Revert dubious message wording change.

[PostgreSQL.git] / src / backend / utils / mmgr / aset.c

/*-------------------------------------------------------------------------
 *
 * aset.c
 *        Allocation set definitions.
 *
 * AllocSet is our standard implementation of the abstract MemoryContext
 * type.
 *
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        $PostgreSQL$
 *
 * NOTE:
 *      This is a new (Feb. 05, 1999) implementation of the allocation set
 *      routines. AllocSet...() does not use OrderedSet...() any more.
 *      Instead it manages allocations in a block pool by itself, combining
 *      many small allocations in a few bigger blocks. AllocSetFree() normally
 *      doesn't free() memory really. It just add's the free'd area to some
 *      list for later reuse by AllocSetAlloc(). All memory blocks are free()'d
 *      at once on AllocSetReset(), which happens when the memory context gets
 *      destroyed.
 *                              Jan Wieck
 *
 *      Performance improvement from Tom Lane, 8/99: for extremely large request
 *      sizes, we do want to be able to give the memory back to free() as soon
 *      as it is pfree()'d.  Otherwise we risk tying up a lot of memory in
 *      freelist entries that might never be usable.  This is specially needed
 *      when the caller is repeatedly repalloc()'ing a block bigger and bigger;
 *      the previous instances of the block were guaranteed to be wasted until
 *      AllocSetReset() under the old way.
 *
 *      Further improvement 12/00: as the code stood, request sizes in the
 *      midrange between "small" and "large" were handled very inefficiently,
 *      because any sufficiently large free chunk would be used to satisfy a
 *      request, even if it was much larger than necessary.  This led to more
 *      and more wasted space in allocated chunks over time.  To fix, get rid
 *      of the midrange behavior: we now handle only "small" power-of-2-size
 *      chunks as chunks.  Anything "large" is passed off to malloc().  Change
 *      the number of freelists to change the small/large boundary.
 *
 *
 *      About CLOBBER_FREED_MEMORY:
 *
 *      If this symbol is defined, all freed memory is overwritten with 0x7F's.
 *      This is useful for catching places that reference already-freed memory.
 *
 *      About MEMORY_CONTEXT_CHECKING:
 *
 *      Since we usually round request sizes up to the next power of 2, there
 *      is often some unused space immediately after a requested data area.
 *      Thus, if someone makes the common error of writing past what they've
 *      requested, the problem is likely to go unnoticed ... until the day when
 *      there *isn't* any wasted space, perhaps because of different memory
 *      alignment on a new platform, or some other effect.      To catch this sort
 *      of problem, the MEMORY_CONTEXT_CHECKING option stores 0x7E just beyond
 *      the requested space whenever the request is less than the actual chunk
 *      size, and verifies that the byte is undamaged when the chunk is freed.
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "utils/memutils.h"

/* Define this to detail debug alloc information */
/* #define HAVE_ALLOCINFO */

/*--------------------
 * Chunk freelist k holds chunks of size 1 << (k + ALLOC_MINBITS),
 * for k = 0 .. ALLOCSET_NUM_FREELISTS-1.
 *
 * Note that all chunks in the freelists have power-of-2 sizes.  This
 * improves recyclability: we may waste some space, but the wasted space
 * should stay pretty constant as requests are made and released.
 *
 * A request too large for the last freelist is handled by allocating a
 * dedicated block from malloc().  The block still has a block header and
 * chunk header, but when the chunk is freed we'll return the whole block
 * to malloc(), not put it on our freelists.
 *
 * CAUTION: ALLOC_MINBITS must be large enough so that
 * 1<<ALLOC_MINBITS is at least MAXALIGN,
 * or we may fail to align the smallest chunks adequately.
 * 8-byte alignment is enough on all currently known machines.
 *
 * With the current parameters, request sizes up to 8K are treated as chunks,
 * larger requests go into dedicated blocks.  Change ALLOCSET_NUM_FREELISTS
 * to adjust the boundary point.
 *--------------------
 */

