Museum

Home

Lab Overview

Retrotechnology Articles

⇒ Online Manual

Media Vault

Software Library

Restoration Projects

Artifacts Sought

Related Articles

Examples

/BUCKET

/RECORD

Bucket vbn

/INDEXNO

Record offset

ANALYZE/RMS_FILE POSITION — VMS 5.0

   This command provides a quick way to position to a structure in an
   in indexed file without performing the normal progression of "DOWN"
   and "NEXT" commands that would otherwise be required to get there.
   This command is also useful for positioning to a structure which
   would otherwise be inaccessible due to structural errors in the file.
   This command is much like a "GOTO" in a programming language in that
   it short-circuits the normal structured steps required to get to the
   structure.  One of the qualifiers /BUCKET or /RECORD must be included
   with this command.

Additional information available:

Examples

/BUCKET/RECORD

/BUCKET

   Positions you to a bucket of the file.  Once you have positioned to
   a bucket in this manner, you can continue to peruse the file forwards
   and downwards from this point just as if you had traversed the tree
   structure through the index structure down to this bucket.  However,
   if you go "UP" from this point, rather than traverse upward through
   the index structure, you will go immediately to the key descriptor
   for the bucket.

   This command blindly assumes that the bucket to which you position is
   a valid bucket and uses information in the bucket header to determine
   the context of the bucket, including the proper key descriptor and
   the legal down paths.  If you position to a reclaimed bucket or to a
   vbn which is not the beginning of a bucket, ANALYZE/RMS_FILE takes the
   information stored in what should be the bucket header at the beginning
   of the block, and infers the context for the bucket.  In most cases,
   the information at the beginning of an illegal bucket boundary does not
   make sense interpreted as a bucket header and causes many errors to be
   reported.

   If you use this command to position to a bucket and find that many
   error messages appear on your screen, you have probably not positioned
   to a vbn which is at the beginning of a bucket or have specified the
   wrong index number for the bucket. (See information below on the
   /INDEXNO qualifier.)

     Format:

        POSITION/BUCKET [/INDEXNO=n] Bucket_vbn

Additional information available:

Bucket vbn

/INDEXNO

Bucket vbn

   This parameter is the vbn of the bucket to which you wish you position.
   If a bucket is more than one block long, enter the vbn at which the
   bucket begins.  The notation for this argument is described in HELP
   RADIX.

/INDEXNO

   This qualifier allows the user to specify the number of the index in
   which the bucket falls.  For instance, "/INDEXNO=0" specifies that
   the bucket is a primary index bucket or a primary data bucket, and
   "/INDEXNO=1" specifies that the bucket resides in the 1st alternate
   index structure.

   This command is only necessary in those circumstances in which
   ANALYZE/RMS_FILE cannot infer the information on its own;
   specifically, (1) when the file is Prolog 1 or 2, or (2) when the
   user wants to override the index number found in the bucket header
   in a Prolog 3 file, perhaps because the bucket header has been
   corrupted.

   If you specify the wrong index number for a bucket, ANALYZE/RMS_FILE
   blindly assumes that the bucket belongs in the index which you
   specified and reports errors accordingly.

/RECORD

   Positions you at a record within the current bucket whether or not a
   valid record is found at this location and whether or not the bucket
   header is valid.  This command is only legal when you are positioned
   at a bucket header.

     Format:

        POSITION/RECORD Record_offset

Additional information available:

Record offset

Record offset

   This parameter specifies the offset in bytes from the beginning of
   the current bucket to the record to which you wish to position.
   The notation for this parameter is described in HELP RADIX.

Examples

    POSITION/BUCKET 23

        This command positions you to the bucket which begins at
        vbn 23 of the file.

    POSITION/BUCKET/INDEXNO=1 %X'2F'

        This command positions you to the bucket which begins at vbn 47
        of the file and presumes that the bucket resides in the first
        alternate index structure.

    POSITION/RECORD %X'0E'

        This command positions you to the record that begins 14 bytes
        from the beginning of the current bucket.  Note that this command
        is only legal while positioned to the bucket header.

Typewritten Software • bear@typewritten.org • Edmonds, WA 98026