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

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/************************************************************************
 * implementation of pages

 STRUCTURE OF A PAGE

 +-------------------------------------------+-----------------------+--+
 | DATA SECTION                   +--------->| RID: (PAGE, 0)        |  |
 |          +-----------------+   |          +-----------------------+  |
 |      +-->| RID: (PAGE, 1)  |   |                                     |
 |      |   +-----------------+   |                                     |
 |      |                         |                                     |
 |      +-----------------+       |        +----------------------------+
 |                        |       |   +--->| RID: (PAGE, n)             |
 |                        |       |   |    +----------------------------+
 |======================================================================|
 |^ FREE SPACE            |       |   |                                 |
 |+-----------------------|-------|---|--------------------+            |
 |                        |       |   |                    |            |
 |          +-------------|-------|---+                    |            |
 |          |             |       |                        |            |
 |      +---|---+-----+---|---+---|---+--------------+-----|------+-----+
 |      | slotn | ... | slot1 | slot0 | num of slots | free space | LSN |
 +------+-------+-----+-------+-------+--------------+------------+-----+

 NOTE:
   - slots are zero indexed.
   - slots are of implemented as (offset, length)

 Latching summary:

   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 it 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
 
 Any circumstance where these locks are held during an I/O operation
 is a bug.
 
 $Id$

************************************************************************/

#include <config.h>
#include <lladd/common.h>
#include "page.h"

#include <assert.h>
#include <stdio.h>

/*#include "latches.h" */
#include <lladd/constants.h>

/* TODO:  Combine with buffer size... */
static int nextPage = 0;

static const byte *slotMemAddr(const byte *memAddr, int slotNum) ;

/** @todo:  Why does only one of the get/set First/Second HalfOfWord take an unsigned int? */
static int getFirstHalfOfWord(unsigned int *memAddr);
static int getSecondHalfOfWord(int *memAddr);
static void setFirstHalfOfWord(int *memAddr, int value);
static void setSecondHalfOfWord(int *memAddr, int value);

static int readFreeSpace(byte *memAddr);
static void writeFreeSpace(byte *memAddr, int newOffset);
static int readNumSlots(byte *memAddr);
static void writeNumSlots(byte *memAddr, int numSlots);

static int getSlotOffset(byte *memAddr, int slot) ;
static int getSlotLength(byte *memAddr, int slot) ;
static void setSlotOffset(byte *memAddr, int slot, int offset) ;
static void setSlotLength(byte *memAddr, int slot, int length) ;

/** @todo replace static ints in page.c with #defines. */

/* ------ */

static int SLOT_OFFSET_SIZE;
static int SLOT_LENGTH_SIZE;
static int SLOT_SIZE;

static int LSN_SIZE;
static int FREE_SPACE_SIZE;
static int NUMSLOTS_SIZE;

static int START_OF_LSN;
static int START_OF_FREE_SPACE;
static int START_OF_NUMSLOTS;

static int MASK_0000FFFF;
static int MASK_FFFF0000;

/* ------ */

static pthread_mutex_t pageAllocMutex;
Page pool[MAX_BUFFER_SIZE];


int isValidSlot(byte *memAddr, int slot);
void invalidateSlot(byte *memAddr, int slot);
void pageDeRalloc(Page * page, recordid rid);

/**
   The caller of this function must already have a writelock on the
   page.
*/
static void pageCompact(Page * page);

/**
 * pageInit() initializes all the important variables needed in
 * all the functions dealing with pages.
 */
void pageInit() {

  nextPage = 0;
	/**
	 * For now, we will assume that slots are 4 bytes long, and that the
	 * first two bytes are the offset, and the second two bytes are the
	 * the length.  There are some functions at the bottom of this file
	 * that may be useful later if we decide to dynamically choose
	 * sizes for offset and length.
	 */

	/**
	 * the largest a slot length can be is the size of the page,
	 * and the greatest offset at which a record could possibly 
	 * start is at the end of the page
	 */
	SLOT_LENGTH_SIZE = SLOT_OFFSET_SIZE = 2; /* in bytes */
	SLOT_SIZE = SLOT_OFFSET_SIZE + SLOT_LENGTH_SIZE;