#define ALLOC_MINBITS           3       /* smallest chunk size is 8 bytes */
#define ALLOCSET_NUM_FREELISTS  11
#define ALLOC_CHUNK_LIMIT       (1 << (ALLOCSET_NUM_FREELISTS-1+ALLOC_MINBITS))
/* Size of largest chunk that we use a fixed size for */

/*--------------------
 * The first block allocated for an allocset has size initBlockSize.
 * Each time we have to allocate another block, we double the block size
 * (if possible, and without exceeding maxBlockSize), so as to reduce
 * the bookkeeping load on malloc().
 *
 * Blocks allocated to hold oversize chunks do not follow this rule, however;
 * they are just however big they need to be to hold that single chunk.
 *--------------------
 */

#define ALLOC_BLOCKHDRSZ        MAXALIGN(sizeof(AllocBlockData))
#define ALLOC_CHUNKHDRSZ        MAXALIGN(sizeof(AllocChunkData))

typedef struct AllocBlockData *AllocBlock;              /* forward reference */
typedef struct AllocChunkData *AllocChunk;

/*
 * AllocPointer
 *              Aligned pointer which may be a member of an allocation set.
 */
typedef void *AllocPointer;

/*
 * AllocSetContext is our standard implementation of MemoryContext.
 *
 * Note: isReset means there is nothing for AllocSetReset to do.  This is
 * different from the aset being physically empty (empty blocks list) because
 * we may still have a keeper block.  It's also different from the set being
 * logically empty, because we don't attempt to detect pfree'ing the last
 * active chunk.
 */
typedef struct AllocSetContext
{
        MemoryContextData header;       /* Standard memory-context fields */
        /* Info about storage allocated in this context: */
        AllocBlock      blocks;                 /* head of list of blocks in this set */
        AllocChunk      freelist[ALLOCSET_NUM_FREELISTS];               /* free chunk lists */
        bool            isReset;                /* T = no space alloced since last reset */
        /* Allocation parameters for this context: */
        Size            initBlockSize;  /* initial block size */
        Size            maxBlockSize;   /* maximum block size */
        Size            nextBlockSize;  /* next block size to allocate */
        Size            allocChunkLimit;        /* effective chunk size limit */
        AllocBlock      keeper;                 /* if not NULL, keep this block over resets */
} AllocSetContext;

typedef AllocSetContext *AllocSet;

/*
 * AllocBlock
 *              An AllocBlock is the unit of memory that is obtained by aset.c
 *              from malloc().  It contains one or more AllocChunks, which are
 *              the units requested by palloc() and freed by pfree().  AllocChunks
 *              cannot be returned to malloc() individually, instead they are put
 *              on freelists by pfree() and re-used by the next palloc() that has
 *              a matching request size.
 *
 *              AllocBlockData is the header data for a block --- the usable space
 *              within the block begins at the next alignment boundary.
 */
typedef struct AllocBlockData
{
        AllocSet        aset;                   /* aset that owns this block */
        AllocBlock      next;                   /* next block in aset's blocks list */
        char       *freeptr;            /* start of free space in this block */
        char       *endptr;                     /* end of space in this block */
} AllocBlockData;

/*
 * AllocChunk
 *              The prefix of each piece of memory in an AllocBlock
 *
 * NB: this MUST match StandardChunkHeader as defined by utils/memutils.h.
 */
typedef struct AllocChunkData
{
        /* aset is the owning aset if allocated, or the freelist link if free */
        void       *aset;
        /* size is always the size of the usable space in the chunk */
        Size            size;
#ifdef MEMORY_CONTEXT_CHECKING
        /* when debugging memory usage, also store actual requested size */
        /* this is zero in a free chunk */
        Size            requested_size;
#endif
} AllocChunkData;

/*
 * AllocPointerIsValid
 *              True iff pointer is valid allocation pointer.
 */
#define AllocPointerIsValid(pointer) PointerIsValid(pointer)

