<!-- MHonArc v2.4.4 -->
<!--X-Subject: Re: Unique id's -->
<!--X-From-R13: pbqreNvoz.arg -->
<!--X-Date: from tacitus.globecomm.net [207.51.48.7] by mx3.ibm.net id 860828145.98328-1 Sat Apr 12 06:55:45 1997 -->
<!--X-Message-Id: 199704120700.HAA575052#out2,ibm.net -->
<!--X-Content-Type: text/plain -->
<!--X-Reference: 199704120458.EAA318871#out1,ibm.net -->
<!--X-Head-End-->
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head>
<title>MUD-Dev message, Re: Unique id's</title>
<!-- meta name="robots" content="noindex,nofollow" -->
<link rev="made" href="mailto:coder#ibm,net">
</head>
<body background="/backgrounds/paperback.gif" bgcolor="#ffffff"
text="#000000" link="#0000FF" alink="#FF0000" vlink="#006000">
<font size="+4" color="#804040">
<strong><em>MUD-Dev<br>mailing list archive</em></strong>
</font>
<br>
[ <a href="../">Other Periods</a>
| <a href="../../">Other mailing lists</a>
| <a href="/search.php3">Search</a>
]
<br clear=all><hr>
<!--X-Body-Begin-->
<!--X-User-Header-->
<!--X-User-Header-End-->
<!--X-TopPNI-->
Date:
[ <a href="msg00102.html">Previous</a>
| <a href="msg00104.html">Next</a>
]
Thread:
[ <a href="msg00101.html">Previous</a>
| <a href="msg00106.html">Next</a>
]
Index:
[ <A HREF="author.html#00103">Author</A>
| <A HREF="#00103">Date</A>
| <A HREF="thread.html#00103">Thread</A>
]
<!--X-TopPNI-End-->
<!--X-MsgBody-->
<!--X-Subject-Header-Begin-->
<H1>Re: Unique id's</H1>
<HR>
<!--X-Subject-Header-End-->
<!--X-Head-of-Message-->
<UL>
<LI><em>To</em>: <<A HREF="mailto:mud-dev#null,net">mud-dev#null,net</A>></LI>
<LI><em>Subject</em>: Re: Unique id's</LI>
<LI><em>From</em>: <A HREF="mailto:coder#ibm,net">coder#ibm,net</A></LI>
<LI><em>Date</em>: Fri, 11 Apr 97 23:33:04 -0700</LI>
</UL>
<!--X-Head-of-Message-End-->
<!--X-Head-Body-Sep-Begin-->
<HR>
<!--X-Head-Body-Sep-End-->
<!--X-Body-of-Message-->
<PRE>
On 12/04/97 at 12:51 AM, "Jon A. Lambert" <jlsysinc#ix,netcom.com> said:
>> From: clawrenc#cup,hp.com
>> Yeah, but I figure that the date check for the ObjectID (time_T value
>> comparison of requested vs received objects) should pretty well trap
>> most of them.
>>
>Isn't it possible, especially in a multi-threaded system, to generate
>identical IDs if you depend on date/time stamps?
While possible in those loose terms, if your ObjectID allocation code is
thread-safe its not a problem. Its just a question of making sure that
you don't have a race conditions in your container updates/checks to get
the records# half of the ObjectID (which can be a problem depending on
your approaches). I brute forced the issue as I recall my putting a mutex
on the ObjectID allocation calls so while multiple ID's can be requested
simultaneously, the actual provision of ID's is serialised. After that it
was just a question of making sure that the period that the mutex is
locked for a call is kept to an absolute minimum.
Note: This gets messy if you go for a distributed database.
There's no problem if two ObjectID's contain the same timestamp. It
doesn't matter at all. What has to be unique is the combination of
record# and timestamp -- and that combo must be unique for the entire life
of the database. Happily this is not a problem until April 2038, longer
if you chose a different timestamp format.
>I'm currently
>generating IDs just like Cold, except I'm using a big int and never fill
>in the holes.
I used to use ColdX's format (stolen whole cloth from MOO): a 32bit
integer record# for the ObjectID which was a direct index into the DB for
the object. In running a couple early spoof/watcher/spawning mobile tests
I found I could easily wrap 2^32 created and destroyed objects in a week
or so. That wasn't good enough, and thus was born my current concept of
recycling and a 64bit time_t/Record# ObjectID. This leaves me with a
maximum of 2^32 (unsigned) simultaneous objects in the DB, which should be
enough.
I'm rather pleased actually -- the last time I had the server in a shape
it would actually run, I had it creating and destroying about 100,000
objects per hour while mobiles wandered about the game going in and out of
spoof/watcher areas, and breeding like crazy. It ran for a good 5 or 6
days before syslodg crashed when it ran out of disk space for its logs...
