This document discusses debugging memory leaks in Node.js applications. It provides an overview of tools for detecting leaks such as node-memwatch, mdb and manta, and heapdump. These tools can monitor memory usage, detect leaks, and take heap snapshots for analysis. The document also shares examples of using these tools and reveals that third-party packages can sometimes contain leaks, so profiling early is important to understand application performance characteristics and identify potential issues.

1. DEBUGGING MEMORY LEAKS IN NODE APPS
jason wilson

2. OVERVIEW
whatis recommendo?
what's thatdrippingsound?
tools for huntingdown aleak

4. TRAFFIC PATTERN

5. CODE AT A GLANCE
7944 LOC
94 files

6. CODE AT A GLANCE
var express = require('express')
, http = require('http')
, _ = require('underscore')
, models = require('./models')
, AWS = require('aws-sdk');
require("long-stack-traces")
function batchGetRecommendations(req, res, next) {
var placement = req.placement;
async.waterfall([
function pickRecommendationStrategy(err, callback) {
_.each(strategies, function(strategy) {
fetchRecsFromDatabase(strategy, context, function(err, recs) {
recommenations.push(recs);
})
});
callback(recommendations);
}
,
function collateRecs(recs, callback) {
_.recs(recs, function(recommendation) {
// do some stuff
})
callback(recs);
}],
function(err, results) {
if(err) {
res.send(404)
} else {
res.send(results)
}
});
}

7. MACHINE SPECS:
c1 . medium ec2 instances
1.7 gb memory, 64-bit
2 virtualcores
node v10.22
cluster module

8. Rajesh

11. aclue...
(node)warning:possibleEventEmittermemoryleakdetected.11listenersadded.Usee
mitter.setMaxListeners()toincreaselimit.
Trace
atSocket.(events.js:160:15)
atSocket.(_stream_readable.js:689:33)
atServerResponse.assignSocket(http.js:1111:10)
atHTTPParser.onIncoming(http.js:2065:11)
atHTTPParser.parserOnHeadersComplete[asonHeadersComplete](http.js:121:23)
atSocket.ondata(http.js:1966:22)
atTCP.onread(net.js:527:27)

12. Whatis the v8 memorylimiton 64bitlinux?

15. easilyreproduced usingjmeter + ec2 instance :)

16. testcase memoryusage

17. Where is our memorygoing?

18. TOOLS AVAILABLE
node-memwatch
mdb + manta
heapdump + chrome developer tools

19. node-memwatch provides evented memorystats

20. memwatch example
module.exports=function(){
varmemwatch=require('memwatch');
varhd=null;
memwatch.on('leak',function(info){
console.log("Leakdetected:"+JSON.stringify(leak));
});
memwatch.on('stats',function(stats){
if(hd!=null){
vardiff=hd.end();
console.log("Heapdiff:"+JSON.stringify(diff));
}
hd=newmemwatch.HeapDiff();
});
};

21. more than adrip...
{
"start":"2014-07-17T01:19:37.000Z",
"end":"2014-07-17T01:20:03.000Z",
"growth":7422192,
"reason":"heapgrowthover5consecutiveGCs(26s)-980.08mb/hr"
}

22. heap diff
{
"before":{
"nodes":275235,
"time":"2014-07-17T01:07:16.000Z",
"size_bytes":32540169,
"size":"31.03mb"
},
"after":{
"nodes":281030,
"time":"2014-07-17T01:07:19.000Z",
"size_bytes":33685970,
"size":"32.13mb"
},
"change":{
"size_bytes":1145801,
"size":"1.09mb",
"freed_nodes":31294,
"allocated_nodes":37090,
"details":[
{
"what":"Arguments",
"size_bytes":-120,
"size":"-120bytes",
"+":3,
"-":6
},
{
"what":"Array",
"size_bytes":410568,
"size":"400.95kb",

23. mdb + manta

49. Error objects butwe can'tfind outwhat's referencingthem

51. heapdump allows for periodic snapshots of heap, can examine in
chrome developer tools

52. heapdump example
varheapdump=require('heapdump');
...
heapdump.writeSnapshot('/tmp/'+Date.now()+'.heapsnapshot');

53. module.exports=function(){
varheapdump=require('heapdump')
varBYTES_IN_MEGABYTE=1048576;
varREPORT_MEMORY_INTERVAL=60*1000;//60seconds
varnextMBThreshold=0;
setInterval(function(){
varmemMB=process.memoryUsage().rss/BYTES_IN_MEGABYTE;
if(memMB>nextMBThreshold){
console.log("Takingsnapshot.");
heapdump.writeSnapshot()
nextMBThreshold+=100;
}
},REPORT_MEMORY_INTERVAL)
}

64. TAKEAWAYS...
node-memwatch
mdb + manta
heapdump + chrome developer tools

65. TAKEAWAYS...
powerfulbuteasyto use tools available
profile earlyto undertsand perf characteristics
seeminglybenign packages can have memoryleaks

66. questions?