: "user@cassandra.apache.org"
Date: Wednesday, April 22, 2020 at 7:23 AM
To: "user@cassandra.apache.org"
Subject: Re: Impact of setting low value for flag -XX:MaxDirectMemorySize
Message from External Sender
I am running spark (max heap 4G) and a java application (4G) with my C
very busy… and if it’s very busy then it’s likely
> using it’s buffers as they are intended.
>
>
>
> *From: *HImanshu Sharma
> *Reply-To: *"user@cassandra.apache.org"
> *Date: *Saturday, April 18, 2020 at 2:06 AM
> *To: *"user@cassandra.apache.org"
&g
they are intended.
From: HImanshu Sharma
Reply-To: "user@cassandra.apache.org"
Date: Saturday, April 18, 2020 at 2:06 AM
To: "user@cassandra.apache.org"
Subject: Re: Impact of setting low value for flag -XX:MaxDirectMemorySize
Message from External Sender
From th
There are a handful of offheap uses
- bloom filters (scale approximately linearly with data size based on your
bloom filter false positive ratio)
- compression metadata, scales linearly with data size based on your
compression chunk size
- Partition indexes
- Netty For client / server requests.
>From the codebase as much I understood, if once a buffer is being
allocated, then it is not freed and added to a recyclable pool. When a new
request comes effort is made to fetch memory from recyclable pool and if is
not available new allocation request is made. And while allocating a new
request
Like most things, it depends on (a) what you're allowing and (b) how much
your nodes require. MaxDirectMemorySize is the upper-bound for off-heap
memory used for the direct byte buffer. C* uses it for Netty so if your
nodes are busy servicing requests, they'd have more IO threads consuming
memory.
What will be the impact of setting the value of XX:MaxDirectMemorySize to
some low value. Currently default value for off heap is equal to heap
memory.
I saw this open ticket discussing this but could not infer much from it.
https://issues.apache.org/jira/browse/CASSANDRA-10930
Regards
Manish
