From: Marcus Bointon
Date: September 12 2010 7:21pm
Subject: Re: Unique ID's across multiple databases
List-Archive: http://lists.mysql.com/replication/1941
Message-Id: <836C2727-36A6-4C5C-8308-21FFB20C9507@synchromedia.co.uk>
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On 12 Sep 2010, at 19:47, Kiss D=E1niel wrote:

> - SID adds only 2 bytes in this case to the size of the primary key =
item.
>   It can be even 1 byte if I'm sure I'll never exceed maximum 255 =
servers. But
>   anyhow, it is still way smaller than the 16 byte of a UUID field, =
even if
>   using BIGINT's.

You can maintain your own sequence tables a la postgres if you use =
transactions to ensure atomicity, though that doesn't help across =
databases (I suspect the same is true in postgres).

FWIW my auto_increment_offset value is usually the same as my server ID. =
auto_increment_increment also reduces the number of usable values for =
integer keys too; e.g if it's 10, you've reduced your key space by a =
factor of 10 too, meaning you may need to use bigints if you potentially =
have more than 400m records in any given table.

One small observation that I've seen work is to use binary fields for =
UUIDs and always wrap access to them in hex/unhex functions. You halve =
your storage requirements for the same amount of data that way.

Marcus=

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