+I'Berkeley DB: DbLog::open[P

DbLog::open





#include <db_cxx.h>

static intDbLog::open(const char *dir,> u_int32_t flags, int mode, DbEnv *dbenv, DbLog **regionp);





Description



The DbLog::openFmethod copies a pointer, to the log identified by the directoryBdir, into the memory location referenced by regionp.

The;dir pathname argument is interpreted as described in@Berkeley DB File Naming.

EIf the log region is being created and log files are already present,@the log files are recovered and subsequent log writes areappended to the end of the log.

BThe log is stored in one or more files in the specified directory.;Each file is named using the format log.NNNNN, where?NNNNN is the sequence number of the file within the log.For further information, see8Log File Limits.

KThe flags and mode arguments specify how files will be opened,and/or created if they do not already exist.SThe flags value is specified by logically OR'ing together one or more of thefollowing values:

[

DB_CREATE
Create any underlying files, as necessary. If the files do not alreadyBexist and the DB_CREATE flag is not specified, the call will fail.Y

DB_THREAD
Cause the m4_reg(DB_LOG) handle returned by DbLog::open to be useable>by multiple threads within a single address space, i.e., to befree-threaded.


VAll files created by the log subsystem are created with mode mode (as describedHin chmod(2)) and modified by the process' umask value at the time$of creation (see umask(2)))).IThe group ownership of created files is based on the system and directory6defaults, and is not further specified by Berkeley DB.

#The logging subsystem is configuredEbased on the dbenv argument. It is expected that applicationsiwill use a single DbEnv object as the argument to all of thessubsystems in the Berkeley DB package. The fields of the DbEnv object(used by DbLog::open are described below.pReferences to the DbEnv object are maintained by Berkeley DB, so itDis necessary that the object and memory it references be valid untilthe object is destroyed.mAny of the DbEnv fields that are not explicitly set will defaultto appropriate values.

oThe following fields in the DbEnv object may be initialized, using7the appropriate set method, before calling DbLog::open:

>

void *(*db_errcall)(char *db_errpfx, char *buffer);

FILE *db_errfile;

const char *db_errpfx;
'
class ostream *db_error_stream;
y
int db_verbose;
The error fields of the DbEnv behave as described for>DbEnv::appinit.S

u_int32_t lg_max;
The maximum size of a single file in the log, in bytes.cBecause DbLsn file offsets are unsigned 4-byte values,Glg_max may not be larger than the maximum unsigned 4-byte value.

8If lg_max is 0, a default value of 10Mb. is used.

;See Log File Limitsfor more information.



The DbLog::open>method either returns errno or throws an exception that:encapsulates an errno on failure, and 0 on success.

Environment Variables





DB_HOME
AIf the dbenv argument to DbLog::open was initialized usingiDbEnv::appinit the environment variable DB_HOME mayBbe used as the path of the database home for the interpretation of=the dir. Specifically, DbLog::open is affected by the)configuration string value of DB_LOG_DIR.


X

TMPDIR
If the dbenv argument to DbLog::open was NULL or not initializednusing DbEnv::appinit the environment variable TMPDIR mayDbe used as the directory in which to create the log, as described in DbLog::open.




Errors

RIf a fatal error occurs in Berkeley DB, the DbLog::open method may fail and eitherIreturn DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY,Gat which point all subsequent database calls will also fail in the sameFway. Methods marked as returning errno will, by default, throwHan exception that encapsulates the error information. The default error\behavior can be changed, see DbException.

The DbLog::open&method may fail and throw an exceptionKfor any of the errors specified for the following Berkeley DB and C library functions: abort(3),atoi(3), close(3), closedir(3),>DbEnv::version, fcntl(3), fflush(3), fprintf(3),free(3), fstat(3), fsync(3), getenv(3), getpid(3), getuid(3), isdigit(3),<DbLog::unlink, lseek(3), malloc(3), memcpy(3), memset(3),mmap(3), munmap(3),open(3), opendir(3),pstat_getdynamic(3),read(3), readdir(3), realloc(3), shmat(3), shmctl(3), shmdt(3),sigfillset(3),sigprocmask(3), snprintf(3),stat(3), strchr(3), strerror(3), strlen(3), strncmp(3), sysconf(3), unlink(3), vfprintf(3), vsnprintf(3),and write(3).In addition, the DbLog::open&method may fail and throw an exceptionor return errnofor the following conditions:

R

EAGAIN
The shared memory region was locked and (repeatedly) unavailable.
B

EINVAL
An invalid flag value or parameter was specified.

FThe DB_THREAD flag was specified and spinlocks are not implemented forthis architecture.

&The specified file size was too large.





Class

2DbLog



See Also

>DbLog::archive,:DbLog::close,>DbLog::compare,8DbLog::file,:DbLog::flush,6DbLog::get, DbLog::open,6DbLog::put,FDbLog::db_register,8DbLog::stat,;DbLog::unlinkandJDbLog::db_unregister.
ÿÿ