Getting Data In

Splunk re-indexing rolled over log file causing duplicate (two) copies of data

sfmandmdev
Path Finder

We have a log file rotation policy that rolls over based on size (64MB). For some reason, every now and then (frequent but not all the time), splunk forwarder thinks the rolled over file is a new file and ships it again causing duplicates in the indexer.

We would find the same event from filenames blah and blah.0 (rolledover file name).

Any clues what might be causing this issue?

dwaddle
SplunkTrust
SplunkTrust

How are you performing your roll-over? It is a rename or a copy?

0 Karma

hmahendrakumar
Path Finder

It is a rename.
Note: ZFS is underlying FS
Each process has a lot of threads that
write to log files protected by a mutex. So only one thread can write at a time.
When we see the file growing to exceed this size (~64MB), we acquire the mutex
blocking any writes to the file, closing the file, deleting oldest generation N (BLAHFILENAME.N)
then for (n = 0; n < N; n++) rename BLAHFILENAME.N to BLAHFILENAME.N+1
then finally renaming current log file BLAHFILENAME to BLAHFILENAME.0
then creating a new empty log file BLAHFILENAME and releasing the mutex
allowing all threads to write to the new file.

0 Karma

sfmandmdev
Path Finder

We don't have any crcSalt settings set. Also this does not happen all the time i.e All rolled over versions of the same log file are not duplicated.

0 Karma

Ayn
Legend

Do you have any particular crcSalt settings set in inputs.conf for this particular source?

0 Karma
Get Updates on the Splunk Community!

Last Chance to Submit Your Paper For BSides Splunk - Deadline is August 12th!

Hello everyone! Don't wait to submit - The deadline is August 12th! We have truly missed the community so ...

Ready, Set, SOAR: How Utility Apps Can Up Level Your Playbooks!

 WATCH NOW Powering your capabilities has never been so easy with ready-made Splunk® SOAR Utility Apps. Parse ...

DevSecOps: Why You Should Care and How To Get Started

 WATCH NOW In this Tech Talk we will talk about what people mean by DevSecOps and deep dive into the different ...