Reading the LiteFS event stream

LiteFS provides mechanisms for reading the replication position and current primary status through the FUSE file system mount. However, this involves polling the file system which has overhead and some delay. If you need real-time updates of replication or primary changes, you can also use the LiteFS event stream. The event stream is an HTTP endpoint that sends a newline-delimited JSON stream of events to the client.

Usage

The event stream is accessible at GET /events on your LiteFS node:

$ curl localhost:20202/events
{"type":"init","data":{"isPrimary":true}}
{"type":"tx","db":"db","data":{"txID":"0000000000000027","postApplyChecksum":"83b05248774ce767","pageSize":4096,"commit":2,"timestamp":"2023-09-06T19:12:34.985Z"}}
{"type":"tx","db":"db","data":{"txID":"0000000000000028","postApplyChecksum":"8467267f644a1b66","pageSize":4096,"commit":2,"timestamp":"2023-09-06T19:12:39.586Z"}}

Event Types

`init`

The init event is always the first event published to an event stream. It includes basic information about whether the local node is the primary and, if not, the hostname of the current primary. More fields may be added to this event in the future.

{
    "type": "init",
    "data": {
        "isPrimary": false,
        "hostname": "myPrimaryHost:20202"
    }
}

`tx`

This event is published every time a new transaction is written to LiteFS. This event will fire whether the transaction is performed locally as the primary or if the transaction was received by a replica. The txID field is a hex-formatted transaction ID. The postApplyChecksum is a checksum of the entire database after the transaction has been applied. These two fields form the replication position. The commit field is the size of the database in pages and can be multiplied by the pageSize field to give you the total size of the database file in bytes. The timestamp field is the timestamp of when the transaction was originally written on the primary node. This is not always reliable as clocks can skew between different servers.

{
    "type": "tx",
    "db": "db",
    "data": {
        "txID": "0000000000000027",
        "postApplyChecksum": "83b05248774ce767",
        "pageSize": 4096,
        "commit": 2,
        "timestamp": "2023-09-06T19:12:34.985Z"
    }
}

`primaryChange`

This event shows information about the current primary status. It is delivered whenever the status changes such as when the node becomes primary, loses its primary status, connects to a primary, or loses its connection to the primary.

{
    "type": "primaryChange",
    "data": {
        "isPrimary": false,
        "hostname": "myPrimaryHost:20202"
    }
}

​Usage

​Event Types

​init

​tx

​primaryChange

Usage

Event Types

`init`

`tx`

`primaryChange`