Repairing Synchronized Databases


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Thread: Repairing Synchronized Databases

  1. #1
    Tara Guest

    Repairing Synchronized Databases


    Hi,
    When you are forced to repair a synchronized Access 97 database (due to the
    famous "Unrecognized Database Format" error), whether it is the Design Master
    or the Replica, the database is no longer replicable. I am getting this
    error two or three times a day and being forced to rollback and loose updates
    to records.

    First, what are the most common causes for this error and how do I decrease
    the occurance of it?

    Second, is there anything I can do to keep a database replicable after being
    forced to repair it?

    Please Help...loosing production time....

    Thank you.
    Tara

  2. #2
    Ted McNeal Guest

    Re: Repairing Synchronized Databases


    Tara,

    I’ll answer your questions then offer a general suggestion that is truly
    worth the effort.

    JET databases are inherently exposed to file system or network problems.
    The most problematic tables are those with memo or blob fields. Writing
    to these fields from a networked computer can span more than one packet.
    The issue with replicable tables is that they all have a system field ‘s_Lineage’
    which is a blob.

    I have seen issues such as bad cat-5 cables, malfunctioning OS on either
    the client or file server, and a bad hub cause the database to crash. Nearly
    all of the time the problem occurs in a memo or blob field. You can determine
    the culprit by reading the ldb file using the Microsoft utility ldbview.exe.
    When a database is flagged as suspect no engine will remove the associated
    ldb file. This allows you to perform such an inspection even though all
    users are logged out of the database. The workstation that caused the database
    to become corrupted will read yes under the column suspect where the workstation’s
    name is the user name.

    Sometimes, the database that you restore has issues, either structural or
    data related, and will eventually be flagged as suspect.

    The idea behind making a database not replicable upon repair is that the
    database may still have issues that could pollute the design master and other
    replicas. Hence, you cannot restore a database without it being flagged
    as not-replicable, as this is an intentional action on the part of the engine’s
    repair process.

    One thing you can do is to setup a replica farm at each instance of a replica
    and at the hub. A replica farm consists of two or more (usually two or three)
    replicas that co-exist on a specific computer and are set to synchronize
    with each other every 15 minutes. This schedule is set by using the Jet
    replication manager, which is a component of the Office 97 ODE tools. All
    users will be designated to use only one of the replicas. Whereas the others
    act as warm backups in the event that the user’s database is flagged as suspect.

    One thing you can do to hedge against data loss in the replica set, is to
    implement a field that records the date and time when the record was last
    updated and move the data to a warm backup. The problem with a Jet database
    is that it does not support triggers, hence the aforementioned implementation
    must occur in the application. Of course you have the option of implementing
    this on only critical-frequently updates tables.

    As for my suggestion, I would strongly advise you begin thinking about porting
    your database to SQL Server and implement merge replication. You can get
    white papers on setting up merge replication from Microsoft www.microsoft.com/sql
    or from Mr. Hotek’s website www.mssqlserver.com.

    I still use JET databases for moving data and for some specialized data transferring
    that require the mobility and security of a jet database. I also use Jet
    as part of my MS Access development in which I use ODBC Direct to communicate
    with SQL Server. Yet, I truly enjoy working with SQL Server and merge replication.
    The stability and functionality cannot begin to compare with Jet.

    Ted McNeal
    tmcneal@mhsinc.org





    "Tara" <tarac@execpc.com> wrote:
    >
    >Hi,
    >When you are forced to repair a synchronized Access 97 database (due to

    the
    >famous "Unrecognized Database Format" error), whether it is the Design Master
    >or the Replica, the database is no longer replicable. I am getting this
    >error two or three times a day and being forced to rollback and loose updates
    >to records.
    >
    >First, what are the most common causes for this error and how do I decrease
    >the occurance of it?
    >
    >Second, is there anything I can do to keep a database replicable after being
    >forced to repair it?
    >
    >Please Help...loosing production time....
    >
    >Thank you.
    >Tara



  3. #3
    Robert Guest

    Re: Repairing Synchronized Databases


    "Tara" <tarac@execpc.com> wrote:
    >
    >Hi,
    >When you are forced to repair a synchronized Access 97 database (due to

    the
    >famous "Unrecognized Database Format" error), whether it is the Design Master
    >or the Replica, the database is no longer replicable. I am getting this
    >error two or three times a day and being forced to rollback and loose updates
    >to records.
    >
    >First, what are the most common causes for this error and how do I decrease
    >the occurance of it?
    >
    >Second, is there anything I can do to keep a database replicable after being
    >forced to repair it?
    >
    >Please Help...loosing production time....
    >
    >Thank you.
    >Tara



    Tara,

    I have had this same problem, the only thing I could track down was network
    problems eventually I had to move my DB to SQL Server, this solved the problem
    as SQL Server is much more reliable. However short of that you might try
    the Jetcomp.exe utility (download from microsoft) Jetcomp.exe is able to
    repair .mdb files more successfuly than native compact/repair.

    Good luck

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