Database Features
Tips and Tricks on using Exasol - from SQL and Lua Scripts to transactions and performance
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Question With Exasol's automated disk and memory management, it its not always easy to answer questions like How much data is stored in the database? How much disk space do I use? How much memory is in use? How much disk space is left? And how much more data can I actually store? Answer This article addresses a few of those questions by giving an overview of the relations between the different values one can read from Exasol's system tables or web management interface (EXAoperation). Overview Have a look at the following diagram showing the general relationships between many of the keywords used when talking about data sizes in Exasol:       Notes: The ratio between   RAW_   and   MEM_OBJECT_SIZE   is what Exasol commonly defines as   compression ratio The distinction between   RAW   and   MEM   sizes also applies to system data: Everything is   compressed in RAM   and mapped to/from disk. Usually there is no need to fit all of the data into DB RAM. Systems with a large amount of /passive data/ may perform well with 10% of   DB_RAM   compared to overall   MEM_OBJECT_SIZE A typical "first guess" estimation for required   DB_RAM   is about 10% of the expected   RAW_OBJECT_SIZE While   deleted blocks   in storage are reused by later operations, as a general rule, storage volumes   do not shrink   unless forced to do so. In   DB_RAM , the ratio between active data and temp data is flexible, but temp is hard-limited at 80%. Information Location Object Level Metric Location Comment RAW_OBJECT_SIZE System table   EXA_DBA_OBJECT_SIZES Theoretical value, never actually required MEM_OBJECT_SIZE System table   EXA_DBA_OBJECT_SIZES   Index size AUXILIARY_SIZE   in System table   EXA_DBA_INDICES   Statistics + Audit Size STATISTICS_SIZE   in System table   EXA_STATISTICS_OBJECT_SIZES   HDD_READ / HDD_WRITE N/A   Database Level Metric Location Comment RAW_OBJECT_SIZE System table   EXA_DB_SIZE_LAST_DAY   MEM_OBJECT_SIZE System table   EXA_DB_SIZE_LAST_DAY   Index Size System table   EXA_DB_SIZE_LAST_DAY   Statistics+Audit Size System table   EXA_DB_SIZE_LAST_DAY   HDD_READ / HDD_WRITE System Table   EXA_MONITOR_LAST_DAY   DB_RAM Size System table   EXA_SYSTEM_EVENTS You can assume that the database will always "use" all that RAM and does not yield to others. RECOMMENDED_DB_RAM_SIZE System table   EXA_DB_SIZE_LAST_DAY   TEMP_DB_RAM_SIZE System Table   EXA_MONITOR_LAST_DAY == (DB_RAM:temp + Temporary:used) DB_RAM:active data N/A   DB_RAM:temp see Node Level below   Persistent:size STORAGE_SIZE   in   EXA_DB_SIZE_LAST_DAY   Persistent:committed see Node Level below ~= ( MEM_OBJECT_SIZE + AUXILIARY_SIZE + STATISTICS_SIZE ) Persistent:deleted see Node Level below size = committed * (100 / USE )   Node Level EXASOL 6.0.0   introduces a new system table for more detailed storage usage:   EXA_VOLUME_USAGE Please refer to the user manual or column comments for details on the columns. Metric Location Comment Persistent:size sum(VOLUME_SIZE) Size is always synchronized across nodes Persistent:committed data sum(COMMIT_DATA)   Temporary:used sum(SWAP_DATA)   Temporary:unused sum(UNUSED_DATA)     Storage Level Metric Location Comment Persistent Volume Size EXAStorage -> (Labels: <dbname>_persistent) -> Size == Persistent:size from Database level Temporary Volume Size EXAStorage -> (Labels: <dbname>_temporary) -> Size   Exists Slave Segment? EXAStorage -> persistent -> Redundancy Gives total number of copies: 1 == no redundancy Free Disk Space EXAStorage -> Space on Disks -> sum(sum:free)   Free database (disk) space See  how-to-monitor-free-database-disk-space      
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