On Sat, 1 Jan 2011, Mark Morgan Lloyd wrote:
Michael Van Canneyt wrote:
On Fri, 31 Dec 2010, Mark Morgan Lloyd wrote:
I've just taken our name server down for maintenance, and noted that a
db-aware app I'd left running ground to a halt despite the fact that it
was only activating queries, not establishing new (named) connections.
The connection was being made by host name rather than by dotted-quad
address, resulting in a long-term handle associated with the TPQConnection
object. Whenever a TSQLQuery is activated, it results in the opening of a
short-term handle, if I'm reading things correctly associated with a
TSQLTransaction object which relies on the host information from the
connection object.
My expectation is that these short-term handles should not mandate a name
lookup, since the host name or address cannot be specified at this point.
Am I being unreasonable?
In order to support multiple transaction, a connection is created for each
transaction. So if you application creates transactions at regular
intervals, then it will perform a name lookup each time a transaction is
created.
The program is not creating explicit transactions and only has read access to
the table. I'm establishing a connection during program initialisation and
then alternating between two query objects, it's the activation of the query
object which is causing a short-term handle to be opened.
Please excuse me for not having looked at the sources yet, but I presume that
the client library is performing a name lookup if the initial connection was
by name (hopefully it doesn't do this if the connection was by address). I'd
suggest that the IP address could usefully be cached in case of name server
failure, in the same way that other parameters are cached somewhere (for
example, the password in the connection object can be wiped without affecting
operation).
The name lookup is not done by FPC itself, but by the Postgresql client library.
This is outside of FPC's control; FPC just asks a connection on a certain IP
address, it doesn't even know if the adress is an actual IP addres or a DNS name.
You can always do the address lookup yourself, if you want, and pass that to the
connection component.
Michael.
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