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From Jason Heo <jason.heo....@gmail.com>
Subject Question about memory_limit_hard_bytes and
Date Mon, 24 Apr 2017 15:24:59 GMT
Hello.

I'm using Apache Kudu 1.3.0.

I found some explanation in manual and cdh about memory_limit_hard and
block_cache_capacity But I couldn't understand what are they exactly used
for, what is stored at block_cache, and what's the meaning of hard limit of
memory?

In Kudu Configuration Reference:

   - *memory_limit_hard_bytes
   <https://kudu.apache.org/docs/configuration_reference.html#kudu-tserver_memory_limit_hard_bytes>*:
   Maximum amount of memory this daemon should use, in bytes. A value of 0
   autosizes based on the total system memory. A value of -1 disables all
   memory limiting.
   - *block_cache_capacity_mb
   <https://kudu.apache.org/docs/configuration_reference.html#kudu-tserver_block_cache_capacity_mb>*:
   block cache capacity in MB


In Cloudera Manager's help:

   - *memory_limit_hard_bytes*: Maximum amount of memory that the Kudu
   Tablet Server will use before it starts rejecting all incoming writes.
   - *block_cache_capacity_mb*: Maximum amount of memory allocated to the
   Kudu Tablet Server's block cache.

Is hard_limit related with insert/update/delete and is not related to
performance of read? Does block_cache store tablet data? Then what's the
relationship with page cache.

After watching Comcast presentation, I was surprised because they are using
memory_limit_hard=4G, block_cache=512MB.

Regards,

Jason

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