btr — B Tree index recovery
btr [-a] [-d] [-f] [-k] [-n cnt] [-r] [-v] [--] old_file new_file
btr will attempt to recover key (and
optionally data) information from the B Tree index file
identified by old_file. The
recovered contents are written to the B Tree index file
identified by
new_file. btr
recovery is controlled by a number of arguments:
Table 6.1. Command Arguments
|
[ -k | -d ] |
Specifies recovery mode; -k for keys, -d for keys and data. Default if omitted is -k. | |
|
[-n |
Sets maximum number of io errors to ignore before terminating the recovery. Default is 0. | |
|
[-v] |
Causes btr to display information on the recovery process. This flag may be repeated up to three times to increase the level of information. For a large B Tree index this could lead to a significant amount of output. | |
|
[-a] |
If specified, the B Tree index in
| |
|
[-f] |
If specified, the B Tree index represented by
| |
|
[-r] |
Requests btr to attempt full
recovery mode even if the version of the
| |
|
[--] |
Causes btr to stop processing
command arguments. Should be used if
|
btr will attempt to open the input btree
file using the btree library version of
btopn. If this fails, the
btr version of
btopn is used instead, which bypasses
the consistency checks.
An attempt to read the superroot is made. If successful, the root names and root blocks are recorded. Only the roots present in the superroot are retained. Root names in any child blocks are ignored; the index structure may be damaged and therefore no attempt to traverse it is made.
Each block, starting from 1, is read. If marked as ZROOT,
ZINUSE or ZDUP the keys and values are extracted directly from
the in-memory array. If -k specified, the key and value
are written to the new_btree
index file. If -d specified, and the value is a valid
disk record address, an attempt is made to read the data
record. Data record addresses are stored in a supporting
bt index file (.bt_da.db),
to enable detection of circular references. If the data
record is read OK, the key and data record is written to
the new_file btree file. If
the data record cannot be read, only the key is written.
In version 4 (and later) of the BTree index, each ZINUSE
block contains the root block it belongs to. This data
allows btr to partition keys by their
roots. Only those roots recovered from the superroot will
be named as in the old_file.
Keys from other roots will be copied to new roots, named after
their root block number (e.g. root_19834).
btr will display summary statistics about the recovery on stdout when complete.
btr can be used to recover (or indeed migrate) data from earlier (i.e. pre-version 4) versions of a Btree index file. Since the root block numbers are not held in the ZINUSE blocks, keys can not be partitioned by root. Therefore, this facility is only really applicable to single-rooted B Tree index files.
