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Memory vs. Harddisk???

Jonathan Culloty
Greenhorn

Joined: Apr 22, 2006
Posts: 16
Hello,

Could anyone suggest which is the best approach for the Server. Should data be held in memory (e.g. as a Vector) until the server is shutdown and then written to the db file. Or should the db file be constantly updated when a delete/create/update functions are called on the server.

I would prefer holding the Server data in memory until the server is shut down. I was going to justify this design choice with the following points in my choices.txt ...

Memory is cheap (a couple of thousand entries should not be a problem)
Simplier design (more maintainable)
Faster access times

Do you think this would be acceptable solution. Has anyone heard if keeping all the data in memory until shutdown is a no no.

Thanks,
Jon
Ulf Dittmer
Marshal

Joined: Mar 22, 2005
Posts: 42608
    
  65
Welcome to JavaRanch.

How about doing both - keeping it in memory for fast access, and writing it to disk for safety? Imagine someone tripping over a wire while nothing has been written to disk yet (yes, it does happen, even in hosting centers).


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Jeroen T Wenting
Ranch Hand

Joined: Apr 21, 2006
Posts: 1847
In order to prevent dataloss I keep everything on disc.
I don't even use a disk cache at the moment (though I could implement one) because it's IMO beyond the scope of the assignment (a small scale system).

When and if performance becomes an issue (which isn't listed in the requirements) a cache could easily be added.


42
Mihai Radulescu
Ranch Hand

Joined: Sep 18, 2003
Posts: 918

Hi, Jon

I keep in memory only a Map of record indexes(valid and active records).

Jeroen, you must do the something similar ? What you mean by :

I keep everything on disc.



Regards M


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Jeroen T Wenting
Ranch Hand

Joined: Apr 21, 2006
Posts: 1847
the only thing I keep in memory is the locks (of course) and a list of records that were deleted during the current session (just as a slight performance boost when inserting a new record, to prevent a complete tablescan for empty space).
 
It is sorta covered in the JavaRanch Style Guide.
 
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