/*
 * AllocSetIsValid
 *              True iff set is valid allocation set.
 */
#define AllocSetIsValid(set) PointerIsValid(set)

#define AllocPointerGetChunk(ptr)       \
                                        ((AllocChunk)(((char *)(ptr)) - ALLOC_CHUNKHDRSZ))
#define AllocChunkGetPointer(chk)       \
                                        ((AllocPointer)(((char *)(chk)) + ALLOC_CHUNKHDRSZ))

/*
 * These functions implement the MemoryContext API for AllocSet contexts.
 */
static void *AllocSetAlloc(MemoryContext context, Size size);
static void AllocSetFree(MemoryContext context, void *pointer);
static void *AllocSetRealloc(MemoryContext context, void *pointer, Size size);
static void AllocSetInit(MemoryContext context);
static void AllocSetReset(MemoryContext context);
static void AllocSetDelete(MemoryContext context);
static Size AllocSetGetChunkSpace(MemoryContext context, void *pointer);
static bool AllocSetIsEmpty(MemoryContext context);
static void AllocSetStats(MemoryContext context, int level);

#ifdef MEMORY_CONTEXT_CHECKING
static void AllocSetCheck(MemoryContext context);
#endif

/*
 * This is the virtual function table for AllocSet contexts.
 */
static MemoryContextMethods AllocSetMethods = {
        AllocSetAlloc,
        AllocSetFree,
        AllocSetRealloc,
        AllocSetInit,
        AllocSetReset,
        AllocSetDelete,
        AllocSetGetChunkSpace,
        AllocSetIsEmpty,
        AllocSetStats
#ifdef MEMORY_CONTEXT_CHECKING
        ,AllocSetCheck
#endif
};


/* ----------
 * Debug macros
 * ----------
 */
#ifdef HAVE_ALLOCINFO
#define AllocFreeInfo(_cxt, _chunk) \
                        fprintf(stderr, "AllocFree: %s: %p, %d\n", \
                                (_cxt)->header.name, (_chunk), (_chunk)->size)
#define AllocAllocInfo(_cxt, _chunk) \
                        fprintf(stderr, "AllocAlloc: %s: %p, %d\n", \
                                (_cxt)->header.name, (_chunk), (_chunk)->size)
#else
#define AllocFreeInfo(_cxt, _chunk)
#define AllocAllocInfo(_cxt, _chunk)
#endif

/* ----------
 * AllocSetFreeIndex -
 *
 *              Depending on the size of an allocation compute which freechunk
 *              list of the alloc set it belongs to.  Caller must have verified
 *              that size <= ALLOC_CHUNK_LIMIT.
 * ----------
 */
static inline int
AllocSetFreeIndex(Size size)
{
        int                     idx = 0;

        if (size > 0)
        {
                size = (size - 1) >> ALLOC_MINBITS;
                while (size != 0)
                {
                        idx++;
                        size >>= 1;
                }
                Assert(idx < ALLOCSET_NUM_FREELISTS);
        }

        return idx;
}

#ifdef RANDOMIZE_ALLOCATED_MEMORY

/*
 * Fill a just-allocated piece of memory with "random" data.  It's not really
 * very random, just a repeating sequence with a length that's prime.  What
 * we mainly want out of it is to have a good probability that two palloc's
 * of the same number of bytes start out containing different data.
 */
static void
randomize_mem(char *ptr, size_t size)
{
        static int      save_ctr = 1;
        int                     ctr;

        ctr = save_ctr;
        while (size-- > 0)
        {
                *ptr++ = ctr;
                if (++ctr > 251)
                        ctr = 1;
        }
        save_ctr = ctr;
}
#endif   /* RANDOMIZE_ALLOCATED_MEMORY */


