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 LLADD_CORE
 * $Id$
 */

#include <stasis/constants.h>
#include <stasis/transactional.h>

#ifndef __BUFFERMANAGER_H__
#define __BUFFERMANAGER_H__

BEGIN_C_DECLS

/**
   Page is defined in bufferManager.h as an incomplete type to enforce
   an abstraction barrier between page.h and the rest of the system.

   If you need to muck with page internals, first consider the
   implications that doing so has on latching.  In particular, rwlatch
   is currently entirely handled in page.c.
*/
typedef struct Page_s Page_s;
typedef struct Page_s Page;

/**
 * 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, int pageid);

/** 
    This is the function pointer that bufInit sets in order to
    override loadPage.
*/
extern Page * (*loadPageImpl)(int xid, int pageid);
/**
   loadPage aquires a lock when it is called, effectively pinning it
   in memory.  releasePage releases this lock.
*/
void releasePage(Page *p);

/** 
    This is the function pointer that bufInit sets in order to
    override releasePage.
*/
extern void   (*releasePageImpl)(Page * p);
/**
 * initialize buffer manager
 * @return 0 on success
 * @return error code on failure
 */
/** 
    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.)
*/
extern void (*writeBackPage)(Page * 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.
*/
extern void (*forcePages)();

extern void (*simulateBufferManagerCrash)();

int bufInit(int type);
/**
 * will write out any dirty pages, assumes that there are no running
 * transactions
 */
extern void   (*bufDeinit)();

#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, int pageid, char * file, int line);
#endif


/*compensated_function Page * bufManLoadPage(int xid, int pageid);

void bufManReleasePage(Page * p);

int bufManBufInit();

void bufManBufDeinit();

void setBufferManager(int i); */


END_C_DECLS

#endif