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Dang! What to do about filtered indexes

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    #1

    Dang! What to do about filtered indexes

    Now I discover that filtered indexes in tables are unreliable. should I be shivering in my boots? I have a number of filtered indexes in my app and now I sit in fear of a crash or something. What can I do to head off impending doom?

    Does anyone know if this problem will disappear in Version 5?
    Tags: None
    #2
    RE: Dang! What to do about filtered indexes

    hi greg:

    although this has been discussed many times, i'm still using 4.03 build 230 which seems to crash the index after 8 lookups. in searching this thread i couls find no real fix.

    what i thought i might try is using a dummy table placing the already filtered records from the real table and then using the dummy table for lookup with no filters. has anyone tried this approach? (don't want to waste my time if it is already proven not to work)

    i tried running a filtered query on the real table prior to it being used as a lookup, however it displayed all records so it didn't work.

    any help much appreciated!!

    regards,

    ed

    Comment

      #3
      RE: Dang! What to do about filtered indexes

      Ed,

      You and Greg may be talking about different things.

      When an index is defined for a table, Alpha Five lets you embed a filter expression in it. This becomes a filtered index. The effect will be to limit the display of records in the current table to those which meet the index filter criteria.

      When a table lookup field rule is defined, Alpha Five lets you embed a filter expression in the field rule, narrowing the range of records that will be presented in the lookup dialog. This is a filtered table lookup field rule (or filtered lookup for short).

      It sounds like Greg is asking about the former, and you may be talking about latter.

      -- tom

      Comment

        #4
        RE: Dang! What to do about filtered indexes

        hi tom:

        even though it was clearly stated in greg's text i glossed over it completely.

        i'll start a new thread (on an old topic).

        thanks,

        ed

        Comment

          #5
          RE: Dang! What to do about filtered indexes

          Greg,

          There are filters and there are filters. If your system has been in use for a while and problems are not being experienced you can breathe easier. But stick a note in your journal to remind you to check this if a problem manifests itself.

          On the other hand I would immediately begin thinking about a redesign, if a filter expression relies on values that must be retrieved from sources outside the current record. For example, if the filter relies on a variable, or uses functions like lookup() to retreive values from external tables, or the like.

          -- tom

          Comment

            #6
            RE: Dang! What to do about filtered indexes

            Hi gents,

            "There are filters and there are filters."

            This must be so, because I filter lookups without incident. But as Tom says, no fancy stuff unless using a global variable counts as fancy. I filter by department number (e.g. "D30") which is a field of every record and is also established as a global by the user's logon. I want users to only see records from their own department.

            I declare the variable in table definition so the field rule always sees it.

            It just works. Period.

            Bill
            Bill Hanigsberg

            Comment

              #7
              RE: Dang! What to do about filtered indexes

              I agree on the global variables, Bill. I don't use them much, but there are a couple of instances. I still have one index that gets dropped regularly and cannot determine why, but that one uses only a standard text field with no filter in its index. Baffles me.

              Tom Lyon

              Comment

                #8
                RE: Dang! What to do about filtered indexes

                I use variables in many cases, but my system is entirely driven by menu screens containing buttons with pre-defined scenarios. The variable is set only when the button is pushed, then the form uses that variable to filter itself. Two things I like about that is 1.) indexes are kept to a minimum and 2. if someone gets to the control panel the forms cannot be opened directly since they are a based upon a variable that is non-existent because the menu didn't call it.

                I too have had indexes disappear which renders many functions inoperable. This method has reduced those errors quite a bit.

                Comment

                  #9
                  RE: Dang! What to do about filtered indexes

                  Tom,

                  You might check to see if your users have managed to store punctuation symbols in the text field. In some rare cases I've found that this can cause trouble, including failed indexes. -- tom

                  Comment

                    #10
                    RE: Dang! What to do about filtered indexes

                    Greg,

                    Any discussion of filtered indexes should include a mention of Ira Perlow's suggestion concerning LQO (Lightning Query Optimization). In many instances LQO will cause a new query to use a permanent index list, instead of building a new query list from scratch. This is discussed in Ch 3 of the User's Guide.

                    Anyway, Ira's idea is to embed in each index key a prefix which can be used later in a query. This neatly permits one to use the query without a performance penalty, AND without having to use a filtered index.

                    -- tom

                    Comment

                      #11
                      RE: Dang! What to do about filtered indexes

                      I should mention that Tom brought up a good point. The method I use does pose a performance penalty (a few seconds to build to the index), however I have about 40 people using this at one time. To lose an index requires me to call each of the affected users, ask them to logout, and recreate the indexes, since it has to be in exclusive mode. For my instance I would rather have a more stable method with a peformance penalty. Each developers circumstances are different, I try to create apps that when errors occur, I do not need to be in exclusive mode to fix it. With as many users as I have, I need to keep the app consistent with very few user interruptions due to errors.

                      Comment

                        #12
                        RE: Dang! What to do about filtered indexes

                        Thanks Tom for the insight. I think I MAY be safe since my filtered indexes are based on an actual value in the record. I have a field called "Active" and the index only includes records that have a .t. value in the field.

                        However I do use filtered lookups and I will investigate the options available.

                        Comment

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