Strange locking behaviour

I am running 7.2 on FreeBSD-current.  I have an web page that I have been
playing with for tracking stocks online.  It has a table which contains
all of my calculations.  Once a day I pull down a report from MarketWatch
of all stocks that meet a criterion I have defined.  Once every 5 minutes
I download new stock data, and compute buy/sell recommendations. Anyway,
that is all working.  Now for my problem:

I download my list from MarketWatch and then go and pull historical
data for all the new stocks in the list.  The program that gets the
historical data does:

BEGIN WORK ;
SELECT stockid FROM stocks WHERE ticker = 'M$FT' FOR UPDATE ;
UPDATE stocks SET nextupdate = NOW + INTERVAL '1 DAY' ;
....Insert 7 years of stock data....
UPDATE stocks SET nextupdate = NOW() ;
COMMIT WORK ;

The program that gets the 5 minute updates does:

SELECT stockid FROM stocks WHERE nextupdate <= NOW() ;
-- and for each stockid it finds above
BEGIN WORK ;
....Insert new data...
COMMIT WORK ;

Looks simple enough, right?

Anyway, while the historical data INSERTs are occurring, no other
application can insert data into any of my tables, so my 5 minute update
sits there and diddles around forever, and I don't get recommendations.
My understanding from reading the docs is that 'FOR UPDATE' gets a 'ROW
SHARE' lock, and updates and inserts get a 'ROW EXCLUSIVE' lock.  I cannot
understand why all my apps, except the historical data app, are showing
'waiting' in a 'ps' command.  Is the problem that after I do the fist
"UPDATE" command it promotes the lock to 'ROW EXCLUSIVE', and then the 5
minute update cannot even look at the value of 'nextupdate' until after
the inserts have completed?  I set 'nextupdate' to tomorrow specifically
to prevent the 5 minute update from doing anything until the historical
data is available.

Any ideas?

- brian


Wm. Brian McCane                    | Life is full of doors that won't open
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