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| Guest |
 Posted: Tue Jul 04, 2006 7:37 pm |
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Guest
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I liked the cheap solution:
oid() -> {node(), erlang:now()}.
but how can I turn erlang:now() into a String ?? (which probablly
won't look very URL-friendly)
I thouhgt of turing it into a list, then into a binary, then base64
encoding it, but
list_to_binary(tuple_to_list(erlang:now()))
does not work.
regards
Roberto
On 6/30/06, Ulf Wiger (AL/EAB) <ulf.wiger@ericsson.com> wrote:
>
> I sketched the attached code for maintaining a node-specific sequence
> number in a cluster of nodes. The code is untested - probably doesn't
> even compile, and upon reflection, I'd do away with all the dirty ops.
> Basically, you should never use dirty ops on replicated tables.
>
> The thing I was after was a system-unique object identifier which was
> compact enough to be human- and URL-friendly.
>
> For cheap(in terms of CPU cost) automatic primary keys, I tend to use
>
> oid() -> {node(), erlang:now()}.
>
> Given a reasonably well-behaved system clock(*), this is certain to give
> unique values - increasing values, even - each time.
>
> (*) AFAIK, even though it's not documented, erlang:now() is derived from
> sys_gethrtime(), except on Win32, where it's derived from GetTickCount()
> - I gave up before understanding from the source how erlang:now()
> relates to "zero hour" on Windows. A cursory inspection of the code made
> me doubt that my statement holds true for Windows. Correct me, please,
> anyone.
>
> BR,
> Ulf W
>
> > -----Original Message-----
> > From: owner-erlang-questions@erlang.org
> > [mailto:owner-erlang-questions@erlang.org] On Behalf Of Roberto Saccon
> > Sent: den 30 juni 2006 03:59
> > To: erlang-questions@erlang.org
> > Subject: mnesia primary key creation
> >
> > I am wondering whether experienced erlang developers have
> > something better in their best-practises-treasure-box than
> > what I have come up with to create mnesia primary keys:
> >
> > 1. use "ordered_set" tables
> >
> > 2. use "mnesia:dirty_last(myTable)" to get the last inserted
> > key and increment it for a new key before inserting a new record.
> >
> >
> > regards
> > --
> > Roberto Saccon
> >
>
>
>
--
Roberto Saccon
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| uffe |
| Posted: Tue Jul 04, 2006 9:23 pm |
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Joined: 02 Mar 2005
Posts: 365
Location: Sweden
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Den 2006-07-04 21:31:26 skrev Roberto Saccon <rsaccon@gmail.com>:
> I liked the cheap solution:
>
> oid() -> {node(), erlang:now()}.
>
> but how can I turn erlang:now() into a String ?? (which probablly
> won't look very URL-friendly)
>
> I thouhgt of turing it into a list, then into a binary, then base64
> encoding it, but
> list_to_binary(tuple_to_list(erlang:now()))
> does not work.
Well, for example:
1> {Node,{MS,S,US}} = {node(), erlang:now()}.
{nonode@nohost,{1152,47770,297000}}
2>
list_to_binary([atom_to_list(Node),"-",integer_to_list(MS),"-",integer_to_list(S),"-",integer_to_list(US)]).
<<110,111,110,111,100,101,64,110,111,104,111,115,116,45,49,49,53,50,45,52,55,55,55,48,45,50,57,55,48,...>>
3> binary_to_list(v(2)).
"nonode@nohost-1152-47770-297000"
BR,
Ulf W
--
Ulf Wiger
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| Guest |
| Posted: Tue Jul 04, 2006 9:42 pm |
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Guest
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Thanks, after seeing the example it looks soooo simple and obvious !
On 7/4/06, Ulf Wiger <ulf@wiger.net> wrote:
> Den 2006-07-04 21:31:26 skrev Roberto Saccon <rsaccon@gmail.com>:
>
> > I liked the cheap solution:
> >
> > oid() -> {node(), erlang:now()}.
> >
> > but how can I turn erlang:now() into a String ?? (which probablly
> > won't look very URL-friendly)
> >
> > I thouhgt of turing it into a list, then into a binary, then base64
> > encoding it, but
> > list_to_binary(tuple_to_list(erlang:now()))
> > does not work.
>
> Well, for example:
>
> 1> {Node,{MS,S,US}} = {node(), erlang:now()}.
