Comments

• Abhishek_Rana Vertica Employee Employee

  April 2014

  Hi,
  
  Vertica does not cache queries (either plans or results). There is a modest cache of uncompressed data blocks Vertica maintains internally to avoid decompression on blocks reused quickly.
  To invalidate this cache, run a Vertica query on lots of data unrelated to the query to measure (this may also help invalidate the kernel disk cache).
  
  Vertica uses the Linux file-system cache for caching large amounts of data.The most likely caching effect is the kernel's use of memory to store recently accessed disk blocks.
  
  On NUMA (Non-uniform memory access) machines, cached memory usage has been found low ir-respective of cache availability. The kernel default on NUMA machines with zone_reclaim_mode=1 does not play well with caches. Changing the configuration to 0 fixes the bad caching behavior. 
  
  Regards'
  
  Abhishek

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• Navin_C Vertica Customer ✭

  April 2014

  what is the way to tell vertica to use maximum of memory(RAM)

  There is a modest cache of uncompressed data blocks Vertica maintains internally to avoid decompression on blocks reused quickly.
  

  Does this mean, Once I tried a select query and the result set gets stored in memory , then If I again fire the same query, vertica will access the data from memory .
  
  And how do understand if the data is uncompressed while reading.
  
  

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