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  • From: Frediano Ziglio <freddy77 AT gmail.com>
  • To: esterniclos AT gmail.com, FreeTDS Development Group <freetds AT lists.ibiblio.org>
  • Subject: Re: [freetds] SQL Cluster always on
  • Date: Sat, 13 Feb 2016 08:55:54 +0000

2016-01-07 9:31 GMT+00:00 esterniclos AT gmail.com <esterniclos AT gmail.com>:
> Hello everyone,
>
> We would like to adapt freetds to SQL Server Always On Clustering.
>
> This kind of cluster is pretty simple:
>
>
> Every database has associated a Listener with a dns name. E.g.
> dblistener.myorg.com
>
> Every listener has 2 or more IPs associated:
> nslookup dblistener.myorg.com responds something like: 10.57.3.2
> and 10.57.4.52
>
>
> Only one of the IP's serves the database (active-passive)
>
> The connection has to be made directly to the listener. and use
> the IP that is working at that moment.
>
> TDS Behaviour at this point.
>
> Right now, TDS works as long as the listener is in the first node.
> In the example
> dblistener.myorg.com instance working in 10.57.3.2
>
> If the database is moved to another instance, it returns a timeout.
> Never checks the rest of IPs
>
> Possible solution
>
> Try to login in several times with as many objects as IP's are
> in DNS:
>
> tds/login.c:tds_set_host(TDSLOGIN * tds_login,
> const char *hostname)
>
>
> This would penalize a little when the database is in the
> backup instance, as it has to receive a timeout before making the
> connection.
>
> To speed up things, the last IP where the database was seen
> could be also stored, and only ask dns if there is a time out.
>
> Thank you for your time, and any advice is welcome.
>
> Ester Niclós Ferreras


Now (master) we try to connect to all IPs, not just the first.
Yes, could be cached the last success somewhere but is a start.

Frediano



  • Re: [freetds] SQL Cluster always on, Frediano Ziglio, 02/13/2016

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