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Docs improved by adding more details about local cache and memory for segments on historicals.

This commit is contained in:
Oleg Zaezdny 2015-11-01 21:56:28 +02:00
parent 0eead6154a
commit 95a5ae0373
2 changed files with 2 additions and 2 deletions
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2
docs/content/configuration/caching.md
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@ -24,7 +24,7 @@ for both broker and historical nodes, when defined in the common properties file
#### Local Cache #### Local Cache
A simple in-memory LRU cache. A simple in-memory LRU cache. Local cache resides in JVM heap memory, so if you enable it, make sure you increase heap size accordingly.
|Property|Description|Default| |Property|Description|Default|
|--------|-----------|-------| |--------|-----------|-------|

2
docs/content/operations/performance-faq.md
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@ -10,7 +10,7 @@ The size of the JVM heap really depends on the type of Druid node you are runnin
[Broker nodes](../design/broker.html) uses the JVM heap mainly to merge results from historicals and real-times. Brokers also use off-heap memory and processing threads for groupBy queries. We recommend 20G-30G of heap here. [Broker nodes](../design/broker.html) uses the JVM heap mainly to merge results from historicals and real-times. Brokers also use off-heap memory and processing threads for groupBy queries. We recommend 20G-30G of heap here.
[Historical nodes](../design/historical.html) use off-heap memory to store intermediate results, and by default, all segments are memory mapped before they can be queried. Typically, the more memory is available on a historical node, the more segments can be served without the possibility of data being paged on to disk. On historicals, the JVM heap is used for [GroupBy queries](../querying/groupbyquery.html), some data structures used for intermediate computation, and general processing. One way to calculate how much space there is for segments is: memory_for_segments = total_memory - heap - direct_memory - jvm_overhead. [Historical nodes](../design/historical.html) use off-heap memory to store intermediate results, and by default, all segments are memory mapped before they can be queried. Typically, the more memory is available on a historical node, the more segments can be served without the possibility of data being paged on to disk. On historicals, the JVM heap is used for [GroupBy queries](../querying/groupbyquery.html), some data structures used for intermediate computation, and general processing. One way to calculate how much space there is for segments is: memory_for_segments = total_memory - heap - direct_memory - jvm_overhead. Note that total_memory here refers to the memory available to the cgroup (if running on Linux), which for default cases is going to be all the system memory.
We recommend 250mb * (processing.numThreads) for the heap. We recommend 250mb * (processing.numThreads) for the heap.