Recovering from crash

[Derek Atkins]

Andrew Sullivan <ajs at anvilwalrusden.com> writes:

> On Tue, Oct 11, 2011 at 05:58:38PM -0400, Derek Atkins wrote:
>> Just a quick warning...  The log file will NOT replay business actions. 
>
> Why is this?  (This isn't a criticism, just a question.)

Because it's a "transaction log" and only logs transactions.  That's how
it's always been.  It doesn't log anything else.  It doesn't log changes
to Accounts, either, so if you added or deleted or otherwise modified an
account that change wont be recorded in the log.  It's always been like
that, since the beginning of the logging feature.

> In the somewhat-early days of PostgreSQL development, there was an
> idea that nifty new features could be added without logging (it's more
> complicated than this, but bear with me) support.  But the effect was
> that some of those features remained forever 2d class citizens.  Is
> that what's happening here?  Because if so, it'd be really great to
> know that now so that I can decide either (1) to fund development of
> those features or (2) to find something that will promise not to lose
> my data across system crashes.  (I will state now that (1) is
> unlikely, given what I'm looking at in terms of profit; but I might be
> willing to trade, and some money could be involved.)

No, that's not the case here.  It's the "logging" that's the
second-class citizen.  It has always been only transaction logging.
This was true even before the business features were added.  Indeed, the
"Log Replay" has always been somewhat of a hack as an interim stopgap to
help users in some cases until we could fully migrate to SQL, which is
the true answer for not losing any data.

>>From the documentation state, it's pretty clear that the business
> features aren't really the priority.  But losing posted invoices moves
> from "not a priority" to "this is a toy".  I had no idea that business
> actions weren't logged, and that isn't a prominently-displayed note in
> the manual last I checked, either.

If an application crashes you lose data.  Period.  That's true for
pretty much any application.  Even if you have autosave turned on, there
is still a window.  Show me any application that doesn't use a database
that will *never* lose data.

> Best,
>
> A

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       warlord at MIT.EDU                        PGP key available