Cannot run relayer commands concurrently

[romac]

Crate

relayer, relayer-cli, tendermint-light-client

Problem Definition

If one attempts to run two relayer commands concurrently (eg. tx raw packet-send while the relayer is running), they will be greeted with an error like:

error: client create failed: tx error: Light client error: IO error: could not acquire lock on "data/DEEB0AB3F2D7BEC0B8C9FF1532715635314F54D5/db": Os { code: 35, kind: WouldBlock, message: "Resource temporarily unavailable" }

This happens because each processes will instantiate a chain runtime which in turn will instantiate a light client, and both light clients will attempt to open the same sled database.

In turns out that sled does not allow multiple processes to have the database file open at once, hence the error above.

Proposal

Implement a new instance of the LightStore trait backed by a database which supports concurrent use across processes (eg. SQLite, RocksDB).

Alternatively, standalone commands (ie. tx commands) could use an in-memory light store, thus reserving the on-disk on for the main relayer loop (start command). This has performance implication for those commands as they will start from an empty light store and should thus be evaluated carefully.

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For Admin Use

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