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Data missing/corrupt

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  • Data missing/corrupt

    I am using A5v4 to run an application that is comprised of 15 - 20 tables, some of which have 650,000 - 700,000 records. I have encountered a problem several times over the course of the past few months (probably 4 times in three months) with one of the larger tables. When the problem happens, the last several thousand records in the table appear (when viewed in the default browse) to be blank. (We are alerted to this condition when an auto-increment id field starts over at 0 with strange results.)

    I have found that if I copy the 5 files that make up the table (.dbf, .ddd, .ddm, .fpt, .cdx) to another location (i.e. my C:) that I can view and work with the data normally. Further if I copy the copy that I have just made back to the server where the application is located, the data acts ok.

    Operating on the assumption that there was something wrong with the server that the data was located on, I have changed to a physically different server, but the problem has occured again in the new location.

    Has anyone else seen anything like this, or could anyone offer any suggestion? Thanks in advance,

    -Bill

  • #2
    RE: Data missing/corrupt

    Bill,

    The data was obviously there. If not, how could it have shown up on your machine? But if it was there (on the server) but invisible, that that suggests indexes.

    Hence, I ask, did you compact on the server. Did you rebuild indexes?

    Bill
    Bill Hanigsberg

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    • #3
      RE: Data missing/corrupt

      Bill:

      Thanks for the reply. I agree, the data was there, just not viewable (to me or A5 - hence the auto increment failure. You are right, it is probably an index corruption, not data corruption.

      I was unable to rebuild the indexes on the original copy of the table (on the server). When I tried, the index definitions disappeared.

      The local copy of the table updated just fine. I used the .cdx file (and all others - i.e. .ddd, .ddm, .ddx, .fpt) from the original (server) copy with out making any changes. The local copy, when copied back down to the server (after re-naming the original), works fine with the rest of the tables in the app.

      Although I have been able to fix the problem each time, this has happened to me 4 times in the last 3 months - and had not ever happened in the previous 6 years of using Alpha. So I am concerned.

      We have not done regular database compacts on our app, and this may be the problem. It is unfortunately not possible to run a database compact directly on our app, as it takes too long on the server based copy (most of a day). We have found though that we can copy the app up to a local drive and compact in an hour or so, then copy the compacted version back down.

      Thanks for your help. And sorry for the long muse. But if this rings any bells for anyone, or if anyone has suggestions, they would be welcome. Thanks again,

      -Bill

      Comment


      • #4
        RE: Data missing/corrupt

        I am a firm believer in never compacting databases, so I doubt that the problem lies in your failure to regularly compact. I don't understand why the same files work on your local machine that fail on the server. What happens to the autoincrement field? Does that magically correct itself also? It defies reason to think that the tables will be fixed simply by copying them to yor local drive and copying them back, *unless* it has something to do with fragmentation of the hard drive. Copying the files to another computer will defragment them.
        Rather than compacting the database, why don't you try to defragment the server? You can probably automate that to occur at 2 am on Sunday, when no one is likely to be affected.

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        • #5
          RE: Data missing/corrupt

          Could you expound on the reasons compaction is not recommended? I performed it for the first time after reading about it in a previous thread. I see no ill effects, yet.

          Tom Lyon

          Comment


          • #6
            RE: Data missing/corrupt

            Hello!

            Peter Wayne wrote:
            -------------------------------
            ... I doubt that the problem lies in your failure to regularly compact ... try to defragment
            -------------------------------

            I wrote a (long-winded) post about a week ago regarding a similar problem that I experienced in A5v3 and asked if the problem was fixed in v4 (apparently not).

            When playing with the v3 Invoice sample database by opening the Invoice set (invoice_header and invoice_items) and creating a one-to-many form with an embedded browse, I found that, on occasion, after deleting the last Invoice record (in invoice # order), all of the preceding invoice records would disappear!

            I only had about a half dozen or so records entered. And the disappearing act would only occur after some other record adds, changes, and deletes were performed.

            Reindexing the set did no good, as the records appeared not to exist. Viewing the set in default browse view (instead of my custom form) showed no records. However, opening and viewing the header and items tables separately display all the undeleted records. The only fix that I found was to pack to invoice table set. Then the records reappeared! I then reindexed for good measure.

            As a side note, I run a defragmenter on a regular basis (at least once a week if not more often, so my hard drive rarely has a serious degree of fragmentation.

            So the problem (at least on my system) seemed to involve the linked set and not the individual tables.

            I didn't receive any replies to my earlier posting so I thought I was the only one to experience such a problem, but now I know that I'm not alone.

            I look forward to hearing some good solutions!

            TIA,
            O.J.

            Comment


            • #7
              RE: Data missing/corrupt

              In answer to your question, the auto increment fails (or rather starts over at 1) due to the fact that a stretch of records in the table (several hundred to several thousand) appear to be completely blank, including the ID field (which is auto incremented. These records appear at the end of the table (in record number order), causing the ID to re-start at 1.

              If you PageUp and PageDown through the default browse in this table, records with this condition will display their data (in one page up or down) and it will not display the next time.

              I do not have control over our server hardware, but I believe that we recently begain using "Raid 5" technology to spread data over several drives. I am definately not familiar with server technology in general or that technology in particular, but maybe it's a factor.

              When the table is copied to a local drive, all of the records that appeard to have blank fields display their data correctly. This happens occasionally - maybe 4 time in the past 3 months - and has only happened recently. Any thoughts are appreciated.

              -Bill

              Comment


              • #8
                RE: Data missing/corrupt

                William:

                I would definitely check out your RAID 5 configuration. Do you know how many logical drives that you have on the server? There are a few ways to configure a RAID 5 system
                and it appears that your data is being separated to physical drives that Alpha 5 cannot find. When you copy it back to your C drive—Alpha can find what it needs. Then when you copy it to the server, it can find it—until the data begins to be placed in different
                hard drives. Your Raid Controller should automatically set this—but you can configure it, and if one of the physical drives has a problem, or is slower, than the other
                you Alpha might not get an appropriate response. Also, NT is fussy and needs to be Properly configured for a Raid Controller. Sometimes if you assign drive paths to tables
                or files, this can mess up a database like Alpha 5 in a Raid system.

                Good luck

                Comment


                • #9
                  RE: Data missing/corrupt

                  Elliot:

                  Thanks for your reply. I am out of my depth here, but I will bring your points up with our network/server people. Thanks again,

                  -Bill

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