	LSN_SIZE = sizeof(long);
	FREE_SPACE_SIZE = NUMSLOTS_SIZE = 2;

	/* START_OF_LSN is the offset in the page to the lsn */
	START_OF_LSN = PAGE_SIZE - LSN_SIZE;
	START_OF_FREE_SPACE = START_OF_LSN - FREE_SPACE_SIZE;
	START_OF_NUMSLOTS = START_OF_FREE_SPACE - NUMSLOTS_SIZE;

	MASK_0000FFFF = (1 << (2*BITS_PER_BYTE)) - 1;
	MASK_FFFF0000 = ~MASK_0000FFFF;

	
	pthread_mutex_init(&pageAllocMutex, NULL);
}

void pageCommit(int xid) {
  /*	 rmTouch(xid); */
}

void pageAbort(int xid) {
  /* rmTouch(xid); */
}


static int getFirstHalfOfWord(unsigned int *memAddr) {
  unsigned int word = *memAddr;
  word = (word >> (2*BITS_PER_BYTE)); /* & MASK_0000FFFF; */
  return word;
}


static int getSecondHalfOfWord(int *memAddr) {
	int word = *memAddr;
	word = word & MASK_0000FFFF;
	return word;
}


void setFirstHalfOfWord(int *memAddr, int value){
	int word = *memAddr;
	word = word & MASK_0000FFFF;
	word = word | (value << (2*BITS_PER_BYTE));
	*memAddr = word;
}


void setSecondHalfOfWord(int *memAddr, int value) {
	int word = *memAddr;;
	word = word & MASK_FFFF0000;
	word = word | (value & MASK_0000FFFF);
	*memAddr = word;
}

/**
 * slotMemAddr() calculates the memory address of the given slot.  It does this 
 * by going to the end of the page, then walking backwards, past the LSN field
 * (LSN_SIZE), past the 'free space' and 'num of slots' fields (NUMSLOTS_SIZE),
 * and then past a slotNum slots (slotNum * SLOT_SIZE).
 */
static const byte *slotMemAddr(const byte *memAddr, int slotNum) {
	return (memAddr + PAGE_SIZE) - (LSN_SIZE + FREE_SPACE_SIZE + NUMSLOTS_SIZE + ((slotNum+1) * SLOT_SIZE));
}

/**
 * pageReadLSN() 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) {
  lsn_t ret;

  readlock(page->rwlatch, 259);
  ret = *(long *)(page->memAddr + START_OF_LSN);
  readunlock(page->rwlatch);

  return ret;
}

/**
 * pageWriteLSN() 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.
 *
 * @param page You must have a writelock on page before calling this function.
 */
static void pageWriteLSN(Page * page) {

  *(long *)(page->memAddr + START_OF_LSN) = page->LSN;
}

static int unlocked_freespace(Page * page);
/**
 * freeSpace() assumes that the page is already loaded in memory.  It takes 
 * as a parameter a Page, and returns an estimate of the amount of free space
 * available to a new slot on this page.  (This is the amount of unused space 
 * in the page, minus the size of a new slot entry.)  This is either exact, 
 * or an underestimate.
 */
int freespace(Page * page) {
  int ret;
  readlock(page->rwlatch, 292);
  ret = unlocked_freespace(page);
  readunlock(page->rwlatch);
  return ret;
}

/** 
    Just like freespace(), but doesn't obtain a lock.  (So that other methods in this file can use it.)
*/
static int unlocked_freespace(Page * page) {
  int space;
  space= (slotMemAddr(page->memAddr, readNumSlots(page->memAddr)) - (page->memAddr + readFreeSpace(page->memAddr)));
  return (space < 0) ? 0 : space;
}

/**
 * readFreeSpace() assumes that the page is already loaded in memory.  It takes
 * as a parameter the memory address of the loaded page in memory and returns
 * the offset at which the free space section of this page begins.
 */
static int readFreeSpace(byte *memAddr) {
	return getSecondHalfOfWord((int*)(memAddr + START_OF_NUMSLOTS));
}

