FWD » Core Development » Database

def var i as int.
def var n as int init 30.
def buffer b1 for book.

do transaction:
   for each book:
     delete book.
   end.

   do i = 1 to n: // to have multiple progressive brackets...
      create book.
      assign 
         book.isbn = string(i)
         book.book-id = i
         book.book-title = string(i).
      release book.
   end.

   for each customer: delete customer. end.
   create customer.
   customer.customer = 1.
   release customer.
end.

for each book no-lock:
   // message book.isbn.

   if book.book-id = 11 then 
   do transaction:
      find first customer exclusive-lock.
      customer.customer = customer - 1.
      release customer.

      find b1 where b1.book-id = book.book-id no-error.
      if avail b1 then do:
         b1.book-id = b1.book-id * -1.
         b1.isbn = b1.isbn + "foo".
      end.
   end.
end.

Is an example that can reproduce the issue with FWD 15680. With later versions, the for each doesn't generate ProgressiveResults, so this test doesn't reproduce anymore. The FOR EACH should be replaced with an OPEN QUERY:

def var i as int.
def var n as int init 30.
def buffer b1 for book.

do transaction:
   for each book:
     delete book.
   end.

   do i = 1 to n: // to have multiple progressive brackets...
      create book.
      assign 
         book.isbn = string(i)
         book.book-id = i
         book.book-title = string(i).
      release book.
   end.

   for each customer: delete customer. end.
   create customer.
   customer.customer = 1.
   release customer.
end.

open query q for each book no-lock.
get first q.
get next q.
get next q.
get next q.
get next q.
get next q.
get next q.
get next q.
get next q.
get next q.
get next q.

do transaction:
   find first customer exclusive-lock.
   customer.customer = customer - 1.
   release customer.

   find b1 where b1.book-id = book.book-id no-error.
   if avail b1 then do:
      b1.book-id = b1.book-id * -1.
      b1.isbn = b1.isbn + "foo".
   end.
end.

get next q.

The goal is to make the edge record "disappear" without invalidating the query so that ProgressiveResults will no longer match the last record from the bracket with the first record of the next bracket. The invalidation leads to a bad state of the query.

I don't really understand the fix.

The line Results cached = cacheResults(old, true); where Results old = adapter.getResults(); will iterate (and consume) all the records in the adapter. Now, if we are not in preselect mode, we assume caching the results made the query go into dynamic mode.

But, the condition to enter this block is if (cacheOnReval || isPreselect()) - so, can the preselect be false, when entering this code?

Also, even so, what happens with the adapter's results if 'went into dynamic mode'?

But, the condition to enter this block is if (cacheOnReval || isPreselect()) - so, can the preselect be false, when entering this code?

It becomes false when calling cacheResults. In the process of iterating all results, we detect a mismatch in order so the query is invalidated. At that point, null is returned by ProgressiveResults simulating an "QueryOffEnd" and Results cached will contain only some records until the invalidation occurred.

Also, even so, what happens with the adapter's results if 'went into dynamic mode'?

It stays null because invalidation triggered AdaptiveQuery.resetResults, making results null and the adapter disconnected.

Motivation: The original problem was that the results were made null, but the adapter was set to the inconsistent Results cached. This is an invalid state. The adapter should have stayed disconnected in order to pick up a new results.

Can we rely on errorCondition instead of !isPreselect()? That's set like this:

AdaptiveQuery.resultsChanged() line: 2603    
ProgressiveResults.fireResultsChanged(boolean) line: 1387    
ProgressiveResults.fireResultsChanged() line: 1366    
ProgressiveResults.getResults(ProgressiveResults$Locator) line: 1294    
ProgressiveResults.moveTo(int, boolean) line: 1077    
ProgressiveResults.moveTo(int) line: 925    
ProgressiveResults.next() line: 483    
AdaptiveQuery(PreselectQuery).cacheResults(Results, boolean) line: 5977    
AdaptiveQuery.sessionEvent(SessionListener$Event) line: 2308    
Persistence$Context.notifySessionEvent(SessionListener$Event) line: 6234    
Persistence$Context.commit() line: 5607    

Yes, this is what is happening in next. Would you prefer errorCondition? I guess it is less confusing than seeing isPreselect and then right after !isPreselect conditions.

Alexandru Lungu wrote:

Would you prefer errorCondition? I guess it is less confusing than seeing isPreselect and then right after !isPreselect conditions.

Yes, is more explicit that we do not cache because something happened while trying to cache.

Committed 9853a/15839 and 15840, replacing !isPreselect with errorCondition. Please review.

Alexandru Lungu wrote:

Committed 9853a/15839 and 15840, replacing !isPreselect with errorCondition. Please review.

I'm OK with the change.

Also can confirm that #9777 is fixed.