gecko-dev/db/man/mancxx.roff/db_recover.1

.ds TYPE C
.\"
.\" See the file LICENSE for redistribution information.
.\"
.\" Copyright (c) 1996, 1997, 1998
.\"	Sleepycat Software.  All rights reserved.
.\"
.\"	@(#)db_recover.so	10.11 (Sleepycat) 4/10/98
.\"
.\"
.\" See the file LICENSE for redistribution information.
.\"
.\" Copyright (c) 1997, 1998
.\"	Sleepycat Software.  All rights reserved.
.\"
.\"	@(#)macros.so	10.45 (Sleepycat) 5/4/98
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.\" The general information text macro.
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.ie '\*[TYPE]'C'\{The DB library is a family of groups of functions that provides a modular
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are useful independent of the other DB classes,
although some classes are explicitly based on other classes
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For a general description of the DB package, see
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.\" The library error macro, the local error macro.
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for any of the errors specified for the following DB and library functions:
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[EAGAIN]
A lock was unavailable.
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[EBUSY]
The shared memory region was in use and the force flag was not set.
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[EAGAIN]
The shared memory region was locked and (repeatedly) unavailable.
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[EACCES]
An attempt was made to modify a read-only database.
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.na
.IR db_archive (1),
.IR db_checkpoint (1),
.IR db_deadlock (1),
.IR db_dump (1),
.IR db_load (1),
.IR db_recover (1),
.IR db_stat (1),
.IR db_intro (3),
.ie '\*[TYPE]'C'\{\
.IR db_appinit (3),
.IR db_cursor (3),
.IR db_dbm (3),
.IR db_internal (3),
.IR db_lock (3),
.IR db_log (3),
.IR db_mpool (3),
.IR db_open (3),
.IR db_thread (3),
.IR db_txn (3)
\}
.el\{\
.IR db_internal (3),
.IR db_thread (3),
.IR Db (3),
.IR Dbc (3),
.IR DbEnv (3),
.IR DbException (3),
.IR DbInfo (3),
.IR DbLock (3),
.IR DbLockTab (3),
.IR DbLog (3),
.IR DbLsn (3),
.IR DbMpool (3),
.if !'\*[TYPE]'JAVA'\{\
.IR DbMpoolFile (3),
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.IR Dbt (3),
.IR DbTxn (3),
.IR DbTxnMgr (3)
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.Hy
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.\" The function header macro.
.\" This macro takes one argument:
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.in 2
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.in
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.\" This macro takes two arguments:
.\"	+ the interface, e.g., "transaction region"
.\"	+ the prefix, e.g., "txn" (or the class name for C++, e.g., "DbTxn")
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.Fn \\$2_open
The
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.\"	+ the function called to open, e.g., "txn_open"
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The following fields in the DbEnv object may be initialized, using the
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.\" The DB_ENV common fields macros.
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.\" The open flags.
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The
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and
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The flags value is specified by
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.Sj DB_CREATE
Create any underlying files, as necessary.
If the files do not already exist and the DB_CREATE flag is not specified,
the call will fail.
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.\" DB_THREAD open flag macro.
.\" This macro takes two arguments:
.\"	+ the open function name
.\"	+ the object it returns.
.de Ft
.TP 5
.Sj DB_THREAD
Cause the \\$2 handle returned by the
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.\" The mode macro.
.\" This macro takes one argument:
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All files created by the \\$1 are created with mode
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(as described in
.IR chmod (2))
and modified by the process' umask value at the time of creation (see
.IR umask (2)).
The group ownership of created files is based on the system and directory
defaults, and is not further specified by DB.
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.\" The application exits macro.
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The
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utility exits 0 on success, and >0 if an error occurs.
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.\" The application -h section.
.\" This macro takes one argument:
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DB_HOME
If the
.B \-h
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.I DB_HOME
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.\" The function DB_HOME ENVIRONMENT VARIABLES section.
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is affected by the configuration string value of \\$2.\}
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.\" The function TMPDIR ENVIRONMENT VARIABLES section.
.\" This macro takes two arguments:
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.\"	+ the prefix, e.g., "txn" (or the class name for C++, e.g., "DbTxn")
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TMPDIR
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create the \\$1,
as described in the
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section above.
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.\" The unused flags macro.
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The
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parameter is currently unused, and must be set to 0.
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.\" The no-space TP macro.
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.TP 5
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.\" The return values of the functions macros.
.\" Rc is the standard two-value return with a suffix for more values.
.\" Ro is the standard two-value return but there were previous values.
.\" Rt is the standard two-value return, returning errno, 0, or < 0.
.\" These macros take one argument:
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The
.I \\$1
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on failure and 0 on success.
