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Nitro database snapshots

Nitro stores the chain state and data in a database in the local filesystem. When starting Nitro for the first time, it will initialize an empty database by default and start processing transactions from Genesis. It takes a long time for the node to sync from Genesis, so starting from a database snapshot is advisable instead. Moreover, for the Arb1 chain, you must start from a snapshot because Nitro cannot process transactions from the Classic Arbitrum node.

Supply the snapshot URL to Nitro​

There are multiple ways to supply Nitro with the database snapshot. The most straightforward way is to provide the configuration, so Nitro downloads the snapshot by itself. It is also possible to download the database manually and supply it to Nitro.

Downloading the latest snapshot​

Nitro has a CLI configuration for downloading the latest snapshot from a remote server. Set the flag --init.latest to either archive, pruned, or genesis, and Nitro will download the preferred snapshot. You may also change the --init.latest-base flag to set the base URL when searching for the latest snapshot.

How it works​

When searching for the latest snapshot, Nitro uses the chain name provided in --chain.name. Make sure to set it correctly; otherwise, Nitro might be unable to find the snapshot. Nitro will look for a remote file in <latest-base>/<chain-name>/latest-<kind>.txt, where <kind> is the option supplied to --init.latest. This file should contain either the path or the full URL to the snapshot; if it only contains the path, Nitro will use the <latest-base> as the base URL.

After finding the latest snapshot URL, Nitro will download the archive and temporarily store it in the directory specified in --init.download-path. Nitro looks for a SHA256 checksum on the remote server and verifies the checksum of the snapshot after finishing the download. (It is possible to disable this feature by setting --init.validate-checksum to false.)

The snapshot can be a single archive file or a series of parts. Nitro first tries to download the snapshot as a single archive. In this case, Nitro will look for a checksum file in <archive-url>.sha256. If the remote server returns not found (404 status code), Nitro will proceed to download the snapshot in parts. When downloading in parts, Nitro will look for a manifest file in <archive-url>.manifest.txt containing each part's name and checksum. In this case, Nitro will download each part in the manifest file and concatenate them into a single archive.

Finally, Nitro decompresses and extracts the snapshot archive, placing it in the database directory. Nitro will delete the archive after extracting it, so if you need to set up multiple nodes with the same snapshot, consider downloading it manually, as explained below.

Downloading the snapshot from a URL​

Instead of letting Nitro search for the latest snapshot, you can provide a specific URL to download by setting the flag --init.url with the snapshot URL. If the URL points to a remote server, it should start with the https:// protocol definition. Given the URL, Nitro will download the snapshot as described in the "Downloading the Latest Snapshot" section.

Nitro also supports importing files from the local file system. In this case, you should provide the file path to --init.url starting with the prefix file:// followed by the file path. Beware that when running Nitro inside a Docker container, you must mount a volume containing the provided snapshot using the docker flag -v (see Docker documentation). Otherwise, the Nitro container running inside Docker won’t be able to find the snapshot in your local filesystem.

Downloading the snapshot manually​

It is possible to download the snapshot manually and supply the archive instead of having Nitro download it.

The first step is downloading the snapshot. The command below illustrates how to do that on the command line using wget. The -c flag tells the wget to continue the download from where it left off, which is helpful because snapshots can be huge files, and the download can fail mid-way. The -P flag tells wget to place the snapshot on the temporary dir.

wget -c -P /tmp "$SNAPSHOT_URL"

After downloading the snapshot, make sure to verify whether the checksum matches the one provided by the remote server. To fetch the checksum, you may run the command below.

wget -q -O - "$SNAPSHOT_URL".sha256

Once you know the expected snapshot checksum, run the command below to compute the checksum of the downloaded snapshot. Then, compare both and see if they are the same. If they are not the same, consider redownloading the snapshot. You must provide a valid snapshot to Nitro; otherwise, it won’t work properly.

sha256sum $PATH_TO_SNAPSHOT

Finally, you can provide a path to the downloaded snapshot archive to Nitro using the --init.url flag, as described in the "Download the Snapshot from a URL" section.

Downloading snapshot parts​

If the snapshot is divided into parts, you should first download the manifest file in <snapshot-url>.manifest.txt. This manifest contains the names and checksums of each part. For instance, the snippet below shows how the manifest file should look. You may use the commands described previously to download each part of the snapshot and verify their checksums.

a938e029605b81e03cd4b9a916c52d96d74c985ac264e2f298b90495c619af74  archive.tar.part0
9e095ce82e70fa62bb6e7b4421e7f2c04b2cd9e21d2bc62cbbaaeb877408357b  archive.tar.part1
e92172d6eaf770a76c7477e6768f742fc51555a5050de606bd0f837e59c7a61d  archive.tar.part2
d1b6fb9aeeb23903cdbb2a7cca8e6909bff4ee8e51c8a5acac2a142b3e3a5437  archive.tar.part3
f37e4552453202f2044e58b307bab7e466205bd280426abbc84f8646c6430cfa  archive.tar.part4
972c5f513faca6ac4fadd22c70bea97707c6d38e9a646432bc311f0ca10497ed  archive.tar.part5

