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node-manatee

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This repository is part of the Joyent Manta project. For contribution guidelines, issues, and general documentation, visit the main Manta project page.

Overview

This is the client for Manatee. Consumers can use this client to determine the current Manatee shard topology. For background on Manatee itself, look here.

Note this client does not provide you with a handle to an actual PostgreSQL connection. It simply returns the topology of the shard. You will need to manage the PostgreSQL connections yourself.

Example

var manatee = require('node-manatee');

var client = manatee.createClient({
    // Path to the shard's Zookeeper path.
   "path": "/manatee/1",
    // node-zkplus config.
   "zk": {
       "connStr": "172.27.10.97:2181,172.27.10.90:2181,172.27.10.101:2181",
       "opts" {
           "sessionTimeout": 60000,
           "spinDelay": 1000,
           "retries": 2
       }
   }
});
client.once('ready', function () {
    console.log('manatee client ready');
});

client.on('topology', function (urls) {
    console.log({urls: urls}, 'topology changed');
    // insert code here to manage the PG connections.
});

client.on('error', function (err) {
    console.error({err: err}, 'got client error');
});

Configuration

The client config is a JSON object which takes the following parameters.

• path, which is the Zookeeper path of the specific shard. This should be identical to the shardPath parameter in the Manatee server's sitter.json config.
• zk, which is the node-zookeeper-client configuration object.
• An optional log object, which is a bunyan logger.

API

The client emits ready, topology, and error events to consumers.

ready

The ready event is emitted once, when the client has been successfully initialized.

topology

The topology event is emitted everytime there is a possible change in the Shard topology. It emits an ordered array of urls like so:

['tcp://postgres@10.0.0.0:5432', 'tcp://postgres@10.0.0.1:5432', 'tcp://postgres@10.0.0.2:5432']

Where the first element is the primary, the second element the sync, and the third and any additional elements asyncs. Only the primary can be used for writes. If you want strongly consistent data, then only use the primary for reads as well. Otherwise, all 3 nodes can be used for reads, but data on the sync[1] and async will be slightly out of date compared to the primary.

[1] Synchronous replication only ensures that the transaction logs(xlog) are persisted to the standby from the primary when a write request is complete. This doesn't mean the xlog has been processed by the standby. Thus the data from the request will not be immediately available on the standby until it has processed the xlogs from the request a short time later.

error

error is emitted when there is an unrecoverable error with the client. Consumers should reconnect on error events.

Testing

To run the tests you must have access to a running zookeeper cluster. By default the tests look for one running on localhost (127.0.0.1). To point the tests at another endpoint, export the ZK_CONN_STR environment variable with a connection string that represents the set of hosts that can be communicated with. For example:

• export ZK_CONN_STR="127.0.0.1:2181"
• export ZK_CONN_STR="10.99.99.80:2181,10.99.99.81:2181,10.99.99.82:2181"

Then to run the tests:

npm install
./node_modules/.bin/nodeunit ./test/client.test.js