The DB grew by about 5% almost immediately to handle the "float" for the
extra Object ID's, and after that just stayed constant.
Figure, that's what, about 40+ million objects being created and
destroyed... Certainly not enough to cause a 32bit wrap, but a good
enough test to demonstrate that the idea works.
--
J C Lawrence Internet: claw#null,net
----------(*) Internet: coder#ibm,net
...Honourary Member of Clan McFud -- Teamer's Avenging Monolith...
</PRE>
<!--X-Body-of-Message-End-->
<!--X-MsgBody-End-->
<!--X-Follow-Ups-->
<HR>
<!--X-Follow-Ups-End-->
<!--X-References-->
<!--X-References-End-->
<!--X-BotPNI-->
<UL>
<LI>Prev by Date:
<STRONG><A HREF="msg00102.html">Re: Of disk swapping, database structure & project management..</A></STRONG>
</LI>
<LI>Next by Date:
<STRONG><A HREF="msg00104.html">Re: Yet Another Introduction</A></STRONG>
</LI>
<LI>Prev by thread:
<STRONG><A HREF="msg00101.html">Re: Unique id's</A></STRONG>
</LI>
<LI>Next by thread:
<STRONG><A HREF="msg00106.html">Re: Unique id's</A></STRONG>
</LI>
<LI>Index(es):
<UL>
<LI><A HREF="index.html#00103"><STRONG>Date</STRONG></A></LI>
<LI><A HREF="thread.html#00103"><STRONG>Thread</STRONG></A></LI>
</UL>
</LI>
</UL>
<!--X-BotPNI-End-->
<!--X-User-Footer-->
<!--X-User-Footer-End-->
<ul><li>Thread context:
<BLOCKQUOTE><UL>
<LI><strong><A NAME="00066" HREF="msg00066.html">Dupes are my fault (again)</A></strong>,
coder <a href="mailto:coder#ibm,net">coder#ibm,net</a>, Thu 10 Apr 1997, 12:08 GMT
<LI><strong><A NAME="00061" HREF="msg00061.html">Unique id's</A></strong>,
Chris Gray <a href="mailto:cg#ami-cg,GraySage.Edmonton.AB.CA">cg#ami-cg,GraySage.Edmonton.AB.CA</a>, Wed 09 Apr 1997, 21:46 GMT
<UL>
<li><Possible follow-up(s)><br>
<LI><strong><A NAME="00094" HREF="msg00094.html">Re: Unique id's</A></strong>,
clawrenc <a href="mailto:clawrenc#cup,hp.com">clawrenc#cup,hp.com</a>, Sat 12 Apr 1997, 06:03 GMT
</LI>
<LI><strong><A NAME="00101" HREF="msg00101.html">Re: Unique id's</A></strong>,
Jon A. Lambert <a href="mailto:jlsysinc#ix,netcom.com">jlsysinc#ix,netcom.com</a>, Sat 12 Apr 1997, 11:49 GMT
</LI>
<LI><strong><A NAME="00103" HREF="msg00103.html">Re: Unique id's</A></strong>,
coder <a href="mailto:coder#ibm,net">coder#ibm,net</a>, Sat 12 Apr 1997, 13:55 GMT
</LI>
<LI><strong><A NAME="00106" HREF="msg00106.html">Re: Unique id's</A></strong>,
Jon A. Lambert <a href="mailto:jlsysinc#ix,netcom.com">jlsysinc#ix,netcom.com</a>, Sat 12 Apr 1997, 23:53 GMT
</LI>
<LI><strong><A NAME="00119" HREF="msg00119.html">Re: Unique id's</A></strong>,
coder <a href="mailto:coder#ibm,net">coder#ibm,net</a>, Mon 14 Apr 1997, 00:01 GMT
</LI>
<LI><strong><A NAME="00122" HREF="msg00122.html">Re: Unique id's</A></strong>,
Jeff Kesselman <a href="mailto:jeffk#tenetwork,com">jeffk#tenetwork,com</a>, Mon 14 Apr 1997, 02:40 GMT
</LI>
<LI><strong><A NAME="00123" HREF="msg00123.html">Re: Unique id's</A></strong>,
Jon A. Lambert <a href="mailto:jlsysinc#ix,netcom.com">jlsysinc#ix,netcom.com</a>, Mon 14 Apr 1997, 04:31 GMT
</LI>
</UL>
</LI>
</UL></BLOCKQUOTE>
</ul>
<hr>
<center>
[ <a href="../">Other Periods</a>
| <a href="../../">Other mailing lists</a>
| <a href="/search.php3">Search</a>
]
</center>
<hr>
</body>
</html>