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on failure.
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..
.\" The TXN id macro.
.de Tx
.IP
If the file is being accessed under transaction protection,
the
.I txnid
parameter is a transaction ID returned from
.IR txn_begin ,
otherwise, NULL.
..
.\" The XXX_unlink function text macro.
.\" This macro takes two arguments:
.\"	+ the interface, e.g., "transaction region"
.\"	+ the prefix (for C++, this is the class name)
.de Un
.ie '\*[TYPE]'C'\{\
.ds Va db_appinit
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.Fn \\*(Vu
The
.I \\*(Vu
.Al function method
destroys the \\$1 identified by the directory
.IR dir ,
removing all files used to implement the \\$1.
.ie '\\$2'log' \{(The log files themselves and the directory
.I dir
are not removed.)\}
.el \{(The directory
.I dir
is not removed.)\}
If there are processes that have called
.I \\*(Vo
without calling
.I \\*(Vc
(i.e., there are processes currently using the \\$1),
.I \\*(Vu
will fail without further action,
unless the force flag is set,
in which case
.I \\*(Vu
will attempt to remove the \\$1 files regardless of any processes
still using the \\$1.
.PP
The result of attempting to forcibly destroy the region when a process
has the region open is unspecified.
Processes using a shared memory region maintain an open file descriptor
for it.
On UNIX systems, the region removal should succeed
and processes that have already joined the region should continue to
run in the region without change,
however processes attempting to join the \\$1 will either fail or
attempt to create a new region.
On other systems, e.g., WNT, where the
.IR unlink (2)
system call will fail if any process has an open file descriptor
for the file,
the region removal will fail.
.PP
In the case of catastrophic or system failure,
database recovery must be performed (see
.IR db_recover (1)
or the DB_RECOVER and DB_RECOVER_FATAL flags to
.IR \\*(Va (3)).
Alternatively, if recovery is not required because no database state is
maintained across failures,
it is possible to clean up a \\$1 by removing all of the
files in the directory specified to the
.I \\*(Vo
.Al function, method,
as \\$1 files are never created in any directory other than the one
specified to
.IR \\*(Vo .
Note, however,
that this has the potential to remove files created by the other DB
subsystems in this database environment.
.PP
.Rt \\*(Vu
.rm Va
.rm Vo
.rm Vu
.rm Vc
..
.\" Signal paragraph for standard utilities.
.\" This macro takes one argument:
.\"	+ the utility name.
.de Si
The
.I \\$1
utility attaches to DB shared memory regions.
In order to avoid region corruption,
it should always be given the chance to detach and exit gracefully.
To cause
.I \\$1
to clean up after itself and exit,
send it an interrupt signal (SIGINT).
..
.\" Logging paragraph for standard utilities.
.\" This macro takes one argument:
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.de Pi
.B \-L
Log the execution of the \\$1 utility to the specified file in the
following format, where ``###'' is the process ID, and the date is
the time the utility starting running.
.sp
\\$1: ### Wed Jun 15 01:23:45 EDT 1995
.sp
This file will be removed if the \\$1 utility exits gracefully.
..
.\" Malloc paragraph.
.\" This macro takes one argument:
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.if !'\*[TYPE]'JAVA'\{\
\\$1 are created in allocated memory.
If
.I db_malloc
is non-NULL,
it is called to allocate the memory,
otherwise,
the library function
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is used.
The function
.I db_malloc
must match the calling conventions of the
.IR malloc (3)
library routine.
Regardless,
the caller is responsible for deallocating the returned memory.
To deallocate the returned memory,
free each returned memory pointer;
pointers inside the memory do not need to be individually freed.
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..
.\" Underlying function paragraph.
.\" This macro takes two arguments:
.\"	+ the function name
.\"	+ the utility name
.de Uf
The
.I \\$1
.Al function method
is the underlying function used by the
.IR \\$2 (1)
utility.
See the source code for the
.I \\$2
utility for an example of using
.I \\$1
in a UNIX environment.
..
.\" Underlying function paragraph, for C++.
.\" This macro takes three arguments:
.\"	+ the C++ method name
.\"	+ the function name for C
.\"	+ the utility name
.de Ux
The
.I \\$1
method is based on the C
.I \\$2
function, which
is the underlying function used by the
.IR \\$3 (1)
utility.
See the source code for the
.I \\$3
utility for an example of using
.I \\$2
in a UNIX environment.
..
.TH DB_RECOVER 1 "April 10, 1998"
.UC 7
.SH NAME
db_recover \- the DB database recovery utility
.SH SYNOPSIS
\fBdb_recover\fP [\fB-cv\fP] [\fB-h home\fP]
.SH DESCRIPTION
The
.I db_recover
utility must be run after an unexpected application, DB, or system failure to
restore the database to a consistent state.
