Subject Re: [firebird-support] Re: FB database in RAM
Author Kjell Rilbe
Den 2011-08-03 15:13 skrev maik.sommer667 såhär:
> are you sure you can live with data loss in cause of system-
> powersupply- or emergency-shutdown-errors?

It would hurt but it wouldn't be critical. I weigh that loss against the
risk of it actually happening, and considering our hosting company has
rather substantial UPS resources in case of powerloss, I think it's
rather low risk. But RAM modules will fail sometimes and in case the
power supply fails the UPS won't help.

The system has higher speed requirements for reads than writes, and
writes are less common than reads, so one option could be to use
replication. I can think of two possible configurations here,
considering the web app can be split into two parts, where one part is
our internal data entry/update system and the other part is the public
select/extraction system.

Setup 1: Both parts work against the RAM database and we use replication
to a disk copy as a stage one backup. In case of powerloss with intacts
disks, we will only lose what hasn't been replicated to disk yet.

Setup 2: The internal data entry part works agains the disk database and
the public select part works against a RAM copy that's kept up to date
by means of replication from the one on disk. The select part needs to
save data about the selections for accounting etc, and it could do that
either to the RAM DB with replication to disk or redirect all writes to
the disk database. More complex, but in case of powerloss with intact
disks we would not lose any data at all.

> our database is about 42gb.

Ours is 56 Gbyte and growing.

> that is the cause why we`re backing up just
> once a day. it has it`s own raid1-volume, and for performance reasons i
> am planning to add a raid5 with 4 fast ssd`s.

> i think that could be a better option.

Yes, maybe. Could you give any stats on performance with such a setup
compared to regular RAID 1 with traditional 15 krpm scsi disks?

Kjell Rilbe
E-post: kjell@...
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