stasis-aries-wal/lladd/bufferManager.h

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/**
 * @file
 * Manages the page buffer

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

 
  @todo Allow error checking!  
 
  @todo Make linux provide a better version of malloc().  We need to
  directly DMA pages into and out of userland, or setup mmap() so
  that it takes a flag that makes it page mmapped() pages to swap
  instead of back to disk. (munmap() and msync() would still hit the
  on-disk copy)
 
  @todo Refactoring for lock manager
 
  Possible interface for lockManager:

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

         Transactions,
	 Operations,
	 Predicates.

       LLADD 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
 * $Id$
 */

#ifndef __BUFFERMANAGER_H__
#define __BUFFERMANAGER_H__

#include <lladd/page.h>
#include <lladd/constants.h>

/**
 * initialize buffer manager
 * @return 0 on success
 * @return error code on failure
 */
int bufInit();

/**
 * @param pageid ID of the page you want to load
 * @return fully formed Page type
 * @return page with -1 ID if page not found
 */
Page loadPage(int pageid);

/**
 * allocate a record
 * @param xid The active transaction.
 * @param size The size of the new record
 * @return allocated record
 */
recordid ralloc(int xid, long size);

/**
 * Find a page with some free space.
 *
 */
 

/* *
 * This function updates the LSN of a page.
 * 
 * This is needed by the
 * recovery process to make sure that each action is undone or redone
 * exactly once.
 *
 * @ param LSN The new LSN of the page.
 * @ param pageid ID of the page you want to write
 *
 * @ todo This needs to be handled by ralloc and writeRecord for
 * correctness.  Right now, there is no way to atomically update a
 * page(!)  To fix this, we need to change bufferManager's
 * implementation to use read/write (to prevent the OS from stealing
 * pages in the middle of updates), and alter kickPage to see what the
 * last LSN synced to disk was.  If the log is too far behind, it will
 * need to either choose a different page, or call flushLog().  We may
 * need to implement a special version of fwrite() to do this
 * atomically.  (write does not have to write all of the data that was
 * passed to it...)
 */
/*void writeLSN(long LSN, int pageid);  */

/**
 * @param pageid ID of page you want to read
 * @return LSN found on disk
 */
long readLSN(int pageid);

/**
 * @param xid transaction id
 * @param rid recordid where you want to write
 * @param dat data you wish to write
 */
void writeRecord(int xid, lsn_t lsn, recordid rid, const void *dat);

/**
 * @param xid transaction ID
 * @param rid
 * @param dat buffer for data
 */
void readRecord(int xid, recordid rid, void *dat);

/**
 * Write page to disk, including correct LSN.  Doing so may require a
 * call to logSync().  There is not much that can be done to avoid
 * this call right now.  In the future, it might make sense to check
 * to see if some other page can be kicked, in order to avoid the log
 * flush.  
 *
 * @param page  The page to be flushed to disk.
 */
void pageWrite(const Page * dat);


/**
   Read a page from disk.  

   @param A page struct, with id set correctly.  The rest of this
   struct is filled out by pageMap.
*/
void pageRead(Page * ret);


/* int flushPage(Page page); */

/*void pageMap(Page * page); */
/*
 * this function does NOT write to disk, just drops the page from the active
 * pages
 * @param page to take out of buffer manager
 * @return 0 on success
 * @return error code on failure
int dropPage(Page page);
 */

/**
 * all actions necessary when committing a transaction. Can assume that the log
 * has been written as well as any other actions that do not depend on the
 * buffer manager
 *
 * Basicly, this call is here because we used to do copy on write, and
 * it might be useful when locking is implemented.
 *
 * @param xid transaction ID
 * @return 0 on success
 * @return error code on failure
 */
int bufTransCommit(int xid, lsn_t lsn);

/**
 * 
 * Currently identical to bufTransCommit.
 * 
 * @param xid transaction ID
 * @return 0 on success
 * @return error code on failure
 */
int bufTransAbort(int xid, lsn_t lsn);

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

/** @todo Global file descriptors are nasty. */

extern int blobfd0;
extern int blobfd1;


#endif