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Beyond top(1) Command-Line Monitoring on the JVM Colin Jones @trptcolin 8th Light

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No content

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What to expect

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command-line tooling

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on the JVM

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introspection & serviceability

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--all-flags=false

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war stories

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real-life usage (well, re-enacted anyway)

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A long time ago in a software shop far, far away…

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Things are going pretty well

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What does this thing look like? app-architecture Postgres Web / API Application Server Load Balancer Periodic Job Application Server 3rd-party Service A 3rd-party Service B Monitored email account End users: native mobile app Admin users: desktop browsers

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But strange things are afoot

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the server sometimes gets really slow

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the team has to manually restart the application server

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incident response time is ~5 minutes

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Yes, strange things are afoot

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Pain, frustration, anger

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Just the facts

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sometimes, things get slow

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all requests seem to be affected

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the JVM stays up

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restart the JVM and everything is fine

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What could it be?

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Demo

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More facts, please!

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constant full GCs

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what’s in the heap

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what application code was running

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The right tools for the job

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vmstat system-level: CPU, memory, disk, context switching

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top per-process: CPU & memory

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jps what’s our PID?

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jstack status of all threads (right now-ish!)

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jcmd what can’t it do?! jcmd [PID] help (sorry, JVM 6 users: see jinfo/jmap/jstack)

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jstat GC classloader compiler

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Mystery solved!

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Now “just” fix it

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idea 1: eliminate the leak

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idea 2: eliminate the cache altogether?

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idea 3: delete the feature

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idea 4: full-text search engine

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So we’re good now… until the next incident

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Lessons

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“it’s slow” could mean lots of things

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“high CPU” could mean lots of things

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collecting data is crucial in a crisis

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reproducing the issue helps me sleep at night

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Other “right tools for the job”

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Heap analyzers

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Profilers

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Constant monitoring & alerting

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Dynamic tracing

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Learning more

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Books

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operators are standing by! man jstat man jstack jcmd [PID] help [COMMAND] etc.

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Thank you! Colin Jones @trptcolin 8th Light