/*
 * Public routines
 */


/*
 * AllocSetContextCreate
 *              Create a new AllocSet context.
 *
 * parent: parent context, or NULL if top-level context
 * name: name of context (for debugging --- string will be copied)
 * minContextSize: minimum context size
 * initBlockSize: initial allocation block size
 * maxBlockSize: maximum allocation block size
 */
MemoryContext
AllocSetContextCreate(MemoryContext parent,
                                          const char *name,
                                          Size minContextSize,
                                          Size initBlockSize,
                                          Size maxBlockSize)
{
        AllocSet        context;

        /* Do the type-independent part of context creation */
        context = (AllocSet) MemoryContextCreate(T_AllocSetContext,
                                                                                         sizeof(AllocSetContext),
                                                                                         &AllocSetMethods,
                                                                                         parent,
                                                                                         name);

        /*
         * Make sure alloc parameters are reasonable, and save them.
         *
         * We somewhat arbitrarily enforce a minimum 1K block size.
         */
        initBlockSize = MAXALIGN(initBlockSize);
        if (initBlockSize < 1024)
                initBlockSize = 1024;
        maxBlockSize = MAXALIGN(maxBlockSize);
        if (maxBlockSize < initBlockSize)
                maxBlockSize = initBlockSize;
        context->initBlockSize = initBlockSize;
        context->maxBlockSize = maxBlockSize;
        context->nextBlockSize = initBlockSize;

        /*
         * Compute the allocation chunk size limit for this context.  It can't be
         * more than ALLOC_CHUNK_LIMIT because of the fixed number of freelists.
         * If maxBlockSize is small then requests exceeding the maxBlockSize
         * should be treated as large chunks, too.      We have to have
         * allocChunkLimit a power of two, because the requested and
         * actually-allocated sizes of any chunk must be on the same side of the
         * limit, else we get confused about whether the chunk is "big".
         */
        context->allocChunkLimit = ALLOC_CHUNK_LIMIT;
        while (context->allocChunkLimit >
                   (Size) (maxBlockSize - ALLOC_BLOCKHDRSZ - ALLOC_CHUNKHDRSZ))
                context->allocChunkLimit >>= 1;

        /*
         * Grab always-allocated space, if requested
         */
        if (minContextSize > ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ)
        {
                Size            blksize = MAXALIGN(minContextSize);
                AllocBlock      block;

                block = (AllocBlock) malloc(blksize);
                if (block == NULL)
                {
                        MemoryContextStats(TopMemoryContext);
                        ereport(ERROR,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory"),
                                         errdetail("Failed while creating memory context \"%s\".",
                                                           name)));
                }
                block->aset = context;
                block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
                block->endptr = ((char *) block) + blksize;
                block->next = context->blocks;
                context->blocks = block;
                /* Mark block as not to be released at reset time */
                context->keeper = block;
        }

        context->isReset = true;

        return (MemoryContext) context;
}

/*
 * AllocSetInit
 *              Context-type-specific initialization routine.
 *
 * This is called by MemoryContextCreate() after setting up the
 * generic MemoryContext fields and before linking the new context
 * into the context tree.  We must do whatever is needed to make the
 * new context minimally valid for deletion.  We must *not* risk
 * failure --- thus, for example, allocating more memory is not cool.
 * (AllocSetContextCreate can allocate memory when it gets control
 * back, however.)
 */
static void
AllocSetInit(MemoryContext context)
{
        /*
         * Since MemoryContextCreate already zeroed the context node, we don't
         * have to do anything here: it's already OK.
         */
}

/*
 * AllocSetReset
 *              Frees all memory which is allocated in the given set.
 *
 * Actually, this routine has some discretion about what to do.
 * It should mark all allocated chunks freed, but it need not necessarily
 * give back all the resources the set owns.  Our actual implementation is
 * that we hang onto any "keeper" block specified for the set.  In this way,
 * we don't thrash malloc() when a context is repeatedly reset after small
 * allocations, which is typical behavior for per-tuple contexts.
 */
static void
AllocSetReset(MemoryContext context)
{
        AllocSet        set = (AllocSet) context;
        AllocBlock      block;

        AssertArg(AllocSetIsValid(set));

