Berkeley DB: memp_fget
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,b+tree,btr ee,hash,hashing,transaction,transactions,locking,logging,access method,access me thods,java,C,C++

# memp_fget

`

###

    #include <db.h>

    int
    memp_fget(DB_MPOOLFILE *mpf,
        db_pgno_t *pgnoaddr, u_int32_t flags, void **pagep);

# Description

The memp_fget function copies a pointer to the page with the page number specified by pgnoaddr, from the source file in the DB_MPOOLFILE, into the memory location referenced by pagep. If the page does not exist or cannot be retrieved, memp_fget will fail.

Page numbers begin at 0, i.e., the first page in the file is page number 0, not page number 1.

The returned page is size_t type aligned.

The flags argument is specified by logically OR'ing together one or more of the following values:

DB_MPOOL_CREATE
  If the specified page does not exist, create it. In this case, the pgin function, if specified, is called.

DB_MPOOL_LAST
  Return the last page of the source file and copy its page number to the location referenced by pgnoaddr.

DB_MPOOL_NEW
  Create a new page in the file and copy its page number to the location referenced by pgnoaddr. In this case, the pgin function, if specified, is not called.

The DB_MPOOL_CREATE, DB_MPOOL_LAST and DB_MPOOL_NEW flags are mutually exclusive.

Created pages have all their bytes set to 0, unless otherwise specified when the file was opened.

All pages returned by memp_fget will be retained (i.e. pinned in the pool until a subsequent call to memp_fput.

The memp_fget function returns the value of errno on failure, and 0 on success.

# Errors

If a fatal error occurs in Berkeley DB, the memp_fget function may fail and return DB_RUNRECOVERY, at which point all subsequent database calls will also return DB_RUNRECOVERY.

The memp_fget function may fail and return errno for any of the errors specified for the following Berkeley DB and C library functions: DBmemp->pgin(3), DBmemp->pgout(3), abort(3), close(3), dbenv->db_paniccall(3), fcntl(3), fflush(3), fprintf(3), free(3), fstat(3), fsync(3), getenv(3), getpid(3), getuid(3), isdigit(3), log_compare, log_flush, lseek(3), malloc(3), memcmp(3), memcpy(3), memset(3), mmap(3), open(3), pread(3), pstat_getdynamic(3), pwrite(3), read(3), sigfillset(3), sigprocmask(3), stat(3), strerror(3), strlen(3), sysconf(3), time(3), unlink(3), vfprintf(3), vsnprintf(3), and write(3).

In addition, the memp_fget function may fail and return errno for the following conditions:

EAGAIN
  The page reference count has overflowed. (This should never happen unless there's a bug in the application.)

EINVAL
  An invalid flag value or parameter was specified.

  The DB_MPOOL_NEW flag was set and the source file was not opened for writing.

  The requested page does not exist and DB_MPOOL_CREATE was not set.

  More than one of DB_MPOOL_CREATE, DB_MPOOL_LAST and DB_MPOOL_NEW was set.

ENOMEM
  The cache is full and no more pages will fit in the pool.

# See Also

memp_close, memp_fclose, memp_fget, memp_fopen, memp_fput, memp_fset, memp_fsync, memp_open, memp_register, memp_stat, memp_stat, memp_sync, memp_trickle and memp_unlink.`