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

Bernard Lebel 3dbernard at gmail.com
Wed Jan 18 21:14:45 CET 2006


Strange, I have just found out that all queries past the first one
always behave the same way: they return the very first result.
Somehow, the program seems to keep in memory the query results.


I hope people don't mind if I'm doing the confessional way of
debugging, but I've been knocking my head on that for almost 3 full
days :-(


Bernard




On 1/18/06, Bernard Lebel <3dbernard at gmail.com> wrote:
> Btw I have tried running much simpler versions of the query, like
> "SELECT * FROM TB_CURRENT_JOBS WHERE Status = 'Pending'", but yet
> again I get the same results. *sigh*
>
>
> Bernard
>
>
>
> On 1/18/06, Bernard Lebel <3dbernard at gmail.com> wrote:
> > 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
> > >
> >
>



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