Re: Completely un-tuned Postgresql benchmark results: SSD vs desktop HDD

[Karl Denninger <karl@xxxxxxxxxxxxx>]

Scott Marlowe wrote:

On Tue, Aug 10, 2010 at 12:13 PM, Karl Denninger <karl@xxxxxxxxxxxxx> wrote:
  

ANY disk that says "write is complete" when it really is not is entirely
unsuitable for ANY real database use.  It is simply a matter of time
    

What about read only slaves where there's a master with 100+spinning
hard drives "getting it right" and you need a half dozen or so read
slaves?  I can imagine that being ok, as long as you don't restart a
server after a crash without checking on it.
  

A read-only slave isn't read-only, is it?

I mean, c'mon - how does the data get there?

IF you mean "a server that only accepts SELECTs, does not accept UPDATEs or INSERTs, and on a crash **reloads the entire database from the master**", then ok.

Most people who will do this won't reload it after a crash.  They'll "inspect" the database and say "ok", and put it back online.  Bad Karma will ensue in the future.

Incidentally, that risk is not theoretical either (I know about this one from hard experience.  Fortunately the master was still ok and I was able to force a full-table copy.... I didn't like it as the database was a few hundred GB, but I had no choice.)

-- Karl

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