> {nonode@nohost,{1152,47770,297000}}
> 2>
> list_to_binary([atom_to_list(Node),"-",integer_to_list(MS),"-",integer_to_list(S),"-",integer_to_list(US)]).
> <<110,111,110,111,100,101,64,110,111,104,111,115,116,45,49,49,53,50,45,52,55,55,55,48,45,50,57,55,48,...>>
> 3> binary_to_list(v(2)).
> "nonode@nohost-1152-47770-297000"
>
> BR,
> Ulf W
>
> --
> Ulf Wiger
>
--
Roberto Saccon
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| Thomas Lindgren |
| Posted: Tue Jul 04, 2006 10:03 pm |
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User
Joined: 09 Mar 2005
Posts: 284
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--- Ulf Wiger <ulf@wiger.net> wrote:
> Den 2006-07-04 21:31:26 skrev Roberto Saccon
> <rsaccon@gmail.com>:
>
> > I liked the cheap solution:
> >
> > oid() -> {node(), erlang:now()}.
> >
> > but how can I turn erlang:now() into a String ??
> (which probablly
> > won't look very URL-friendly)
> >
> > I thouhgt of turing it into a list, then into a
> binary, then base64
> > encoding it, but
> > list_to_binary(tuple_to_list(erlang:now()))
> > does not work.
>
> Well, for example:
>
> 1> {Node,{MS,S,US}} = {node(), erlang:now()}.
> {nonode@nohost,{1152,47770,297000}}
> 2>
>
list_to_binary([atom_to_list(Node),"-",integer_to_list(MS),"-",integer_to_list(S),"-",integer_to_list(US)]).
>
<<110,111,110,111,100,101,64,110,111,104,111,115,116,45,49,49,53,50,45,52,55,55,55,48,45,50,57,55,48,...>>
> 3> binary_to_list(v(2)).
> "nonode@nohost-1152-47770-297000"
Or, a bit easier on the eyes (though perhaps a bit
more expensive):
fmt_oid({Node, {MS, S, US}}) ->
list_to_binary(
io_lib:format("~w-~w-~w-~w", [Node, MS, S, US])).
Best,
Thomas
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| Guest |
| Posted: Tue Jul 04, 2006 10:27 pm |
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Guest
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yeah, you are right, why not. Thanks for the suggestion.
regards
Roberto
On 7/4/06, RCB <rcbeerman@gmail.com> wrote:
> {T1, T2, T3} = now(),
> <<T1:16, T2:20, T3:20>>.
>
> Why not just generate a unique string?
>
> -module(randstr).
>
> -export([randstr/1, seedrand/0, seedrandstr/1]).
>
> chartab() ->
> { $a, $b, $c, $d, $e, $f, $g, $h, $i, $j, $k, $l, $m,
> $n, $o, $p, $q, $r, $s, $t, $u, $v, $w, $x, $y, $z,
> $A, $B, $C, $D, $E, $F, $G, $H, $I, $J, $K, $L, $M,
> $N, $O, $P, $Q, $R, $S, $T, $U, $V, $W, $X, $Y, $Z,
> $0, $1, $2, $3, $4, $5, $6, $7, $8, $9 }.
>
> seedrand() ->
> {S1, S2, S3} = now(),
> random:seed(S1,S2,S3),
>
> seedrandstr(N) ->
> seedrand(),
> randstr(N).
>
> randstr(N) ->
> C = chartab(),
> randstr(N,C,size(C),[]).
> randstr(0,_,_,Acc) ->
> Acc;
> randstr(N,C,Csz,Acc) ->
> randstr(N - 1, C, Csz, [element(random:uniform(Csz),C) | Acc]).
>
>
>
>
>
> On 7/4/06, Roberto Saccon <rsaccon@gmail.com> wrote:
> > I liked the cheap solution:
> >
> > oid() -> {node(), erlang:now()}.
> >
> > but how can I turn erlang:now() into a String ?? (which probablly
> > won't look very URL-friendly)
> >
> > I thouhgt of turing it into a list, then into a binary, then base64
> > encoding it, but
> > list_to_binary(tuple_to_list(erlang:now()))
> > does not work.
> >
> > regards
> > Roberto
> --
> Rich Beerman
> Cupertino, California
> mobile: 408/221-2444
> fax: 408/255-7944
>
--
Roberto Saccon
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