MySQLdb - Query/fetch don't return result when it *theorically* should

[Bernard Lebel]

Oops, sorry: link to sources
http://www.bernardlebel.com/scripts/nonxsi/help/


Thanks again
Bernard



On 1/18/06, Bernard Lebel <3dbernard at gmail.com> wrote:
> Hello,
>
> I'm stumbled at a serious problem, and quite frankly getting
> desparate. This is a rather long-winded one so I'll try to get
> straight to the point.
>
> I have this Python program, that performs MySQL queries to a database.
> These queries are performed at regular intervals. Basically it is
> looking for fields that match certain criterias. Such fields are not
> present at all time. When the program finds such field, it then takes
> an action, if nothing is found, just keep this query-fetch cycle
> forever.
>
> I don't know where the source of the problem is, but the symptoms go as follow:
>
> When the program starts, the first time it performs a certain
> query/fetch, a result is fetched. Now, later on, when the action done
> after the first fetched is completed, the program starts
> querying/fetching again. But it seems unable to the fetch anything
> else with the same query.
>
> If an entry that the query should return is inserted in the database,
> the program just can't get it once it has started.
>
> A more schematic representation of the symptoms.
>
> What it should do:
> 1. program starts
> 2. enter query-fetch cycle
> 3. find specific entry, take action
> 4. action done
> 5. resume query-fetch cycle
> 6. find specific entry, take action
> 7. action done
> 8. resume query-fetch cyle
> 9. there was nothing to be found, continue cycle
> 10. find specific entry, take action
> 11. action done
> 12. resume query-fetch cycle...........
>
> What it does now:
> 1. program starts
> 2. enter query-fetch cycle
> 3. find specific entry, take action
> 4. action done
> 5. resume query-fetch cycle
> 6. no more entry fetched despite valid entries being in the database
>
> What is does now also:
> 1. program starts
> 2. enter query-fetch cycle
> 3. there was nothing to be found, continue cycle
> 4. valid entry added my myself, manually, and successfully committed
> 5. query-cycle continues, entry just added never found.......
>
> I have looked at connection objects, cursor objects, and I just can't
> seem to find the cause of that behavior.
>
> In parallel, if I run individual queries in a command line shell, I
> fetch the entries as expected.
> The only way I have found to force the program to find the new entry,
> is to close the connection and create a new one, every time it
> performs a transaction. Not very efficient.
>
>
>
> To give a little more details about the implementation.... when the
> program starts, it starts a little queue server in a separate thread.
> This queue server is nothing more than a list. Each time a query has
> to be performed, it is added to the queue.
> The queue server checks the queue to find if it has something to do.
>
> When if finds something, it carries the entire operation, from query
> to fetch/commit. It then stores the result in a dictionary, using a
> unique ID as the key. At that point, the list element is removed from
> it.
>
> The function that submitted the query to the queue, during that times,
> checks the dictionary until the result of the operation shows up, and
> then checks the actual result. The result is then returned to the
> original function who submitted a database transaction.
>
>
>
> I don't know what other details to provide, other than the sources
> themselves.......
> farmclient_2.0_beta05.py is the top program file
> The other py files are the imported modules
> - fcSql is the actual database transaction management module
> - fcJob has a function called readyGetJob(), wich is at the origin of
> the MySQL query. The actual query being used is located on line 202.
> The sql file is used to create the database
>
> Thanks for any help, let me know if you need more details
>
> Bernard
>