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index corruption

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    #1

    index corruption

    looking for help, hope someone out there can help me. i used to talk with tom cone jr. about the problems that i had with alpha reguarding heap locks, i'm having trouble now with the indexes continiuosly getting corrupted so much that it's taking too much time out of our workday just to rebuild our indexes. it is starting to behave the same way it did right before the entire system crashed early last month. are there any patches that will help the alpha system from having these problems? thanks, Gary Hummingbird
    Tags: None
    #2
    RE: index corruption

    Gary

    This is a topic that has been visited many many times. Here is a link to just one of the threads.

    http://msgboard.alphasoftware.com/alphaphorum/read.php3?sortby=lastreply&direction=desc&num=11&id=66052&thread=65803

    The first question is what is happening to the index? Is it being deleted, or just corrupted? Is this occuring on a network?

    Indexes will be deleted if the index expression can't be evaluated. This can happen if there is bad data in the table field that is included in the index, or a variable is used in the expression.

    Corrupted indexes are frequently caused by filters in the index or indexes being locked when a record is being updated. I have an application that has the second problem. The cause is having the same table linked more than once in the same set with a different filter for each link. The child table then is edited using xbasic. Since the set link index is effectively locked when the record changes in xbasic, it sometimes doesn't update, causing a corrupted index. the same can occur if the table is linked more than once with different expressions.

    Because of some requirements from the end user, it is not realistically possible to completely elminate the problem in my case. So I include index updating and rebuilding code for the user. If the indexes appear corrupted, they run the maintenance and clean up the problem. Not an ideal solution, but the corruption occurs rarely, maybe once or twice a year.

    Another cause of what appears to be corrupted indexes is the practice of using long names for fields or indexes. Since the native dbf format only recognizes 10 characters in the names, if you use long names Alpha modifies the actual name and saves the long name in the table data dictionary with a pointer back to the actual name. If this link becomes damaged, the index fails since it can't identify the real field or index names.

    If the problem is happening on a networked application, there have been a number of threads on "opportunistic locking". This apparently causes indexes to get corrupted. Just search for "opportunistic locking" in quotes and you should get a bunch of hits.

    Most people have very few problems with indexes if they follow a few simple rules. Keep all field and index names to 10 characters of less. Avoid filters and complex expressions in the index definition. Compact the database whenever you make any design changes. This reduces the chance of the data dictionaries becoming corrupted. Sometimes corruption there appears as an index problem if long names are used. Include some maintenance option to update indexes if the rest of the precautions fail.

    There is no update for A5 that solves the problem. You should be sure to have the newest update for your version, but indexes are typically very stable. I have a number of applications that have run for years were the indexes have never been updated - ever.

    Jerry

    Comment

      #3
      RE: index corruption

      Gary,

      If you're staying with vers 4 of Alpha Five, I strongly recommend you at least upgrade to vers 4.5.

      In addition to Jerry's advice, there are some other things you should do if you are running with Win2000 or XP on the server or workstations. By default these systems are tuned for Microsoft's client-server databases. They need to be "de-tuned" for Alpha's file-sharing approach.

      -- t

      Comment

        #4
        RE: index corruption

        Tom, We are using Alpha 4.5, but one workstation has Windows 98 while the other workstation has Windows XP on it. It almost seems as though when the workstation with XP gets used while the other workstation is up, the indexes get corrupted. Sometimes they disappear, other times they just say that they have been corrupted. We have 5 workstations that run on Windows XP & 2 workstations that are running on Windows 98SE. Any clues???? Thanks....

        Comment

          #5
          RE: index corruption

          also, it seems strange, but my boss pointed out to me that it never has corrupted indexs when he or myself uses these 2 workstations. everybody else at this company with the exception of the accounts manager has this problem. I read in one post about index corruption being a timing issue... could that be my major problem to start with????? Thanks, Gary

          Comment

            #6
            RE: index corruption

            Gary

            Since some users have the problem and others don't, you may want to watch what the others users are doing. Sometimes users inadvertently do something they shouldn't. A classic is opening an form based on a complex set with referential integrity turned on in the set, and then walking away from the computer with a record in edit mode, which may lock the tables. Someone else edits a record in one of the child tables, and you could have an index problem.

            I have a program that only gave a error for one user. I finally wrote a routine to trap a rolling 20 actions and key strokes. When an error occured, there was a log file generated. When I took the output and duplicated their actions, I was shocked. They were doing something that was really odd, but made sense to them. It was something neither I or the other users would have dreamed of trying. I had to rewrite part of the application to prevent them from going where they were going. The errors stopped.

            Jerry

            Comment

              #7
              RE: index corruption

              Thanks alot Jerry, that explains alot..... Gary

              Comment

                #8
                RE: index corruption

                Just curious,

                How do you de-tune Microsoft's Client Server databases?

                By default these systems are tuned for Microsoft's client-server databases. They need to be "de-tuned" for Alpha's file-sharing approach

                Comment

                  #9
                  RE: index corruption

                  Search for threads discussing

                  opportunistic locking

                  -- t

                  Comment

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