stasis-aries-wal/stasis/bufferManager.h

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/**
 * @file
 * Manages the page buffer

    bufferManager - Provides cached page handling, delegates to blob
    manager when necessary.  Doesn't implement an eviction policy.
    That is left to a cacheManager.  (Multiple cacheManagers could be
    used with a single bufferManager.)

  @todo Allow error checking!

  @todo Refactoring for lock manager

  Possible interface for lockManager:

       Define three classes of objects that the lock manager is interested in:

         Transactions,
	 Operations,
	 Predicates.

       Stasis already has operations and transactions, and these can be
       relatively unchanged.  Predicates are read only operations that
       return a set of tuples.  Tread() is the simplest predicate.
       Index scans provide a motivating example.

       See http://research.microsoft.com/%7Eadya/pubs/icde00.pdf
       (Generalized Isolation Level Definitions, Adya, Liskov, O'Neil,
       2000) for a theoretical discussion of general locking schemes..

       Locking functions can return errors such as DEADLOCK, etc.
       When such a value is returned, the transaction aborts, and an
       error is passed up to the application.

       @ingroup BUFFER_MANAGER
 * $Id$
 */
#ifndef __BUFFERMANAGER_H__
#define __BUFFERMANAGER_H__
#include <stasis/common.h>
BEGIN_C_DECLS
/**
 * Obtain a pointer to a page from the buffer manager.  The page will
 * be pinned, and the pointer valid until releasePage is called.
 *
 * @param xid The transaction that is pinning the page (used by page-level locking implementations.)
 *
 * @param pageid ID of the page you want to load
 *
 * @return fully formed Page type
 */
Page * loadPage(int xid, pageid_t pageid);

Page * loadPageOfType(int xid, pageid_t pageid, pagetype_t type);

Page * loadUninitializedPage(int xid, pageid_t pageid);

Page * loadPageForOperation(int xid, pageid_t pageid, int op, int is_recovery);

void   prefetchPages(pageid_t pageid, pageid_t count);

/**
    Get a page from cache.  This function should never block on I/O.

    @return a pointer to the page, or NULL if the page is not in cache, or is being read from disk.
 */
Page * getCachedPage(int xid, const pageid_t pageid);

/**
   loadPage acquires a lock when it is called, effectively pinning it
   in memory.  releasePage releases this lock.
*/
void releasePage(Page *p);

typedef struct stasis_buffer_manager_t stasis_buffer_manager_t;

struct stasis_buffer_manager_t {
  Page * (*loadPageImpl)(stasis_buffer_manager_t*, int xid, pageid_t pageid, pagetype_t type);
  Page * (*loadUninitPageImpl)(stasis_buffer_manager_t*, int xid, pageid_t pageid);
  void   (*prefetchPages)(stasis_buffer_manager_t*, pageid_t pageid, pageid_t count);
  Page * (*getCachedPageImpl)(stasis_buffer_manager_t*, int xid, const pageid_t pageid);
  void   (*releasePageImpl)(stasis_buffer_manager_t*, Page * p);
  /**
      This is used by truncation to move dirty pages from Stasis cache
      into the operating system cache.  Once writeBackPage(p) returns,
      calling forcePages() will synchronously force page number p to
      disk.

      (Not all buffer managers support synchronous writes to stable
       storage.  For compatibility, such buffer managers should ignore
       this call.)

       @return 0 on success, ENOENT if the page is not in cache, and EBUSY if the page is pinned.
  */
  int    (*writeBackPage)(stasis_buffer_manager_t*, pageid_t p);
  /**
      Force any written back pages to disk.

      @see writeBackPage for more information.

      If the buffer manager doesn't support stable storage, this call is
      a no-op.
  */
  void   (*forcePages)(struct stasis_buffer_manager_t*);
  /**
      Force written back pages that fall within a particular range to disk.

      This does not force page that have not been written to with pageWrite().

      @param start the first pageid to be forced to disk
      @param stop the page after the last page to be forced to disk.
  */
  void   (*forcePageRange)(struct stasis_buffer_manager_t*, pageid_t start, pageid_t stop);
  void   (*stasis_buffer_manager_simulate_crash)(struct stasis_buffer_manager_t*);
  /**
   * Write out any dirty pages.  Assumes that there are no running transactions
   */
  void   (*stasis_buffer_manager_close)(struct stasis_buffer_manager_t*);
  void * impl;
};

#ifdef PROFILE_LATCHES_WRITE_ONLY
#define loadPage(x,y) __profile_loadPage((x), (y), __FILE__, __LINE__)
#define releasePage(x) __profile_releasePage((x))
compensated_function void  __profile_releasePage(Page * p);
compensated_function Page * __profile_loadPage(int xid, pageid_t pageid, char * file, int line);
#endif

END_C_DECLS

#endif