:2.907M edge_speed:241.8k/sec
MAP 13s rdf_count:1.108M rdf_speed:85.10k/sec edge_count:3.653M edge_speed:280.5k/sec
MAP 14s rdf_count:1.121M rdf_speed:79.93k/sec edge_count:3.695M edge_speed:263.5k/sec
MAP 15s rdf_count:1.121M rdf_speed:74.61k/sec edge_count:3.695M edge_speed:246.0k/sec
REDUCE 16s [1.69%] edge_count:62.61k edge_speed:62.61k/sec plist_count:29.98k plist_speed:29.98k/sec
REDUCE 17s [18.43%] edge_count:681.2k edge_speed:651.7k/sec plist_count:328.1k plist_speed:313.9k/sec
REDUCE 18s [33.28%] edge_count:1.230M edge_speed:601.1k/sec plist_count:678.9k plist_speed:331.8k/sec
REDUCE 19s [45.70%] edge_count:1.689M edge_speed:554.4k/sec plist_count:905.9k plist_speed:297.4k/sec
REDUCE 20s [60.94%] edge_count:2.252M edge_speed:556.5k/sec plist_count:1.278M plist_speed:315.9k/sec
REDUCE 21s [93.21%] edge_count:3.444M edge_speed:681.5k/sec plist_count:1.555M plist_speed:307.7k/sec
REDUCE 22s [100.00%] edge_count:3.695M edge_speed:610.4k/sec plist_count:1.778M plist_speed:293.8k/sec
REDUCE 22s [100.00%] edge_count:3.695M edge_speed:584.4k/sec plist_count:1.778M plist_speed:281.3k/sec
Total: 22s

The output will be generated in the out directory by default. Here’s the bulk load output from the example above:

$ tree ./out
./out
├── 0
│   └── p
│       ├── 000000.vlog
│       ├── 000002.sst
│       └── MANIFEST
└── 1
    └── p
        ├── 000000.vlog
        ├── 000002.sst
        └── MANIFEST

4 directories, 6 files

Because --reduce_shards was set to 2, there are two sets of p directories: one in ./out/0 directory and another in the ./out/1 directory.

Once the output is created, they can be copied to all the servers that will run Dgraph Alphas. Each Dgraph Alpha must have its own copy of the group’s p directory output. Each replica of the first group should have its own copy of ./out/0/p, each replica of the second group should have its own copy of ./out/1/p, and so on.

$ dgraph bulk --help # To see the available flags.

# Read RDFs or JSON from the passed file.
$ dgraph bulk -f <path-to-gzipped-RDF-or-JSON-file> ...

# Read multiple RDFs or JSON from the passed path.
$ dgraph bulk -f <./path-to-gzipped-RDF-or-JSON-files> ...

# Read multiple files strictly by name.
$ dgraph bulk -f <file1.rdf, file2.rdf> ...

Encryption at rest with Bulk Loader (Enterprise Feature)

Even before the Dgraph cluster starts, we can load data using Bulk Loader with the encryption feature turned on. Later we can point the generated p directory to a new Alpha server.

Here’s an example to run Bulk Loader with a key used to write encrypted data:

dgraph bulk --encryption_key_file ./enc_key_file -f data.json.gz -s data.schema --map_shards=1 --reduce_shards=1 --http localhost:8000 --zero=localhost:5080

Alternatively, starting with v20.07.0, the vault_* options can be used to decrypt the encrypted export.

Encrypting imports via Bulk Loader (Enterprise Feature)

The Bulk Loader’s encryption_key_file option was previously used to encrypt the output p directory. This same option will also be used to decrypt the encrypted export data and schema files.

Another option, --encrypted, indicates whether the input rdf/json data and schema files are encrypted or not. With this switch, we support the use case of migrating data from unencrypted exports to encrypted import.

So, with the above two options we have 4 cases:

  1. --encrypted=true and no encryption_key_file.

Error: If the input is encrypted, a key file must be provided.

  1. --encrypted=true and encryption_key_file=`path to key.

Input is encrypted and output p dir is encrypted as well.

  1. --encrypted=false and no encryption_key_file.

Input is not encrypted and the output p dir is also not encrypted.

  1. --encrypted=false and encryption_key_file=path to key.

Input is not encrypted but the output is encrypted. (This is the migration use case mentioned above).

Alternatively, starting with v20.07.0, the vault_* options can be used instead of the --encryption_key_file option above to achieve the same effect except that the keys are sitting in a Vault server.

Other Bulk Loader options

--new_uids (default: false): Assign new UIDs instead of using the existing UIDs in data files. This is useful to avoid overriding the data in a DB already in operation.

-f, --files: Location of *.rdf(.gz) or *.json(.gz) file(s) to load. It can load multiple files in a given path. If the path is a directory, then all files ending in .rdf, .rdf.gz, .json, and .json.gz will be loaded.

--format: Specify file format (rdf or json) instead of getting it from filenames. This is useful if you need to define a strict format manually.

--store_xids: Generate a xid edge for each node. It will store the XIDs (The identifier / Blank-nodes) in an attribute named xid in the entity itself. It is useful if you gonna use External IDs.

--xidmap (default: disabled. Need a path): Store xid to uid mapping to a directory. Dgraph will save all identifiers used in the load for later use in other data ingest operations. The mapping will be saved in the path you provide and you must indicate that same path in the next load. It is recommended to use this flag if you have full control over your identifiers (Blank-nodes). Because the identifier will be mapped to a specific UID.

--vault_* flags specifies the Vault server address, role id, secret id and field that contains the encryption key that can be used to decrypt the encrypted export.

Tuning & monitoring

Performance Tuning

Tip We highly recommend disabling swap space when running Bulk Loader. It is better to fix the parameters to decrease memory usage, than to have swapping grind the loader down to a halt.

Flags can be used to control the behaviour and performance characteristics of the bulk loader. You can see the full list by running dgraph bulk --help. In particular, the flags should be tuned so that the bulk loader doesn’t use more memory than is available as RAM. If it starts swapping, it will become incredibly slow.

In the map phase, tweaking the following flags can reduce memory usage:

  • The --num_go_routines flag controls the number of worker threads. Lowering reduces memory consumption.

  • The --mapoutput_mb flag controls the size of the map output files. Lowering reduces memory consumption.

For bigger datasets and machines with many cores, gzip decoding can be a bottleneck during the map phase. Performance improvements can be obtained by first splitting the RDFs up into many .rdf.gz files (e.g. 256MB each). This has a negligible impact on memory usage.

The reduce phase is less memory heavy than the map phase, although can still use a lot. Some flags may be increased to improve performance, but only if you have large amounts of RAM:

  • The --reduce_shards flag controls the number of resultant Dgraph alpha instances. Increasing this increases memory consumption, but in exchange allows for higher CPU utilization.

  • The --map_shards flag controls the number of separate map output shards. Increasing this increases memory consumption but balances the resultant Dgraph alpha instances more evenly.

  • The --shufflers controls the level of parallelism in the shuffle/reduce stage. Increasing this increases memory consumption.