        /* Nothing to do if no pallocs since startup or last reset */
        if (set->isReset)
                return;

#ifdef MEMORY_CONTEXT_CHECKING
        /* Check for corruption and leaks before freeing */
        AllocSetCheck(context);
#endif

        /* Clear chunk freelists */
        MemSetAligned(set->freelist, 0, sizeof(set->freelist));

        block = set->blocks;

        /* New blocks list is either empty or just the keeper block */
        set->blocks = set->keeper;

        while (block != NULL)
        {
                AllocBlock      next = block->next;

                if (block == set->keeper)
                {
                        /* Reset the block, but don't return it to malloc */
                        char       *datastart = ((char *) block) + ALLOC_BLOCKHDRSZ;

#ifdef CLOBBER_FREED_MEMORY
                        /* Wipe freed memory for debugging purposes */
                        memset(datastart, 0x7F, block->freeptr - datastart);
#endif
                        block->freeptr = datastart;
                        block->next = NULL;
                }
                else
                {
                        /* Normal case, release the block */
#ifdef CLOBBER_FREED_MEMORY
                        /* Wipe freed memory for debugging purposes */
                        memset(block, 0x7F, block->freeptr - ((char *) block));
#endif
                        free(block);
                }
                block = next;
        }

        /* Reset block size allocation sequence, too */
        set->nextBlockSize = set->initBlockSize;

        set->isReset = true;
}

/*
 * AllocSetDelete
 *              Frees all memory which is allocated in the given set,
 *              in preparation for deletion of the set.
 *
 * Unlike AllocSetReset, this *must* free all resources of the set.
 * But note we are not responsible for deleting the context node itself.
 */
static void
AllocSetDelete(MemoryContext context)
{
        AllocSet        set = (AllocSet) context;
        AllocBlock      block = set->blocks;

        AssertArg(AllocSetIsValid(set));

#ifdef MEMORY_CONTEXT_CHECKING
        /* Check for corruption and leaks before freeing */
        AllocSetCheck(context);
#endif

        /* Make it look empty, just in case... */
        MemSetAligned(set->freelist, 0, sizeof(set->freelist));
        set->blocks = NULL;
        set->keeper = NULL;

        while (block != NULL)
        {
                AllocBlock      next = block->next;

#ifdef CLOBBER_FREED_MEMORY
                /* Wipe freed memory for debugging purposes */
                memset(block, 0x7F, block->freeptr - ((char *) block));
#endif
                free(block);
                block = next;
        }
}

/*
 * AllocSetAlloc
 *              Returns pointer to allocated memory of given size; memory is added
 *              to the set.
 */
static void *
AllocSetAlloc(MemoryContext context, Size size)
{
        AllocSet        set = (AllocSet) context;
        AllocBlock      block;
        AllocChunk      chunk;
        int                     fidx;
        Size            chunk_size;
        Size            blksize;

        AssertArg(AllocSetIsValid(set));

        /*
         * If requested size exceeds maximum for chunks, allocate an entire block
         * for this request.
         */
        if (size > set->allocChunkLimit)
        {
                chunk_size = MAXALIGN(size);
                blksize = chunk_size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
                block = (AllocBlock) malloc(blksize);
                if (block == NULL)
                {
                        MemoryContextStats(TopMemoryContext);
                        ereport(ERROR,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory"),
                                         errdetail("Failed on request of size %lu.",
                                                           (unsigned long) size)));
                }
                block->aset = set;
                block->freeptr = block->endptr = ((char *) block) + blksize;

                chunk = (AllocChunk) (((char *) block) + ALLOC_BLOCKHDRSZ);
                chunk->aset = set;
                chunk->size = chunk_size;
#ifdef MEMORY_CONTEXT_CHECKING
                chunk->requested_size = size;
                /* set mark to catch clobber of "unused" space */
                if (size < chunk_size)
                        ((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
#endif
#ifdef RANDOMIZE_ALLOCATED_MEMORY
                /* fill the allocated space with junk */
                randomize_mem((char *) AllocChunkGetPointer(chunk), size);
#endif

