hi,
maybe it would be simpler and faster to mantain a locked list in memory
with threads and downloading url.
then, before download, you must check for existing download in list.

> -----Original Message-----
> From: PUB: Matteo Giacomazzi [mailto:matteo.giacomazzi@...]
> Sent: Viernes, 05 de Julio de 2002 12:16
> To: ib-support@yahoogroups.com
> Subject: [ib-support] Serialization?
>
>
> Hi all,
>
> as I stated before, I'm writing my graduation thesis.
> Part of my thesis requires I realize a kind of "crawler", that is a
> "robot" that discover and retrieve documents from a network. This
> robot keeps the URL that finds in the documents in a Firebird DB.
>
> Due to netiquette policy, I want that if one thread is downloading a
> document from a host, no other thread should download documents from
> the same host.
>
> HOST is a separate table, so I can "mark" a row as "downloading"
> when assigned to a task and then mark it as "free" when the download
> process ends.
>
> Now the problem: let's imagine that two threads request a URL at the
> same time.
> 1. How can I avoid they get the same URL?
> 2. How can I avoid they get two different URLs lying on the same
> HOST?
>
> I guess that the problem should be easily solved if there would be a
> kind of "serialization" in DB queries.
> I know that a real DBMS should be able to perform queries as if they
> were serialized but... how can I explain it to my Firebird?
> There should be a trick I cannot see...
>
> Thank you in advance and sorry for the long post!
>
> Kind regards,
> --
> Matteo
>
> mailto:matteo.giacomazzi@...
> ICQ# 24075529
>
>
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