Help understanding data-in-memory true and evictions
https://discuss.aerospike.com/t/help-understanding-data-in-memory-true-and-evictions/1759


namespace test_ssd {
  high-water-memory-pct 80
  high-water-disk-pct   50
  stop-writes-pct       90

  memory-size 100G

  storage-engine device {
    device /dev/sdb1 ## 200G
    write-block-size 128k
    data-in-memory true
  }
}


There are 3 main configuration options, SSD persisted, RAM only, or RAM with persistence (on HDD or SSD). 
You cannot have ‘some of the data in RAM’ and some (more) on SSD. 
And yes, there is a ‘write cache’ configurable through the post-write-queue  configuration parameter.

https://www.aerospike.com/docs/reference/configuration/#post-write-queue

The confusion may come from the delete mechanism, 
which will remove the entry in RAM only (no tomb-stoning on SSD) 
and let the data on the device (until the write block goes through the defragmentation and new data written over it). 
So, in case of cold start, some of the deleted data may come back.


有3个主要的配置选项，SSD持久化、仅RAM或具有持久性的RAM(在HDD或SSD上)。
不能在RAM中有一些数据，而在SSD中有一些(更多)数据。
写缓存 配置参数 post-write-queue

混淆可能来自删除机制，只删除RAM中的条目(SSD上没有墓碑)
让设备上的数据(直到 write block 完成碎片整理并在上面写入新数据)。
因此，在冷启动时，一些删除的数据可能会返回。



Data in memory with persistence to disk means that the data is written to DRAM, 
and queued for the disk, with that queue flushed to disk periodically or when the buffer is full.



Eventually Persistent
data is written to the memory and also written asynchronously to the SSD.


Is it possible to keep recently used data in-memory and other on SSD  
https://discuss.aerospike.com/t/is-it-possible-to-keep-recently-used-data-in-memory-and-other-on-ssd-aer-5944/1032

Presently such partial caching of data is not supported in aerospike.
不支持热点数据在内存，其他数据在硬盘上


Data-in-memory evictions
https://discuss.aerospike.com/t/data-in-memory-evictions/408

Once Aerospike hits the high-water-mark for memory usage it starts evicting the oldest non 0 TTL data. 
Is this data evicted from SSD as well or does the data simply become unavailable in RAM?

Data is evicted/purged from both RAM and SSD.
数据会从内存和硬盘上逐出