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From Fay Hou [Storage Service] ­ <>
Subject Re: Cassandra crashes....
Date Tue, 22 Aug 2017 14:57:57 GMT
What errors do you see?
16gb of 256 GB . Heap is too small. I would give heap at least 160gb.

On Aug 22, 2017 7:42 AM, "Thakrar, Jayesh" <>

Hi All,

We are somewhat new users to Cassandra 3.10 on Linux and wanted to ping the
user group for their experiences.

Our usage profile is  batch jobs that load millions of rows to Cassandra
every hour.

And there are similar period batch jobs that read millions of rows and do
some processing, outputting the result to HDFS (no issues with HDFS).

We often seen Cassandra daemons crash.

Key points of our environment are:

*Pretty good servers:* 54 cores (with hyperthreading), 256 GB RAM, 3.2 TB
SSD drive

*Compaction:* TWCS compaction with 7 day windows as the data retention
period is limited - about 120 days.

*JDK: *Java and G1 GC

*Heap Size:* 16 GB

*Large SSTables:* 50 GB to 300+ GB

We see the daemons crash after some back-to-back long GCs (1.5 to 3.5

Note that we had set the target for GC pauses to be 200 ms

We have been somewhat able to tame the crashes by updating the TWCS
compaction properties

to have min/max compaction sstables = 4 and by drastically reducing the
size of the New/Eden space (to 5% of heap space = 800 MB).

Its been about 12 hours and our stop-the-world gc pauses are under 90 ms.

Since the servers have more than sufficient resources, we are not seeing
any noticeable performance impact.

Is this kind of tuning normal/expected?



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