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

/*---
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---*/
/************************************************
 * $Id$
 *
 * implementation of pages
 ************************************************/

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <lladd/bufferManager.h>
#include <lladd/constants.h>
/*#include "linkedlist.h"*/
#include <lladd/page.h>
#include <pbl/pbl.h>

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


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

 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)

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

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) ;

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;


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

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;

}

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.
 */
long pageReadLSN(Page page) {
	return *(long *)(page.memAddr + START_OF_LSN);
}

/**
 * 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.
 */
void pageWriteLSN(Page page) {
	*(long *)(page.memAddr + START_OF_LSN) = page.LSN;
}

/**
 * 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.
 */
size_t freespace(Page page) {
	int 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);
}

/**
 * pageRalloc() assumes that the page is already loaded in memory.  It takes
 * as parameters a Page and the size in bytes of the new record.  pageRalloc()
 * returns a recordid representing the newly allocated record.
 *
 * NOTE: might want to pad records to be multiple of words in length, or, simply
 *       make sure all records start word aligned, but not necessarily having 
 *       a length that is a multiple of words.  (Since Tread(), Twrite() ultimately 
 *       call memcpy(), this shouldn't be an issue)
 *
 * NOTE: pageRalloc() assumes that the caller already made sure that sufficient
 * amount of freespace exists in this page.  (@see freespace())
 *
 * @todo Makes no attempt to reuse old recordid's.
 */
recordid pageRalloc(Page page, size_t size) {
	int freeSpace = readFreeSpace(page.memAddr);
	int numSlots = readNumSlots(page.memAddr);
	recordid rid;

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

	/* Make sure there's enough free space... */
	/*	assert (freespace(page) >= (int)size); */ /*Expensive, so skipped not done. */

	/* Reuse an old (invalid) slot entry.  Why was this here? */
	/*	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);

	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 = readFreeSpace(page.memAddr);
	int 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? */
	}
	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) {
	invalidateSlot(page.memAddr, rid.slot);
}

/**

 	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.
*/
void pageCompact(Page page) {

	int i;
	byte buffer[PAGE_SIZE];
	int freeSpace = 0;
	int numSlots = readNumSlots(page.memAddr);
	int meta_size = LSN_SIZE + FREE_SPACE_SIZE + NUMSLOTS_SIZE + (SLOT_SIZE*numSlots);
	int slot_length;
	int last_used_slot = 0;

	/* 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++) {
		if (isValidSlot(page.memAddr, i)) {
			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);
	}

	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);
}

/*
  @todo This needs should trust the rid (since the caller needs to
  overrid the size in special circumstances, but if the size has been
  overridden, we should check for the circumstances where doing so is
  allowed. 
*/
void pageReadRecord(int xid, Page page, recordid rid, byte *buff) {

  byte *recAddress = page.memAddr + getSlotOffset(page.memAddr, rid.slot);
  memcpy(buff, recAddress,  rid.size);

}

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

  byte *rec; 
  
  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);
  }

}

void pageRealloc(Page *p, int id) {
	p->id = id;
	p->LSN = 0;
	p->dirty = 0;
}

Page pool[MAX_BUFFER_SIZE];

/** 
	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 by manually.
 */
Page *pageAlloc(int id) {
  Page *p = &(pool[nextPage]);

  nextPage++;

  assert(nextPage <= MAX_BUFFER_SIZE);
  pageRealloc(p, id);

  return p;
}

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;

	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], (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 setSlotType(Page p, int slot, int type) {

  assert(type > PAGE_SIZE);

  setSlotLength(p.memAddr, slot, type);

}

int getSlotType(Page p, int slot, int type) {
  int ret = getSlotLength(p.memAddr, slot);

  return ret > PAGE_SIZE ? ret : NORMAL_SLOT;
}