Webware for Python

Has there been any discussion of using the DB-SIG's DB-API spec as a basis
for abstracting support for new databases?



-----Original Message-----
From: Steve Waterbury [mailto:steve.waterbury@...]
Sent: Saturday, March 02, 2002 1:27 PM
To: webware-discuss@...
Subject: [Webware-discuss] Re: MiddleKit questions?


Jason Hildebrand wrote:

> FYI: I think there may be (at least the beginnings of) a PostgreSQL
> adapter floating around.  Someone else can probably send it to you if
> you're interested.

I would be very interested!  I am about to begin developing one, 
if there isn't one.  If anyone else is working on one, please 
speak up ... I'd be happy to help!  

Cheers,
-- Steve.

Stephen C. Waterbury                          
Code 562, NASA/GSFC

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Tripp: Thanks very much for the tip about locking the connection while in
use. That seems to have cleared up the segmentation faulting. I've got a lot
to learn ...

Now I'm seeing a large percentage of the benchmarker requests returning no
data, and I'm pretty sure that'll be fixed by closing and reopening the
connection in the try/finally block as you suggested.

I appreciate the help.

Cheers!
--
David Hancock | dhancock@... | 410-266-4384


-----Original Message-----
From: Tripp Lilley [mailto:tlilley@...] 
Sent: Saturday, March 02, 2002 3:15 PM
To: Hancock, David (DHANCOCK)
Cc: 'webware-discuss@...'
Subject: Re: [Webware-discuss] WebKit seg-faulting when connecting to Oracle


On Sat, 2 Mar 2002, Hancock, David (DHANCOCK) wrote:

> (Apache benchmarker) and have it make a couple thousand requests, with 
> 10-40 concurrent.  With only a couple concurrent requests, no 
> problems. With 10 or more, I get a seg fault pretty quickly.

I have no Oracle experience, but I'm going to go out on a limb and guess
that the driver you're using isn't thread-safe, or isn't being used by the
Python wrappers in a thread-safe manner.

Just off the top of my head, I'd create a per-connection wrapper object that
uses a reentrant lock (see threading.RLock) to lock access to each
connection.

(more comments follow code snippet)

> 	class dhPage(ExamplePage):
> 	    import DCOracle2
> 	    dbconn = DCOracle2.connect('scott/tiger@...')
>
> 	    def writeBody(self):
> 	        self.write('<h3>select * from emp results</h3>')
> 	        res = dhPage.dbconn.execute('select * from emp')
> 	        list = dhPage.dbconn.fetchall()

Yeah, I'm pretty sure you're running into a thread-safety issue here. I'm
willing to bet that the connection object is barfing all over itself when
you end up with multiple threads running queries and trying to fetch their
result sets.

Here's a really cheesy rewrite:

class SafeConnection:
	import DCOracle2
	import threading.RLock as RLock

	def __init__ (self, init):
		self._conn = DCOracle2.connect(init)
		self._lock = RLock()

	def lock (self):
		self._lock.acquire()

	def unlock (self):
		self._lock.release()

	def doquery (self, query):
		results = []
		self.lock()
		try:
			self._conn.execute(query)
			results = self._conn.fetchall()
		finally:
			## this finally / unlock is very important
			## to make sure that other requests don't hang
			## if the query or something barfs.

			## You might want to harden it a bit more by
			## catching the exception and possibly closing /
			## reopening the connection.

			self.unlock()
		return results


class dhPage(ExamplePage):
	def __init__ (self):
		ExamplePage.__init__(self)
		self._conn = SafeConnection('scott/tiger@...')

	def writeBody (self):
		res = self._conn.doquery('select * from emp')
		# ... etc.


Of course, you don't -have- to break the connection and lock out into a
separate object, but if you -do-, then you'll have an easier time putting
this into a pool later.

Rendering more than one form in one page works. So I have two forms now on
one page. Their names are "FormOne" and "FormTwo".

Now, when I press a button on one of those two forms, _processForm() fails:

Traceback (most recent call last):
  File ".\WebKit\Application.py", line 387, in dispatchRequest
    self.handleGoodURL(transaction)
  File ".\WebKit\Application.py", line 535, in handleGoodURL
    self.respond(transaction)
  File ".\WebKit\Application.py", line 711, in respond
    transaction.respond()
  File ".\WebKit\Transaction.py", line 93, in respond
    self._servlet.respond(self)
  File ".\WebKit\HTTPServlet.py", line 37, in respond
    method(trans)
  File "D:\Webware\WebKit\ExTract\Template.py", line 47, in respondToPost
    Page.respondToPost(self, transaction)
  File ".\WebKit\Page.py", line 38, in respondToPost
    self._respond(transaction)
  File ".\WebKit\Page.py", line 67, in _respond
    self.writeHTML()
  File ".\WebKit\Page.py", line 129, in writeHTML
    self.writeBody()
  File ".\WebKit\Page.py", line 190, in writeBody
    self.writeBodyParts()
  File "D:\Webware\WebKit\ExTract\Template.py", line 150, in writeBodyParts
    self.writeContent()
  File "D:\Webware\FunFormKit\Form.py", line 138, in _processForm
    currentForm = self._formDefinitions[req.field('_formID_')]
TypeError: unhashable type


The line causing this is
currentForm = self._formDefinitions[req.field('_formID_')]

When I check what's used as the key, I see that req.field('_formID_')
returns
["FormOne", "FormTwo"].

I guess it should return one of those strings and not a list of them. Any
hint, what I did wrong?


Best regards
Franz GEIGER



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