                /*
                 * Stick the new block underneath the active allocation block, so that
                 * we don't lose the use of the space remaining therein.
                 */
                if (set->blocks != NULL)
                {
                        block->next = set->blocks->next;
                        set->blocks->next = block;
                }
                else
                {
                        block->next = NULL;
                        set->blocks = block;
                }

                set->isReset = false;

                AllocAllocInfo(set, chunk);
                return AllocChunkGetPointer(chunk);
        }

        /*
         * Request is small enough to be treated as a chunk.  Look in the
         * corresponding free list to see if there is a free chunk we could reuse.
         * If one is found, remove it from the free list, make it again a member
         * of the alloc set and return its data address.
         */
        fidx = AllocSetFreeIndex(size);
        chunk = set->freelist[fidx];
        if (chunk != NULL)
        {
                Assert(chunk->size >= size);

                set->freelist[fidx] = (AllocChunk) chunk->aset;

                chunk->aset = (void *) set;

#ifdef MEMORY_CONTEXT_CHECKING
                chunk->requested_size = size;
                /* set mark to catch clobber of "unused" space */
                if (size < chunk->size)
                        ((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
#endif
#ifdef RANDOMIZE_ALLOCATED_MEMORY
                /* fill the allocated space with junk */
                randomize_mem((char *) AllocChunkGetPointer(chunk), size);
#endif

                /* isReset must be false already */
                Assert(!set->isReset);

                AllocAllocInfo(set, chunk);
                return AllocChunkGetPointer(chunk);
        }

        /*
         * Choose the actual chunk size to allocate.
         */
        chunk_size = (1 << ALLOC_MINBITS) << fidx;
        Assert(chunk_size >= size);

        /*
         * If there is enough room in the active allocation block, we will put the
         * chunk into that block.  Else must start a new one.
         */
        if ((block = set->blocks) != NULL)
        {
                Size            availspace = block->endptr - block->freeptr;

                if (availspace < (chunk_size + ALLOC_CHUNKHDRSZ))
                {
                        /*
                         * The existing active (top) block does not have enough room for
                         * the requested allocation, but it might still have a useful
                         * amount of space in it.  Once we push it down in the block list,
                         * we'll never try to allocate more space from it. So, before we
                         * do that, carve up its free space into chunks that we can put on
                         * the set's freelists.
                         *
                         * Because we can only get here when there's less than
                         * ALLOC_CHUNK_LIMIT left in the block, this loop cannot iterate
                         * more than ALLOCSET_NUM_FREELISTS-1 times.
                         */
                        while (availspace >= ((1 << ALLOC_MINBITS) + ALLOC_CHUNKHDRSZ))
                        {
                                Size            availchunk = availspace - ALLOC_CHUNKHDRSZ;
                                int                     a_fidx = AllocSetFreeIndex(availchunk);

                                /*
                                 * In most cases, we'll get back the index of the next larger
                                 * freelist than the one we need to put this chunk on.  The
                                 * exception is when availchunk is exactly a power of 2.
                                 */
                                if (availchunk != (1 << (a_fidx + ALLOC_MINBITS)))
                                {
                                        a_fidx--;
                                        Assert(a_fidx >= 0);
                                        availchunk = (1 << (a_fidx + ALLOC_MINBITS));
                                }

                                chunk = (AllocChunk) (block->freeptr);

                                block->freeptr += (availchunk + ALLOC_CHUNKHDRSZ);
                                availspace -= (availchunk + ALLOC_CHUNKHDRSZ);

                                chunk->size = availchunk;
#ifdef MEMORY_CONTEXT_CHECKING
                                chunk->requested_size = 0;              /* mark it free */
#endif
                                chunk->aset = (void *) set->freelist[a_fidx];
                                set->freelist[a_fidx] = chunk;
                        }

                        /* Mark that we need to create a new block */
                        block = NULL;
                }
        }

