#include <db.h>

int
DB_MPOOLFILE->get(DB_MPOOLFILE *mpf,
    db_pgno_t *pgnoaddr, DB_TXN * txnid, u_int32_t flags, void **pagep);

The DB_MPOOLFILE->get method returns pages from the cache.

All pages returned by DB_MPOOLFILE->get will be retained (that is, pinned), in the pool until a subsequent call to DB_MPOOLFILE->put.

The returned page is size_t type aligned.

Fully or partially created pages have all their bytes set to a nul byte, unless the DB_MPOOLFILE->set_clear_len method was called to specify other behavior before the file was opened.

The DB_MPOOLFILE->get method will return DB_PAGE_NOTFOUND if the requested page does not exist and DB_MPOOL_CREATE was not set. Unless otherwise specified, the DB_MPOOLFILE->get method returns a non-zero error value on failure and 0 on success.

• The flags parameter 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 method, if specified, is called.
  DB_MPOOL_DIRTY
  • The page will be modified and must be written to the source file before being evicted from the pool. For files open with the DB_MULTIVERSION flag set, a new copy of the page will be made if this is the first time the specified transaction is modifying it.
  DB_MPOOL_EDIT
  • The page will be modified and must be written to the source file before being evicted from the pool. No copy of the page will be made, regardless of the DB_MULTIVERSION setting. This flag is only intended for use in situations where a transaction handle is not available, such as during aborts or recovery.
  DB_MPOOL_LAST
  • Return the last page of the source file, and copy its page number into the memory location to which pgnoaddr refers.
  DB_MPOOL_NEW
  • Create a new page in the file, and copy its page number into the memory location to which pgnoaddr refers. In this case, the pgin method, if specified, is not called.
  
  

  The DB_MPOOL_CREATE, DB_MPOOL_LAST, and DB_MPOOL_NEW flags are mutually exclusive.

• The pagep parameter references memory into which a pointer to the returned page is copied.

• If the flags parameter is set to DB_MPOOL_LAST or DB_MPOOL_NEW, the page number of the created page is copied into the memory location to which the pgnoaddr parameter refers. Otherwise, the pgnoaddr parameter is the page to create or retrieve.

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

• If the operation is part of an application-specified transaction, the txnid parameter is a transaction handle returned from DB_ENV->txn_begin; otherwise NULL. A transaction is required if the file is open for multiversion concurrency control by passing DB_MULTIVERSION to DB_MPOOLFILE->open and the DB_MPOOL_DIRTY, DB_MPOOL_CREATE or DB_MPOOL_NEW flags were specified. Otherwise it is ignored.

The DB_MPOOLFILE->get method may fail and return one of the following non-zero errors:

• The DB_MPOOL_DIRTY or DB_MPOOL_EDIT flag was set and the source file was not opened for writing.

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

• If 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.; or if an invalid flag value or parameter was specified.

• For transactions configured with DB_TXN_SNAPSHOT, the page has been modified since the transaction began.

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