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Re: LMDB on Ramdisk (tmpfs)


> On 22 Mar 2018, at 11:37, Howard Chu <hyc@symas.com> wrote:

>> According to my understanding the memory is dirty when 1)there are open transactions, 2) the data has not been written back to the filesystem
> 
> Your understanding is incorrect. Dirty pages remain dirty until they are written to stable storage (e.g., disk). A tmpfs/RAMdisk has no stable storage, all of its pages reside only in RAM. That's the point of a RAMdisk.

Ok, thanks for have it clarified. I was just “hoping” LMDB would have not notice the type of storage was syncing to. 


>> What I don't understand is why there is a difference between filesystem and ramdisk? Is there any reason? The application (listed above) is not writing on the lmdb, but just reading (using reading transaction). Thank you Luca
> 
> Using tmpfs is a waste of RAM. Just use LMDB on a regular filesystem and let the system's pagecache manager take care of memory.

Got your point, but does make sense then to use a regular filesystem if the storage is a “slow” non-SDD Hard drive? 

Thanks
Luca