        /*
         * Time to create a new regular (multi-chunk) block?
         */
        if (block == NULL)
        {
                Size            required_size;

                /*
                 * The first such block has size initBlockSize, and we double the
                 * space in each succeeding block, but not more than maxBlockSize.
                 */
                blksize = set->nextBlockSize;
                set->nextBlockSize <<= 1;
                if (set->nextBlockSize > set->maxBlockSize)
                        set->nextBlockSize = set->maxBlockSize;

                /*
                 * If initBlockSize is less than ALLOC_CHUNK_LIMIT, we could need more
                 * space... but try to keep it a power of 2.
                 */
                required_size = chunk_size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
                while (blksize < required_size)
                        blksize <<= 1;

                /* Try to allocate it */
                block = (AllocBlock) malloc(blksize);

                /*
                 * We could be asking for pretty big blocks here, so cope if malloc
                 * fails.  But give up if there's less than a meg or so available...
                 */
                while (block == NULL && blksize > 1024 * 1024)
                {
                        blksize >>= 1;
                        if (blksize < required_size)
                                break;
                        block = (AllocBlock) malloc(blksize);
                }

                if (block == NULL)
                {
                        MemoryContextStats(TopMemoryContext);
                        ereport(ERROR,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory"),
                                         errdetail("Failed on request of size %lu.",
                                                           (unsigned long) size)));
                }

                block->aset = set;
                block->freeptr = ((char *) block) + ALLOC_BLOCKHDRSZ;
                block->endptr = ((char *) block) + blksize;

                /*
                 * If this is the first block of the set, make it the "keeper" block.
                 * Formerly, a keeper block could only be created during context
                 * creation, but allowing it to happen here lets us have fast reset
                 * cycling even for contexts created with minContextSize = 0; that way
                 * we don't have to force space to be allocated in contexts that might
                 * never need any space.  Don't mark an oversize block as a keeper,
                 * however.
                 */
                if (set->keeper == NULL && blksize == set->initBlockSize)
                        set->keeper = block;

                block->next = set->blocks;
                set->blocks = block;
        }

        /*
         * OK, do the allocation
         */
        chunk = (AllocChunk) (block->freeptr);

        block->freeptr += (chunk_size + ALLOC_CHUNKHDRSZ);
        Assert(block->freeptr <= block->endptr);

        chunk->aset = (void *) set;
        chunk->size = chunk_size;
#ifdef MEMORY_CONTEXT_CHECKING
        chunk->requested_size = size;
        /* set mark to catch clobber of "unused" space */
        if (size < chunk->size)
                ((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
#endif
#ifdef RANDOMIZE_ALLOCATED_MEMORY
        /* fill the allocated space with junk */
        randomize_mem((char *) AllocChunkGetPointer(chunk), size);
#endif

        set->isReset = false;

        AllocAllocInfo(set, chunk);
        return AllocChunkGetPointer(chunk);
}

/*
 * AllocSetFree
 *              Frees allocated memory; memory is removed from the set.
 */
static void
AllocSetFree(MemoryContext context, void *pointer)
{
        AllocSet        set = (AllocSet) context;
        AllocChunk      chunk = AllocPointerGetChunk(pointer);

        AllocFreeInfo(set, chunk);

#ifdef MEMORY_CONTEXT_CHECKING
        /* Test for someone scribbling on unused space in chunk */
        if (chunk->requested_size < chunk->size)
                if (((char *) pointer)[chunk->requested_size] != 0x7E)
                        elog(WARNING, "detected write past chunk end in %s %p",
                                 set->header.name, chunk);
#endif

        if (chunk->size > set->allocChunkLimit)
        {
                /*
                 * Big chunks are certain to have been allocated as single-chunk
                 * blocks.      Find the containing block and return it to malloc().
                 */
                AllocBlock      block = set->blocks;
                AllocBlock      prevblock = NULL;

                while (block != NULL)
                {
                        if (chunk == (AllocChunk) (((char *) block) + ALLOC_BLOCKHDRSZ))
                                break;
                        prevblock = block;
                        block = block->next;
                }
                if (block == NULL)
                        elog(ERROR, "could not find block containing chunk %p", chunk);
                /* let's just make sure chunk is the only one in the block */
                Assert(block->freeptr == ((char *) block) +
                           (chunk->size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ));

