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

# memp_fget |

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    #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 value must be set to 0 or by bitwise inclusively 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 a non-zero error value on failure and 0 on success.

# Errors

The memp_fget function may fail and return a non-zero error 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.

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

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

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

The memp_fget function may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the memp_fget function may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# See Also

DBENV->set_mp_mmapsize, memp_fclose, memp_fget, memp_fopen, memp_fput, memp_fset, memp_fsync, memp_register, memp_stat, memp_sync and memp_trickle.`

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