[FLINK-8707] Excessive amount of files opened by flink task manager

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Not A Problem
• Affects Version/s: 1.3.2
• Component/s: Runtime / Coordination

Environment

NAME="Red Hat Enterprise Linux Server"
VERSION="7.3 (Maipo)"

Two boxes, each with a Job Manager & Task Manager, using Zookeeper for HA.

flink.yaml below with some settings (removed exact box names) etc:

env.log.dir: ...some dir...residing on the same box
env.pid.dir: some dir...residing on the same box
metrics.reporter.jmx.class: org.apache.flink.metrics.jmx.JMXReporter
metrics.reporters: jmx
state.backend: filesystem
state.backend.fs.checkpointdir: file:///some_nfs_mount
state.checkpoints.dir: file:///some_nfs_mount
state.checkpoints.num-retained: 3
high-availability.cluster-id: /tst
high-availability.storageDir: file:///some_nfs_mount/ha
high-availability: zookeeper
high-availability.zookeeper.path.root: /flink
high-availability.zookeeper.quorum: ...list of zookeeper boxes
env.java.opts.jobmanager: ...some extra jar args
jobmanager.archive.fs.dir: some dir...residing on the same box
jobmanager.web.submit.enable: true
jobmanager.web.tmpdir:  some dir...residing on the same box
env.java.opts.taskmanager: some extra jar args
taskmanager.tmp.dirs:  some dir...residing on the same box/var/tmp
taskmanager.network.memory.min: 1024MB
taskmanager.network.memory.max: 2048MB
blob.storage.directory:  some dir...residing on the same box

• Assignee: Unassigned
• Reporter: Alexander Gardner
• Created: 19/Feb/18 19:16
• Updated: 28/Feb/19 14:11
• Resolved: 28/May/18 08:19

Description

The job manager has less FDs than the task manager.

 

Hi

A support alert indicated that there were a lot of open files for the boxes running Flink.

There were 4 flink jobs that were dormant but had consumed a number of msgs from Kafka using the FlinkKafkaConsumer010.

A simple general lsof:

$ lsof | wc -l       ->  returned 153114 open file descriptors.

Focusing on the TaskManager process (process ID = 12154):

$ lsof | grep 12154 | wc l    > returned 129322 open FDs

$ lsof -p 12154 | wc -l   -> returned 531 FDs

There were 228 threads running for the task manager.

 

Drilling down a bit further, looking at a_inode and FIFO entries: 

$ lsof -p 12154 | grep a_inode | wc -l = 100 FDs

$ lsof -p 12154 | grep FIFO | wc -l  = 200 FDs

$ /proc/12154/maps = 920 entries.

Apart from lsof identifying lots of JARs and SOs being referenced there were also 244 child processes for the task manager process.

Noticed that in each environment, a creep of file descriptors...are the above figures deemed excessive for the no of FDs in use? I know Flink uses Netty - is it using a separate Selector for reads & writes? 

Additionally Flink uses memory mapped files? or direct bytebuffers are these skewing the numbers of FDs shown?

Example of one child process ID 6633:

java 12154 6633 dfdev 387u a_inode 0,9 0 5869 [eventpoll]
java 12154 6633 dfdev 388r FIFO 0,8 0t0 459758080 pipe
java 12154 6633 dfdev 389w FIFO 0,8 0t0 459758080 pipe

Lasty, cannot identify yet the reason for the creep in FDs even if Flink is pretty dormant or has dormant jobs. Production nodes are not experiencing excessive amounts of throughput yet either.