Re: howto implement a fifo queue in MySQL Cluster ?

[Martin Skold]

Hi!

Autoincrement values are inserted in order, but we prefetch
series of values to get better performance. So if you are
inserting from several connections (or mysqld's) you will
not get a total ordering. If you want that you can set
ndb_autoincrement_prefetch_sz to 1 should force order.
This will, however, degrade performance for inserts.

BR
-- Martin
Hendrik Woltersdorf wrote:
> Hi all,
> 
> how do I implement a fifo queue in MySQL Cluster ?
> 
> What I want to do:
> 
> I write inserts and updates to some tables with triggers into a queue.
> These rows have to be read and processed in chronological order.
> My first attempt was to use a table with an autoincrement column as the
> primary key. But tests show, that these autoincrement values are not
> inserted in chronological order. A datetime column does not help either,
> because it is by far not precise enough, and it depends on the
> synchronization of the clocks of the different sql node machines.
> 
> Any ideas, how to read these data rows in chronological order ?
> 
> The second best idea is, to use "select max(PK)+1", but this will cause
> lots of duplicate key errors.
> 
> I am using MySQL Cluster version 7.0.7 with 2 data nodes, 2 management
> nodes and 2 sql nodes.
> 
> kind regards
> 
> Hendrik Woltersdorf
> XCOM AG
> Tel.: [phone]
> Tel. mobil: 0178/5710078
> Email: Hendrik.Woltersdorf@stripped
> 
> 
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