/**
 * writeFreeSpace() assumes that the page is already loaded in memory.  It takes
 * as parameters the memory address of the loaded page in memory and a new offset
 * in the page that will denote the point at which free space begins.
 */
static void writeFreeSpace(byte *memAddr, int newOffset) {
	setSecondHalfOfWord((int*)(memAddr + START_OF_NUMSLOTS), newOffset);
}

/**
 * readNumSlots() assumes that the page is already loaded in memory.  It takes
 * as a parameter the memory address of the loaded page in memory, and returns
 * the memory address at which the free space section of this page begins.
 */
static int readNumSlots(byte *memAddr) {
	return getFirstHalfOfWord((unsigned int*)(memAddr + START_OF_NUMSLOTS));
}

/**
 * writeNumSlots() assumes that the page is already loaded in memory.  It takes
 * as parameters the memory address of the loaded page in memory and an int
 * to which the value of the numSlots field in the page will be set to.
 */
static void writeNumSlots(byte *memAddr, int numSlots) {
	setFirstHalfOfWord((int*)(unsigned int*)(memAddr + START_OF_NUMSLOTS), numSlots);
}

recordid pageRalloc(Page * page, int size) {
        int freeSpace;
        int numSlots;
	int i;

	writelock(page->rwlatch, 342);
	if(unlocked_freespace(page) < size) {
	  
	  pageCompact(page);

	/* Make sure there's enough free space... */

#ifdef DEBUGGING
	  assert (unlocked_freespace(page) >= (int)size); /*Expensive, so skip it when debugging is off. */
#endif

	}
	freeSpace = readFreeSpace(page->memAddr);
	numSlots = readNumSlots(page->memAddr);
	recordid rid;


	rid.page = page->id;
	rid.slot = numSlots;
	rid.size = size;


	/* 
	   Reuse an old (invalid) slot entry.  Why was this here? 
	   
	   @todo is slot reuse in page.c a performance bottleneck? 
	   
	*/
	for (i = 0; i < numSlots; i++) { 
	  if (!isValidSlot(page->memAddr, i)) {
	    rid.slot = i;
	    break;
	  }
	}

	if (rid.slot == numSlots) {
	  writeNumSlots(page->memAddr, numSlots+1);
	}

	setSlotOffset(page->memAddr, rid.slot, freeSpace);
	setSlotLength(page->memAddr, rid.slot, rid.size);  
	writeFreeSpace(page->memAddr, freeSpace + rid.size);

	writeunlock(page->rwlatch);

	/*	DEBUG("slot: %d freespace: %d\n", rid.slot, freeSpace); */

	return rid;
}


/** Only used for recovery, to make sure that consistent RID's are created 
 * on log playback. */
recordid pageSlotRalloc(Page * page, lsn_t lsn, recordid rid) {
        int freeSpace; 
	int numSlots;

	writelock(page->rwlatch, 376);

	freeSpace = readFreeSpace(page->memAddr);
	numSlots= readNumSlots(page->memAddr);

/*	if(rid.size > BLOB_THRESHOLD_SIZE) {
	  return blobSlotAlloc(page, lsn_t lsn, recordid rid);
	  }*/

	/*	assert(rid.slot >= numSlots); */
	if(rid.slot >= numSlots) {

	  if (freeSpace < rid.size) {
	    pageCompact(page);
	    freeSpace = readFreeSpace(page->memAddr);
	    assert (freeSpace < rid.size);
	  }
	  
	  setSlotOffset(page->memAddr, rid.slot, freeSpace);
	  setSlotLength(page->memAddr, rid.slot, rid.size);  
	  writeFreeSpace(page->memAddr, freeSpace + rid.size);
	} else {
	  /*  assert(rid.size == getSlotLength(page.memAddr, rid.slot)); */ /* Fails.  Why? */
	}

	writeunlock(page->rwlatch);

	return rid;
}

int isValidSlot(byte *memAddr, int slot) {
	return (getSlotOffset(memAddr, slot) != INVALID_SLOT) ? 1 : 0;
}

void invalidateSlot(byte *memAddr, int slot) {
	setSlotOffset(memAddr, slot, INVALID_SLOT);
}


void pageDeRalloc(Page * page, recordid rid) {
  writelock(page->rwlatch, 416);
  invalidateSlot(page->memAddr, rid.slot);
  writeunlock(page->rwlatch);
}

/**

 	Move all of the records to the beginning of the page in order to 
	increase the available free space.

