[erlang-questions] Mnesia and the 4Gb Limit

Dan Gudmundsson <>
Fri Feb 15 10:59:40 CET 2008


Only tables with storage 'disc_only_copies' uses dets,  disc_copies uses 
disk_log to store the data.

/Dan

Chandru wrote:
> On 14/02/2008, David Lloyd <> wrote:
>>  Hi There,
>>
>>  Does Mnesia/Dets still have the 4GB limit? Answers I've found on the
>>  'net seem to indicate that 64bit Erlang has, essentially, erased this limit.
>>
>>  I'm looking at a database table that miht be larger than 4Gb; it's
>>  already an in memory, MySQL table (MySQL cluster uses an in memory table
>>  structure) so I don't seem to have a "lack" of memory [last time I
>>  looked the min. memory in any one node on this cluster is 8Gb).
>>
> 
>>From reading the manuals, it looks like dets still has this limit.
> What 64 bit erlang does is remove the restriction that an erlang node
> can only address 4GB of memory. This basically means you can have a
> database of more than 4GB, but *each* mnesia table on disk cannot be
> more than 2GB. You can use table fragmentation to get around this. I
> guess this restriction won't apply to mnesia ram_copies tables.
> 
> I have created databases of up to 15GB without any problem using 64
> bit erlang, but they were fragmented disc_copies tables.
> 
> cheers
> Chandru
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