All committed transactions are guaranteed to appear after
.I db_recover
has run, and all uncommitted transactions will be completely undone.
.PP
The options are as follows:
.TP 5
.B \-c
Failure was catastrophic.
.TP 5
.B \-h
Specify a home directory for the database.
.TP 5
.B \-v
Run in verbose mode.
.PP
In the case of catastrophic failure, an archival copy,
or ``snapshot'' of all database files must be restored along with all of the
log files written since the database file snapshot was made.
(If disk space is a problem, log files may be referenced by symbolic links).
For further information on creating a database snapshot, see ``DB ARCHIVAL
PROCEDURES'' in
.IR db_archive (1).
.PP
If the failure was not catastrophic,
the files present on the system at the time of failure are sufficient
to perform recovery.
.PP
If log files are missing,
.I db_recover
will identify the missing log file(s) and fail,
in which case the missing log files need to be restored and recovery
performed again.
.PP
.Si db_recover
.PP
.Ex db_recover
.SH "FILESYSTEM OPERATIONS
.ft B
Filesystem operations,
e.g., moving the database environment to a different machine or file creation,
deletion or renaming, cannot be transaction protected.
.ft R
For this reason,
.I db_recover
cannot re-create, delete or rename files as part of recovery.
.PP
If
.I db_recover
cannot find a database file referenced in the log, it will output a warning
message that it was unable to locate a file it expected to find.
This message is only a warning, as the file may have subsequently been
deleted as part of normal database operations before the failure occurred.
.ft B
Note that committed transactions that involved these missing files are rolled
forward, even though the files were not found.
If the files were not intentionally deleted (e.g., they were created after
the last database snapshot, but were lost during a failure), they
must be manually created (using
.IR db_open (3)),
and
.I db_recover
must be rerun.
.ft R
.PP
Generally, it is simplest to perform filesystem operations at the same time as
making a snapshot of the database.
To perform filesystem operations:
.RS
.TP 5
1.
Cleanly shutdown database operations.
.Nt
2.
Rename, create or delete files.
.Nt
3.
Make a snapshot of the database.
.Nt
4.
Restart database applications.
.RE
.PP
To cleanly shutdown database operations,
all applications accessing the database environment must be shutdown.
If the applications are not implemented such that they can be shutdown
gracefully (i.e., closing all references to the database environment),
.I db_recover
must be run after all applications have been killed to ensure that the
underlying database is consistent and flushed to disk.
.SH "RECOVERY
After an application or system failure,
there are two possible approaches to database recovery.
If there is no need to retain state across the failure,
and all databases can be started anew,
the database home directory can simply be removed and recreated.
If it is necessary to retain persistent state across failures,
then the
.IR db_recover (1)
utility should be run for each DB application environment, i.e.,
each database home directory.
.PP
The
.I db_recover
utility will remove all the shared regions (which may have been corrupted
by the failure),
establish the end of the log by identifying the last record written to the
log,
and then perform transaction recovery.
Database applications must not be restarted until recovery completes.
During transaction recovery,
all changes made by aborted transactions are undone and all changes made by
committed transactions are redone, as necessary.
After recovery runs,
the environment is properly initialized so that applications may be restarted.
Any time an application crashes or the system fails,
.I db_recover
should be run on any exiting database environments.
.PP
Additionally,
there are two forms of recovery: normal recovery and catastrophic recovery.
The DB package defines catastrophic failure to be failure where either the
database or log files have been destroyed or corrupted from the point of
view of the filesystem.
For example,
catastrophic failure includes the case where the disk drive on which either
the database or logs are stored has crashed,
or when filesystem recovery is unable to bring the database and log files
to a consistent state with respect to the filesystem.
If the failure is non-catastrophic, i.e., the database files and log
are accessible on a filesystem that has recovered cleanly,
.I db_recover
will review the logs and database files to ensure that all committed
transactions appear and that all uncommitted transactions are undone.
If the failure is catastrophic,
a snapshot of the database files and the archived log files must be restored
onto the system.
Then
.I db_recover
will review the logs and database files to bring the database to a
consistent state as of the date of the last archived log file.
Only transactions committed before that date will appear in the database.
See
.I db_archive (1)
for specific information about archiving and recovering databases
after catastrophic failure.
.PP
.SH "ENVIRONMENT VARIABLES"
The following environment variables affect the execution of
.IR db_recover :
.TP 5
.Dh db_recover
.SH BUGS
Future versions of DB are expected to remove the restriction that database
files must be manually created before recovery is performed.
.SH "SEE ALSO"
.Gn
.PP
.Sa