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< p > Library Version 11.2.5.2< / p >
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< th colspan = "3" align = "center" > DB_ENV-> set_app_dispatch()< / th >
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< td width = "20%" align = "left" > < a accesskey = "p" href = "envset_alloc.html" > Prev< / a > < / td >
< th width = "60%" align = "center" > Chapter
The DB_ENV Handle
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< h2 class = "title" style = "clear: both" > < a id = "envset_app_dispatch" > < / a > DB_ENV-> set_app_dispatch()< / h2 >
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< pre class = "programlisting" > #include < db.h>
int
DB_ENV-> set_app_dispatch(DB_ENV *dbenv,
int (*tx_recover)(DB_ENV *dbenv,
DBT *log_rec, DB_LSN *lsn, db_recops op)); < / pre >
< p >
Declare a function to be called during transaction abort and recovery
to process application-specific log records.
< / p >
< p >
The < code class = "methodname" > DB_ENV-> set_app_dispatch()< / code > method configures operations performed
using the specified < a class = "link" href = "env.html" title = "Chapter > DB_ENV< / a > handle, not all
operations performed on the underlying database environment.
< / p >
< p >
The < code class = "methodname" > DB_ENV-> set_app_dispatch()< / code > method may not be called after the
< a class = "xref" href = "envopen.html" title = "DB_ENV->open()" > DB_ENV-> open()< / a > method is
called. If the database environment already exists when
< a class = "xref" href = "envopen.html" title = "DB_ENV->open()" > DB_ENV-> open()< / a > is called, the
information specified to < code class = "methodname" > DB_ENV-> set_app_dispatch()< / code > must be
consistent with the existing environment or corruption can occur.
< / p >
< p >
The < code class = "methodname" > DB_ENV-> set_app_dispatch()< / code > method returns a non-zero error value
on failure and 0 on success.
< / p >
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< h3 class = "title" > < a id = "id3711267" > < / a > Parameters< / h3 >
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< h4 class = "title" > < a id = "id3711270" > < / a > tx_recover< / h4 >
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< p >
The < span class = "bold" > < strong > tx_recover< / strong > < / span > parameter is the
application's abort and recovery function. The function takes four
parameters:
< / p >
< div class = "itemizedlist" >
< ul type = "disc" >
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< p >
< code class = "literal" > dbenv< / code >
< / p >
< p >
The < span class = "bold" > < strong > dbenv< / strong > < / span > parameter is the enclosing
database environment handle.
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< / li >
< li >
< p >
< code class = "literal" > log_rec< / code >
< / p >
< p >
The < span class = "bold" > < strong > log_rec< / strong > < / span > parameter is a log
record.
< / p >
< / li >
< li >
< p >
< code class = "literal" > lsn< / code >
< / p >
< p >
The < span class = "bold" > < strong > lsn< / strong > < / span > parameter is a log sequence
number.
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< / li >
< li >
< p >
< code class = "literal" > op< / code >
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< p >
The < span class = "bold" > < strong > op< / strong > < / span > parameter is one of the
following values:
< / p >
< div class = "itemizedlist" >
< ul type = "circle" >
< li >
< p > < a id = "set_app_dispatch_DB_TXN_BACKWARD_ROLL" > < / a >
< code class = "literal" > DB_TXN_BACKWARD_ROLL< / code >
< / p >
< p >
The log is being read backward to determine which transactions have
been committed and to abort those operations that were not; undo the
operation described by the log record.
< / p >
< / li >
< li >
< p > < a id = "set_app_dispatch_DB_TXN_FORWARD_ROLL" > < / a >
< code class = "literal" > DB_TXN_FORWARD_ROLL< / code >
< / p >
< p >
The log is being played forward; redo the operation described by the
log record.
< / p >
< / li >
< li >
< p > < a id = "set_app_dispatch_DB_TXN_ABORT" > < / a >
< code class = "literal" > DB_TXN_ABORT< / code >
< / p >
< p >
The log is being read backward during a transaction abort; undo the
operation described by the log record.
< / p >
< / li >
< li >
< p > < a id = "set_app_dispatch_DB_TXN_APPLY" > < / a >
< code class = "literal" > DB_TXN_APPLY< / code >
< / p >
< p >
The log is being applied on a replica site; redo the operation
described by the log record.
< / p >
< / li >
< li >
< p > < a id = "set_app_dispatch_DB_TXN_PRINT" > < / a >
< code class = "literal" > DB_TXN_PRINT< / code >
< / p >
< p >
The log is being printed for debugging purposes; print the contents of
this log record in the desired format.
< / p >
< / li >
< / ul >
< / div >
< p >
The DB_TXN_FORWARD_ROLL and DB_TXN_APPLY operations frequently imply
the same actions, redoing changes that appear in the log record,
although if a recovery function is to be used on a replication client
where reads may be taking place concurrently with the processing of
incoming messages, DB_TXN_APPLY operations should also perform
appropriate locking. The macro DB_REDO(op) checks that the operation
is one of DB_TXN_FORWARD_ROLL or DB_TXN_APPLY, and should be used in
the recovery code to refer to the conditions under which operations
should be redone. Similarly, the macro DB_UNDO(op) checks if the
operation is one of DB_TXN_BACKWARD_ROLL or DB_TXN_ABORT.
< / p >
< / li >
< / ul >
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< p >
The function must return 0 on success and either < span class = "bold" > < strong > errno< / strong > < / span >
or a value outside of the Berkeley DB error name space on failure.
< / p >
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< h3 class = "title" > < a id = "id3711678" > < / a > Errors< / h3 >
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< / div >
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< p >
The < code class = "methodname" > DB_ENV-> set_app_dispatch()< / code > < span >
< span >
method may fail and return one of the following non-zero errors:
< / span >
< / span >
< / p >
< div class = "sect3" lang = "en" xml:lang = "en" >
< div class = "titlepage" >
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< h4 class = "title" > < a id = "id3711735" > < / a > EINVAL< / h4 >
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If the method was called after < a class = "xref" href = "envopen.html" title = "DB_ENV->open()" > DB_ENV-> open()< / a >
was called; or if an invalid flag value or parameter was specified.
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< h3 class = "title" > < a id = "id3711512" > < / a > Class< / h3 >
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< p >
< a class = "link" href = "env.html" title = "Chapter > DB_ENV< / a > , < a class = "link" href = "txn.html" title = "Chapter > DB_TXN< / a >
< / p >
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< h3 class = "title" > < a id = "id3711532" > < / a > See Also< / h3 >
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< p >
< a class = "xref" href = "txn.html#txnlist" title = "Transaction Subsystem and Related Methods" > Transaction Subsystem and Related Methods< / a >
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