Re: purging double spend db

On Fri, Oct 08, 2004 at 12:16:08PM -0400, Atom 'Smasher' wrote:
> On Fri, 8 Oct 2004, Adam Back wrote:
> >If this is all inconvenient for what you are doing or anyway for 
> >completeness of control I maybe could make -e available with -p and make 
> >it purge all stamps (or those matched by the optional -j pattern) as if 
> >they were originally given expiry period given with -e.  Ie the -p flag 
> >given with -e overrides the one given with -cd.
> ===================
> 
> so, if that were implemented, 

In fact I implemented between the previous email and now.  Quite easy
to add :-)  (Not released yet).

> then i could expire spent stamps after X days?

Sure.  It would be just as if you'd given -e X when spending them.

In fact you can already in effect.

So say X days is your target (default is 28 days).

Already you can do this as you spend them:

	hashcash -cdb20 -r [email protected] -e Xd

and every day say from cron:

	hashcash -p now

or add to every invocation the purge option:

	hashcash -cdb20 -r [email protected] -e Xd -p 1d

which saves needing to use cron.

QED.


Now with this new feature you could in addition change your mind and
override the period you gave:

Eg. say you had been doing:

	hashcash -cdb20 -r  [email protected] -e Yd

Then 

	hashcash -p now

will only expire them as they need to be expired according to period
Y.  But this:

	hashcash -p now -e Xd

would expire them as if you gave X when you spent them (overriding the
Ydays you gave).

In fact I think this would be equivalent to:

	hashcash -p now -t +Nd

where N = Y-X (or -t -Md where M=X-Y).

So those two commands would do roughly the same thing.

> but for now, if i understand this correctly, a purge will get rid of
> spent stamps only after they're expired;

right.  Well you can override it to to delete them even though they
aren't expired with "-p now -k" which deletes also unexpired stamps.

> this is determined at the time they're spent, using the "-e" option;
> and by default stamps older than 2419200s (28d) will be purged.

Yes.

> where does the 2d grace period come into play when expiring spent
> stamps?

Well I need to not remove them from the double-spend db until they
would be considered invalid due to age.  This means I should keep
things in the double-spend db 2days longer (default grace period) than
you would otherwise think.

In fact the current version (1.12 and earlier) do not do this.  That
is the other change I just made which will release as 1.13 presently.

(If you don't do this you open a window where a spammer could re-spend
spent stamps after they've been purged but before they would be
considered invalid).

You can work around this by adding -t -2d to the purge line.

Adam