After downloading all the parts and verifying their checksums, you may use the command below to join them into a single archive.

cat archive.tar.part* > archive.tar

Extracting the snapshot manually​

It is also possible to extract the snapshot archive and place the files manually. First, you need to download the snapshot archive as described in "Manually Downloading the Snapshot". Then, create the directory where Nitro will look for its database. By default, Nitro stores the database on $HOME/.arbitrum/$CHAIN/nitro. Move the archive to this directory and extract it. The commands below exemplify this process for the Arbitrum Sepolia chain.

export CHAIN=sepolia-rollup
export ARCHIVE_PATH=/tmp/archive.tar.gz
mkdir -p $HOME/.arbitrum/$CHAIN/nitro
cd $HOME/.arbitrum/$CHAIN/nitro
tar zxfv $ARCHIVE_PATH

You should see the following subdirectories in this directory after extracting the archive.

arbitrumdata
l2chaindata
nodes

Creating a snapshot​

To generate a snapshot for the Nitro database, you first need to stop the process gracefully. You must not generate the snapshot while Nitro runs because the database might be in an intermediary state. Nitro should print logs like the ones described below when stopping.

^CINFO [08-22|18:10:55.015] shutting down because of sigint
INFO [08-22|18:10:55.016] delayed sequencer: context done          err="context canceled"
INFO [08-22|18:10:55.016] rpc response                             method=eth_getBlockByNumber logId=123 err="context canceled" result=null attempt=0 args="[\"0x405661\", false]"
INFO [08-22|18:10:55.293] Writing cached state to disk             block=39988 hash=8bebf3..939ab2 root=4f7a22..00c334
INFO [08-22|18:10:55.297] Persisted trie from memory database      nodes=643 size=156.31KiB time=3.673459ms gcnodes=329 gcsize=102.61KiB gctime="248.708µs" livenodes=2448 livesize=806.00KiB
INFO [08-22|18:10:55.297] Writing cached state to disk             block=39987 hash=ddcd60..fe0fc3 root=d6973e..7b9265
INFO [08-22|18:10:55.298] Persisted trie from memory database      nodes=34  size=11.19KiB  time="283.875µs" gcnodes=0   gcsize=0.00B     gctime=0s          livenodes=2414 livesize=794.81KiB
INFO [08-22|18:10:55.298] Writing cached state to disk             block=39861 hash=2a9dd3..f00ff0 root=139d5a..d6bf21
INFO [08-22|18:10:55.298] Persisted trie from memory database      nodes=73  size=24.88KiB  time="502.916µs" gcnodes=0   gcsize=0.00B     gctime=0s          livenodes=2341 livesize=769.93KiB
INFO [08-22|18:10:55.299] Writing cached state to disk             block=39861 hash=2a9dd3..f00ff0 root=139d5a..d6bf21
INFO [08-22|18:10:55.299] Persisted trie from memory database      nodes=0   size=0.00B     time="1.417µs"   gcnodes=0   gcsize=0.00B     gctime=0s          livenodes=2341 livesize=769.93KiB
INFO [08-22|18:10:55.299] Writing snapshot state to disk           root=bd18ce..3b0763
INFO [08-22|18:10:55.299] Persisted trie from memory database      nodes=0   size=0.00B     time="1.125µs"   gcnodes=0   gcsize=0.00B     gctime=0s          livenodes=2341 livesize=769.93KiB
INFO [08-22|18:10:55.304] Blockchain stopped

After nitro stops, go to the database directory and generate an archive file for the directories arbitrumdata, l2chaindata, and nodes. By default, the database directory for nitro is $HOME/.arbitrum/$CHAIN/nitro. The commands below exemplify how to generate the snapshot for Nitro.

export CHAIN=sepolia-rollup
export ARCHIVE_PATH=/tmp/archive.tar.gz
cd $HOME/.arbitrum/$CHAIN/nitro
tar zcfv $ARCHIVE_PATH arbitrumdata l2chaindata nodes

This command purposely omits the wasm directory from the snapshot archive. The wasm contains native-code executables, so it might be a security concern for users downloading the snapshot. If the user downloading the snapshot trusts you, or if you are storing it for your own use, you may include the wasm directory in it.

Optional: divide it into parts​

It is possible to divide the snapshot into smaller parts to facilitate its download. This is particularly useful for archive snapshots of heavily used chains, such as arb1. These kinds of snapshots can reach terabytes, so dividing them into smaller parts is helpful. The snippet below illustrates how to divide the snapshot into parts using the split command. The -b argument tells the split to divide the snapshot into 100 GB parts. The -d argument tells split to enumerate the parts using a numeric suffix instead of an alphabetic one.

split -b 100g -d archive.tar.gz archive.tar.gz.part

After dividing it into parts, you should generate the manifest file containing the parts' names and checksums. Nitro will use these files to know how many parts there are and to validate their checksum. The command below exemplifies how to do that.