# Grok failed to parse simple string and logstash stuck at 100% CPU

**URL:** <https://discuss.elastic.co/t/grok-failed-to-parse-simple-string-and-logstash-stuck-at-100-cpu/112895>\
**Category:** Logstash\
**Created:** [December 21, 2017, 9:15pm UTC](https://discuss.elastic.co/t/grok-failed-to-parse-simple-string-and-logstash-stuck-at-100-cpu/112895 "2017-12-21T21:15:01Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Vivien](https://avatars.discourse-cdn.com/v4/letter/v/a5b964/32.png) [@Vivien](https://discuss.elastic.co/u/Vivien)\
**Post date:** [December 21, 2017, 9:15pm UTC](https://discuss.elastic.co/t/grok-failed-to-parse-simple-string-and-logstash-stuck-at-100-cpu/112895/1 "2017-12-21T21:15:01Z")

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Hi!  
I've got a strange error:  
[2017-12-21T20:54:31,450][WARN][logstash.filters.grok] Timeout executing grok '%{UNIXPATH:path}/(?[^_]\*)_(?\<fs\_component\>[-.0-9a-z]+)\_(?\<fs\_logformat\>[A-Z]+).logs' against field 'source' with value '/var/fairshell/logs/docker-apps/waf.data.log.error.log\_demo-web\_APACHE.logs'!

After that the filebeat-logstash is locked and logstash consumes 100% CPU (that stops when I stop filebeat and starts again when filebeat is restarted) and no other event from filebeat is treated by logstash. After some (long, sometimes 30) minutes Logstash seems to work again.

I checked with the grok debugger that the value is correctly parsed by the grok expression.

Logstash's conf is quite simple here:  
grok {  
match =\> { "source" =\> "%{UNIXPATH:path}/(?[^_]\*)_(?\<fs\_component\>[-.0-9a-z]+)\_(?\<fs\_logformat\>[A-Z]+).logs" }  
remove\_field =\> ["dummy"]  
remove\_field =\> ["path"]  
}

Any idea what's wrong here?  
Thanks

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<div class="post-metadata">

**Author:** ![magnusbaeck](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/magnusbaeck/32/44943_2.png) [@magnusbaeck](https://discuss.elastic.co/u/magnusbaeck)\
**Post date:** [December 22, 2017, 7:21am UTC](https://discuss.elastic.co/t/grok-failed-to-parse-simple-string-and-logstash-stuck-at-100-cpu/112895/2 "2017-12-22T07:21:21Z")

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That's surprising, but try prepending the expression with `^` to reduce the amount of backtracking.

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<div class="post-metadata">

**Author:** ![Vivien](https://avatars.discourse-cdn.com/v4/letter/v/a5b964/32.png) [@Vivien](https://discuss.elastic.co/u/Vivien)\
**Post date:** [December 22, 2017, 1:26pm UTC](https://discuss.elastic.co/t/grok-failed-to-parse-simple-string-and-logstash-stuck-at-100-cpu/112895/3 "2017-12-22T13:26:11Z")

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Hi,  
I still get the error, but the 100% CPU problem has not come back (though i can't be sure if it's related):  
[2017-12-22T13:23:33,145][WARN][logstash.filters.grok] Timeout executing grok '^%{UNIXPATH:path}/(?[^_]\*)_(?\<fs\_component\>[-.0-9a-z]+)\_(?\<fs\_logformat\>[A-Z]+).logs' against field 'source' with value '/var/fairshell/logs/docker-apps/waf.data.log.error.log\_demo-web\_APACHE.logs'!  
Thanks!

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<div class="post-metadata">

**Author:** ![Badger](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/badger/32/25190_2.png) [@Badger](https://discuss.elastic.co/u/Badger)\
**Post date:** [December 22, 2017, 2:31pm UTC](https://discuss.elastic.co/t/grok-failed-to-parse-simple-string-and-logstash-stuck-at-100-cpu/112895/4 "2017-12-22T14:31:43Z")

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> [@Vivien](#):
>
> '^%{UNIXPATH:path}/(?[^]\*)(?\<fs\_component\>[-.0-9a-z]+)\_(?\<fs\_logformat\>[A-Z]+).logs'

1. Did something get lost in this? The first item after the / does not look like a valid group to me.

2. It looks like there are [known issues](https://github.com/logstash-plugins/logstash-patterns-core/issues/159) with UNIXPATH and excessive backtracking.

3. Can you get the job done with this?... (Note that I added \_ to the fs\_component pattern, so that demo-web goes to that side.)

```
match => { "message" => "/(?<fs_component>[-_.0-9a-z]+)_(?<fs_logformat>[A-Z]+).logs" }
```

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<div class="post-metadata">

**Author:** ![magnusbaeck](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/magnusbaeck/32/44943_2.png) [@magnusbaeck](https://discuss.elastic.co/u/magnusbaeck)\
**Post date:** [December 22, 2017, 2:34pm UTC](https://discuss.elastic.co/t/grok-failed-to-parse-simple-string-and-logstash-stuck-at-100-cpu/112895/5 "2017-12-22T14:34:13Z")

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> Did something get lost in this? The first item after the / does not look like a valid group to me.

Just the usual mangling of things that look like HTML.

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [January 19, 2018, 2:34pm UTC](https://discuss.elastic.co/t/grok-failed-to-parse-simple-string-and-logstash-stuck-at-100-cpu/112895/6 "2018-01-19T14:34:28Z")

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