One thing we were guessing at with Massimo yesterday is, if you
store
large blobs as disk data, how much will they consume DataMemory
and
IndexMemory (primary key, each "chunk" has a hidden primary key,
first 25x bytes
of blob stored in memory...)?
My empirical test showed that about 2% of the total size
of blobs is needed for RAM
(25% of that is IndexMemory).
IMHO this is close to negligible, but in many situations not
negligible
at all (may have close to TB of disk data -> 20GB of RAM
needed for
disk data).
Also note that this is a minimum figure. If you actually have
something
else than the blob (like other indexes) you of course use much
more RAM.
The test was:
CREATE TABLE `jpgtest` (
`id` int(11) NOT NULL,
`jpg` blob,
PRIMARY KEY (`id`)
) TABLESPACE ts_1 STORAGE DISK ENGINE=ndbcluster;