Name of a disk snapshot.

The snapshot itself might not yet exist on disk.

Number of snapshots to be stored on disk. See the SnapshotPolicy documentation for more information.

Read an extended ledger state from disk

Write an extended ledger state to disk

The snapshots that are periodically created are temporary, they will be deleted when trimming or if they fail to deserialize.

The path within the LedgerDB's filesystem to the file that contains the snapshot's serialized ledger state

The path within the LedgerDB's filesystem to the snapshot's directory

Management of snapshots for the different LedgerDB backends.

The LedgerDB V1 takes snapshots in ReadLocked m, hence the two different m and n monad types.

Delete snapshot from disk

List on-disk snapshots, highest number first.

Trim the number of on disk snapshots so that at most onDiskNumSnapshots snapshots are stored on disk. The oldest snapshots are deleted.

The deleted snapshots are returned.

Load a snapshot metadata JSON file.

• Fails with MetadataFileDoesNotExist when the file doesn't exist;
• Fails with MetadataInvalid when the contents of the file cannot be deserialised correctly

Write a snapshot metadata JSON file.

Snapshots policy

We only write ledger states that are older than k blocks to disk (that is, snapshots that are guaranteed valid). The on-disk policy determines how often we write to disk and how many checkpoints we keep.

Range from which the randomised snapshot delay will be taken. The randomly chosen duration will be at least minimumDelay and at most maximumDelay.

Determines when/how often we take ledger snapshots.

We only write snapshots for ledger states that are immutable. Concretely, for every slot s out of

sfaOffset, sfaOffset + sfaInterval, sfaOffset + 2 * sfaInterval, sfaOffset + 3 * sfaInterval, ...

we write a snapshot for the most recent immutable ledger state before s. This way, nodes with the same sfaInterval/sfaOffset configuration create snapshots for precisely the same slots.

For example, on Cardano mainnet, where k=2160 and f=1/20, setting sfaInterval = 10*k/f = 432000 (one epoch) and sfaOffset = 0 will cause the node to create snapshots for the last block in every Shelley epoch. By setting sfaOffset to eg 5*k/f (half an epoch), snapshots are created just before the midway point in each epoch.

Additionally, there is an (optional, opt-out) rate limit (useful while bulk-syncing). When set to a given duration, we will skip writing a snapshot if less time than the given duration has passed since we finished writing the previous snapshot (if any).

To avoid skipping a snapshot write when caught-up, it is advisable to set sfaRateLimit to something significantly smaller than the wall-clock duration of sfaInterval.

Default on-disk policy suitable to use with cardano-node

The Cardano mainnet epoch length in slots, used as the reference for the Mithril snapshot compatibility check in sanityCheckSnapshotPolicyArgs. Mithril requires a ledger snapshot at each epoch boundary; for snapshots to land on every epoch boundary, sfaInterval must divide this value evenly.

Check a SnapshotPolicyArgs for suspicious configurations and return a (possibly empty) list of SanityCheckIssues describing any problems found.

Only Override values are checked — UseDefault values are known-good and are never flagged. Checks that are specific to SnapshotFrequency are skipped entirely when spaFrequency is DisableSnapshots.

Type-safe flag to regulate the checksum policy of the ledger state snapshots.

These patterns are exposed to cardano-node and will be passed as part of SnapshotPolicy.

Type-safe flag to regulate the checksum policy of the ledger state snapshots.

These patterns are exposed to cardano-node and will be passed as part of SnapshotPolicy.

Type-safe boolean flags with type level tags

It is recommended to create pattern synonyms for the true and false values.

See DiskSnapshotChecksum for an example.

To remain backwards compatible with existing snapshots stored on disk, we must accept the old format as well as the new format.

The old format:

• The tip: WithOrigin (RealPoint blk)
• The chain length: Word64
• The ledger state: l

The new format is described by snapshotEncodingVersion1.

This decoder will accept and ignore them. The encoder (encodeSnapshot) will no longer encode them.

Testing only! Destroy all snapshots in the DB.

Encoder to be used in combination with decodeSnapshotBackwardsCompatible.