larch
v1.5.0
Published
reservoir sampled logger
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Larch
It's a logging framework. Currently it's main use is to reservoir sample logs and forward them to Logtron. In the long term, it may replace Logtron. It can be used like this:
var Logtron = require('logtron');
var Larch = require('larch');
var LogtronBackend = require('larch/logtron-backend');
var ReservoirBackend = require('larch/reservoir-backend');
var clients = ...
var logtronLogger = Logtron({...});
var logger = Larch({
backends: [ReservoirBackend({
backend: LogtronBackend(logtronLogger),
statsd: clients.statsd,
clusterStatsd: clients.clusterStatsd,
size: 100,
flushInterval: 50
})]
});
logger.bootstrap();
logger.warn('warn string', {meta: 'object'});
Docs
Larch({ backends: Array })
Larch
is a constructor that takes a list of backends.
Generally you want to use the ReservoirBackend
larch.bootstrap()
Remember to call bootstrap()
on larch to start the reservoir.
ReservoirBackend(opts)
ReservoirBackend
takes a set of options including:
backend
; what to write to if we sample the log callstatsd
; where to emit stats.clusterStatsd
; where to emit cluster-wide latency stats.size
; The amount of records that can be logged per intervalflushInterval
; How often we should flush the reservoir
The reservoir will log (1000 / flushInterval
) * size
records per second.
This means by default it will log 2000
records per second.
Using willSample($level, $msg)
The top level Larch object, as well as each backend, has a method willSample
.
This method returns true
if any backend after this backend in the object tree
is interested in taking a log with level $level
. This can be used to avoid
allocating space for large meta objects, like so:
if (larch.willSample('warn', 'thing failed!')) {
larch.swarn('thing failed!', {
count: this.count,
length: this.length,
largeArrayOfThings: this.bigArray,
hugeAmountOfUsefulDebuggingInfo: this.stuff
});
}
This way, we can do less work when we have a lot of logs because we don't have to allocate the large meta object.
Regular log methods (.log
, .error
, etc) will first compute a sampling
decision. Log methods prefixed with an s
(.slog
, .serror
, etc) will use
a previously computed sampling decision. Calling an s
method without first
calling .willSample($level, $msg)
will throw.
Contributors
License
MIT.