[OSM-dev] Alternative PostgreSQL Schema
tom at compton.nu
Wed Oct 24 15:31:24 BST 2007
In message <471F5573.6060005 at bretth.com>
Brett Henderson <brett at bretth.com> wrote:
> Tom Hughes wrote:
>> There's also a question of how to handle version number allocation - we
>> currently rely on an obscure feature of MyISAM tables to do it...
> That's something else I was curious about. I had assumed that this was
> being done in code. In other words using a sequence to allocate the
> main id then incrementing in code with any concurrent edits resulting in
> a key violation.
Nope - the version number is an auto increment column. See:
In particular the bit about MyISAM and auto increment fields which
are secondary index columns:
"For MyISAM tables you can specify AUTO_INCREMENT on a secondary
column in a multiple-column index. In this case, the generated
value for the AUTO_INCREMENT column is calculated as
MAX(auto_increment_column) + 1 WHERE prefix=given-prefix. This is
useful when you want to put data into ordered groups.
Tom Hughes (tom at compton.nu)
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