	@todo If we were supporting multithreaded operation, this routine 
	      would need to pin the pages that it works on.
*/
static void pageCompact(Page * page) {

	int i;
	byte buffer[PAGE_SIZE];
	int freeSpace = 0;
	int numSlots;
	int meta_size; 
	int slot_length;
	int last_used_slot = -1;

	numSlots = readNumSlots(page->memAddr);

	/*	DEBUG("Compact: numSlots=%d\n", numSlots); */
	meta_size = LSN_SIZE + FREE_SPACE_SIZE + NUMSLOTS_SIZE + (SLOT_SIZE*numSlots);

	/* Can't compact in place, slot numbers can come in different orders than 
	   the physical space allocated to them. */
	memcpy(buffer + PAGE_SIZE - meta_size, page->memAddr + PAGE_SIZE - meta_size, meta_size);

	for (i = 0; i < numSlots; i++) {
	  /*	  DEBUG("i = %d\n", i); */
	          if (isValidSlot(page->memAddr, i)) {
		    /*  		  DEBUG("Buffer offset: %d\n", freeSpace); */
			slot_length = getSlotLength(page->memAddr, i);
			memcpy(buffer + freeSpace, page->memAddr + getSlotOffset(page->memAddr, i), slot_length);
			setSlotOffset(buffer, i, freeSpace);
			freeSpace += slot_length;
			last_used_slot = i;
		} 
	}

	
	/*	if (last_used_slot < numSlots) { */
	writeNumSlots(buffer, last_used_slot + 1);
		/*} */

	/*	DEBUG("freeSpace = %d, num slots = %d\n", freeSpace, last_used_slot + 1); */
	
	writeFreeSpace(buffer, freeSpace);
	
	memcpy(page->memAddr, buffer, PAGE_SIZE);

}

/**
 * getSlotOffset() assumes that the page is already loaded in memory.  It takes
 * as parameters the memory address of the page loaded in memory, and a slot
 * number.  It returns the offset corresponding to that slot.
 */
static int getSlotOffset(byte *memAddr, int slot) {
	return getFirstHalfOfWord((unsigned int*)slotMemAddr(memAddr, slot));
}

/**
 * getSlotLength() assumes that the page is already loaded in memory.  It takes
 * as parameters the memory address of the page loaded in memory, and a slot
 * number.  It returns the length corresponding to that slot.
 */
static int getSlotLength(byte *memAddr, int slot) {
	return getSecondHalfOfWord((int*)(unsigned int*)slotMemAddr(memAddr, slot));
}

/**
 * setSlotOffset() assumes that the page is already loaded in memory.  It takes
 * as parameters the memory address of the page loaded in memory, a slot number,
 * and an offset.  It sets the offset of the given slot to the offset passed in
 * as a parameter.
 */
static void setSlotOffset(byte *memAddr, int slot, int offset) {
	setFirstHalfOfWord((int*)slotMemAddr(memAddr, slot), offset);
}

/**
 * setSlotLength() assumes that the page is already loaded in memory.  It takes
 * as parameters the memory address of the page loaded in memory, a slot number,
 * and a length.  It sets the length of the given slot to the length passed in
 * as a parameter.
 */
static void setSlotLength(byte *memAddr, int slot, int length) {
	setSecondHalfOfWord((int*)(unsigned int*)slotMemAddr(memAddr, slot), length);
}

int isBlobSlot(byte *pageMemAddr, int slot) {
	return BLOB_SLOT == getSlotLength(pageMemAddr, slot);
}

/*
  This needs should trust the rid (since the caller needs to
  override the size in special circumstances)

