stasis-aries-wal/src/lladd/page.h

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/**
 * @file
 *
 * interface for dealing with generic, lsn based pages
 *
 * This file provides a re-entrant interface for pages that are labeled
 * with an LSN and a page type.
 *
 * @ingroup LLADD_CORE
 * $Id$
 * 

 STRUCTURE OF A GENERIC PAGE
<pre>
 +----------------------------------------------------------------------+
 |                                                                      |
 |  USABLE SPACE                                                        |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                                      |
 |                                                    +-----------+-----+
 |                                                    | page type | LSN |
 +----------------------------------------------------+-----------+-----+
</pre>
  */

#ifndef __PAGE_H__
#define __PAGE_H__

#include <config.h>
#include <lladd/common.h>
#include "latches.h"
/** @todo page.h includes things that it shouldn't, and page.h should eventually be an installed header. */

#include <lladd/transactional.h>
#include <lladd/bufferManager.h>

BEGIN_C_DECLS

#define lsn_ptr(page)                   (((lsn_t*)(&((page)->memAddr[PAGE_SIZE])))-1)
#define page_type_ptr(page)             (((int*)lsn_ptr((page)))-1)
#define end_of_usable_space_ptr(page)   page_type_ptr((page))

#define shorts_from_end(page, count)  (((short*)end_of_usable_space_ptr((page)))-(count))
#define bytes_from_start(page, count) (((byte*)((page)->memAddr))+(count))
#define ints_from_start(page, count)  (((int*)((page)->memAddr))+(count))
#define ints_from_end(page, count)    (((int*)end_of_usable_space_ptr((page)))-(count))

#define USABLE_SIZE_OF_PAGE (PAGE_SIZE - sizeof(lsn_t) - sizeof(int))

/** 
    The page type contains in-memory information about pages.  This
    information is used by LLADD to track the page while it is in
    memory, and is never written to disk.

    In particular, our current page replacement policy requires two doubly
    linked lists, 

    @todo The Page struct should be tuned for better memory utilization.
*/
struct Page_s {
  /** @todo Shouldn't Page.id be a long? */
  int id;
  lsn_t LSN;
  byte *memAddr;
  byte dirty;
  /** The next item in the replacement policy's queue */
  struct Page_s *next;
  /** The previous item in the replacement policy's queue. */
  struct Page_s *prev; 
  /** Which queue is the page in? */
  int queue; 
  /** Is the page in the cache at all? */
  int inCache;

  /** Used for page-level latching.
      
      Each page has an associated read/write lock.  This lock only
      protects the internal layout of the page, and the members of the
      page struct.  Here is how rwlatch is held in various circumstances:
      
      Record allocation:  Write lock
      Record read:        Read lock
      Read LSN            Read lock
      Record write       *READ LOCK*
      Write LSN           Write lock
      Write page to disk  No lock
      Read page from disk No lock

      Any circumstance where one these locks are held during an I/O
      operation is a bug.  
      
      For the 'no lock' cases, @see loadlatch

  */
  
  rwl * rwlatch;

  /**
      Since the bufferManager re-uses page structs, this lock is used
      to ensure that the page is in one of two consistent states,
      depending on whether a read lock or a write lock is being held.
      If a read lock is held, then the page is managed by the rwlatch
      also defined in this struct.  Therefore, it cannot be read from
      or written to disk.  Furthermore, since we do not impose an
      order on operations, the holder of a readlock may not use the
      lsn field to determine whether a particular operation has
      completed on the page.

      The write lock is used to block all writers (other than the one
      holding the page), and to ensure that all updates with lsn less
      than or equal to the page's lsn have been applied.  Therefore,
      threads that write the page to disk must hold this lock.  Since
      it precludes access by all other threads, a write lock also
      allows the holder to evict the current page, and replace it.

      Examples:
      
      Write page to disk    Write lock
      Read page from disk   Write lock
      Allocate a new record Read lock
      Write to a record     Read lock
      Read from a record    Read lock


      @see rwlatch, getPage(), pageRalloc(), pageRead()
      
  */
  rwl * loadlatch;

};

/**
 * initializes all the global variables needed by the functions
 * dealing with pages.
 */
void pageInit();
/**
 * releases all resources held by the page sub-system.
 */
void pageDeInit();

/**
 * assumes that the page is already loaded in memory.  It takes as a
 * parameter a Page.  The Page struct contains the new LSN and the
 * page number to which the new LSN must be written to.  Furthermore,
 * this function updates the dirtyPages table, if necessary.  The
 * dirtyPages table is needed for log truncation.  (If the page->id is
 * null, this function assumes the page is not in the buffer pool, and
 * does not update dirtyPages.  Similarly, if the page is already
 * dirty, there is no need to udpate dirtyPages.
 *
 * @param page You must have a writelock on page before calling this
 * function.
 *
 * @param lsn The new lsn of the page.  If the new lsn is less than
 * the page's current lsn, then the page's lsn will not be changed.
 * If the page is clean, the new lsn must be greater than the old lsn.
 */
void pageWriteLSN(int xid, Page * page, lsn_t lsn);

/**
 * assumes that the page is already loaded in memory.  It takes
 * as a parameter a Page and returns the LSN that is currently written on that
 * page in memory.
 */
lsn_t pageReadLSN(const Page * page);

/**
 * @param xid transaction id @param lsn the lsn that the updated
 * record will reflect.  This is needed by recovery, and undo.  (The
 * lsn of a page must always increase.  Undos are handled by passing
 * in the LSN of the CLR that records the undo.)
 *
 * @param page a pointer to an in-memory copy of the page as it
 * currently exists.  This copy will be updated by writeRecord.
 *
 * @param rid recordid where you want to write 
 *
 * @param dat the new value of the record.
 *
 * @return 0 on success, lladd error code on failure
 *
 */
void writeRecord(int xid, Page * page, lsn_t lsn, recordid rid, const void *dat); 
/**
 *  The same as writeRecord, but does not obtain a latch on the page.
 */
void writeRecordUnlocked(int xid, Page * page, lsn_t lsn, recordid rid, const void *dat); 
/**
 * @param xid transaction ID
 * @param rid the record to be written
 * @param dat buffer for data
 * @return 0 on success, lladd error code on failure
 */
int readRecord(int xid, Page * page, recordid rid, void *dat);
/**
 *  The same as readRecord, but does not obtain a latch.
 */
int readRecordUnlocked(int xid, Page * p, recordid rid, void *buf);
/**
   Should be called when transaction xid commits.
*/
void pageCommit(int xid);
/**
   Should be called when transaction xid aborts.
*/
void pageAbort(int xid);

/** 
    Allocate memory to hold a new page.

    @return A pointer to the new page.  This memory is part of a pool,
    and should never be freed manually.  Instead, it should be passed
    into pageFree() so that it can be reused.
*/

int getRecordType(int xid, Page * p, recordid rid);

int getRecordSize(int xid, Page * p, recordid rid);
/**
   same as getRecordType(), but does not obtain a lock.
*/
int getRecordTypeUnlocked(int xid, Page * p, recordid rid);
/**
   return the length of the record rid.  (the rid parameter's size field will be ignored)

   @todo implement getRecordLength for blobs and fixed length pages.

   @return -1 if the field does not exist, the size of the field otherwise.
 */
int getRecordLength(int xid, Page * p, recordid rid);

END_C_DECLS

#endif