Re: BDB memory cache problem

[Howard Chu <hyc@symas.com>]

Szuts Attila wrote:

> Is there any way to turn off BDB memory_cacheing_to_disk ?
> (__db.001 and other files) At least for write operations?
>
> Most of the times this files causes data loss, when OS system crashes.
> If I unterstand it right: 
> 1. BDB waiting until memory buffer is full, 
> 2. then write data to disk I/O buffer
>  
The BDB cache resides in memory-mapped files by default. So there is no 
step 2, all writes to the memory buffer are automatically paged to disk 
by the operating system.

> 3. then will be written data to *.bdb files.
> Between 1 and 2 data is written to log.000000* file, but after OS recovering  
> there is always some data I can't read.
>
> If OS fails and BDB memory buffer is not flushed, then data will loss. As I see this is 
> persistent problem in BDB over the time.
>  
That's what the db_recover command is for, to replay events from the log 
files back into the database.

--
 -- Howard Chu
 Chief Architect, Symas Corp.       Director, Highland Sun
 http://www.symas.com               http://highlandsun.com/hyc
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