  @todo If the rid size has been overridden, we should check to make
  sure that this really is a special record.
*/
void pageReadRecord(int xid, Page * page, recordid rid, byte *buff) {
  byte *recAddress;
  
  readlock(page->rwlatch, 519);
  recAddress = page->memAddr + getSlotOffset(page->memAddr, rid.slot);
  memcpy(buff, recAddress,  rid.size);
  readunlock(page->rwlatch);
  
}

void pageWriteRecord(int xid, Page * page, recordid rid, lsn_t lsn, const byte *data) {

  byte *rec; 
  readlock(page->rwlatch, 529);
  assert(rid.size < PAGE_SIZE);
  
  rec = page->memAddr + getSlotOffset(page->memAddr, rid.slot);
  
  if(memcpy(rec, data,  rid.size) == NULL ) {
    printf("ERROR: MEM_WRITE_ERROR on %s line %d", __FILE__, __LINE__);
    exit(MEM_WRITE_ERROR);
  }

  page->LSN = lsn;
  pageWriteLSN(page);
  readunlock(page->rwlatch);

}

void pageRealloc(Page *p, int id) {
  writelock(p->rwlatch, 10);
  p->id = id;
  p->LSN = 0;
  p->dirty = 0;
  p->pending = 0;
  p->waiting = 0;
  writeunlock(p->rwlatch);
}


/** 
	Allocate a new page. 
        @param id The id of the new page.
	@return A pointer to the new page.  This memory is part of a pool, 
	        and should never be freed manually.
 */
Page *pageAlloc(int id) {
  Page *page;

  pthread_mutex_lock(&pageAllocMutex);
  
  page = &(pool[nextPage]);
  
  /* We have an implicit lock on rwlatch, since we allocated it, but
     haven't returned yet. */
  page->rwlatch = initlock();

  pthread_mutex_init(&page->pending_mutex, NULL);
  pthread_cond_init(&page->noMorePending, NULL);

  nextPage++;
  assert(nextPage <= MAX_BUFFER_SIZE);

  /* uggh.  Really just want to pass pages by reference */
  /*  page->pending = malloc(sizeof(int));  */

  pthread_mutex_unlock(&pageAllocMutex);


  /* pageRealloc does its own locking... */
  pageRealloc(page, id);
  

  return page;
}

void printPage(byte *memAddr) {
	int i = 0;
	for (i = 0; i < PAGE_SIZE; i++) {
		if((*(char *)(memAddr+i)) == 0) {
			printf("#");
		}else {
			printf("%c", *(char *)(memAddr+i));
		}
		if((i+1)%4 == 0)
			printf(" ");
	}
}

#define num 20
int pageTest() {

        Page * page = malloc(sizeof(Page));

	recordid rid[num];
	char *str[num] = {"one",
		"two",
		"three",
		"four",
		"five",
		"six",
		"seven",
		"eight",
		"nine",
		"ten",
		"eleven",
		"twelve",
		"thirteen",
		"fourteen",
		"fifteen",
		"sixteen",
		"seventeen",
		"eighteen",
		"nineteen",
		"twenty"};
		int i;

		page->memAddr = (byte *)malloc(PAGE_SIZE);
		memset(page->memAddr, 0, PAGE_SIZE);
		for (i = 0; i < num; i++) {
			rid[i] = pageRalloc(page, strlen(str[i]) + 1);
			pageWriteRecord(0, page, rid[i], 1, (byte*)str[i]);    
		}
		printPage(page->memAddr);

		for (i = 0; i < num; i+= 2)
			pageDeRalloc(page, rid[i]);

		pageCompact(page);
		printf("\n\n\n");
		printPage(page->memAddr);
		return 0;
}

void pageSetSlotType(Page * p, int slot, int type) {
  assert(type > PAGE_SIZE);
  
  /* setSlotLength does the locking for us. */
  setSlotLength(p->memAddr, slot, type);

}

int pageGetSlotType(Page *  p, int slot, int type) {
  int ret = getSlotLength(p->memAddr, slot);
  /* getSlotType does the locking for us. */
  return ret > PAGE_SIZE ? ret : NORMAL_SLOT;
}