I was optimizing a 3 GB table as a MEMORY table in order to do some analysis on it, and I was curious if adding indexes even help a MEMORY table. Since the data is all in memory anyway, is this just redundant?
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I was optimizing a 3 GB table as a MEMORY table in order to do some analysis on it, and I was curious if adding indexes even help a MEMORY table. Since the data is all in memory anyway, is this just redundant?
No, they’re not redundant.
Yes, continue to use indexes.
The speed of access to a memory table on smaller tables with a non-indexed column may seem almost identical to the indexed ones due to how fast full table scans can be in memory, but as the table grows or as you join them together to make larger result sets there will be a difference.
Regardless of the storage method the engine uses (disk/memory), proper indexes will improve performance as long the storage engine supports them. How the indexes are implemented may vary, but I know they are implemented in the table types MEMORY, INNODB, and MyISAM. BTW: The default method for indexes in MEMORY tables is with a hash instead of a B-Tree.
Also, I generally don’t recommend coding to your storage engine. What’s a memory table today may need to changed to innodb tomorrow–the SQL and schema should stand on it’s own.