                /* OK, remove block from aset's list and free it */
                if (prevblock == NULL)
                        set->blocks = block->next;
                else
                        prevblock->next = block->next;
#ifdef CLOBBER_FREED_MEMORY
                /* Wipe freed memory for debugging purposes */
                memset(block, 0x7F, block->freeptr - ((char *) block));
#endif
                free(block);
        }
        else
        {
                /* Normal case, put the chunk into appropriate freelist */
                int                     fidx = AllocSetFreeIndex(chunk->size);

                chunk->aset = (void *) set->freelist[fidx];

#ifdef CLOBBER_FREED_MEMORY
                /* Wipe freed memory for debugging purposes */
                memset(pointer, 0x7F, chunk->size);
#endif

#ifdef MEMORY_CONTEXT_CHECKING
                /* Reset requested_size to 0 in chunks that are on freelist */
                chunk->requested_size = 0;
#endif
                set->freelist[fidx] = chunk;
        }
}

/*
 * AllocSetRealloc
 *              Returns new pointer to allocated memory of given size; this memory
 *              is added to the set.  Memory associated with given pointer is copied
 *              into the new memory, and the old memory is freed.
 */
static void *
AllocSetRealloc(MemoryContext context, void *pointer, Size size)
{
        AllocSet        set = (AllocSet) context;
        AllocChunk      chunk = AllocPointerGetChunk(pointer);
        Size            oldsize = chunk->size;

#ifdef MEMORY_CONTEXT_CHECKING
        /* Test for someone scribbling on unused space in chunk */
        if (chunk->requested_size < oldsize)
                if (((char *) pointer)[chunk->requested_size] != 0x7E)
                        elog(WARNING, "detected write past chunk end in %s %p",
                                 set->header.name, chunk);
#endif

        /* isReset must be false already */
        Assert(!set->isReset);

        /*
         * Chunk sizes are aligned to power of 2 in AllocSetAlloc(). Maybe the
         * allocated area already is >= the new size.  (In particular, we always
         * fall out here if the requested size is a decrease.)
         */
        if (oldsize >= size)
        {
#ifdef MEMORY_CONTEXT_CHECKING
#ifdef RANDOMIZE_ALLOCATED_MEMORY
                /* We can only fill the extra space if we know the prior request */
                if (size > chunk->requested_size)
                        randomize_mem((char *) AllocChunkGetPointer(chunk) + chunk->requested_size,
                                                  size - chunk->requested_size);
#endif

                chunk->requested_size = size;
                /* set mark to catch clobber of "unused" space */
                if (size < oldsize)
                        ((char *) pointer)[size] = 0x7E;
#endif
                return pointer;
        }

        if (oldsize > set->allocChunkLimit)
        {
                /*
                 * The chunk must have been allocated as a single-chunk block.  Find
                 * the containing block and use realloc() to make it bigger with
                 * minimum space wastage.
                 */
                AllocBlock      block = set->blocks;
                AllocBlock      prevblock = NULL;
                Size            chksize;
                Size            blksize;

                while (block != NULL)
                {
                        if (chunk == (AllocChunk) (((char *) block) + ALLOC_BLOCKHDRSZ))
                                break;
                        prevblock = block;
                        block = block->next;
                }
                if (block == NULL)
                        elog(ERROR, "could not find block containing chunk %p", chunk);
                /* let's just make sure chunk is the only one in the block */
                Assert(block->freeptr == ((char *) block) +
                           (chunk->size + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ));

                /* Do the realloc */
                chksize = MAXALIGN(size);
                blksize = chksize + ALLOC_BLOCKHDRSZ + ALLOC_CHUNKHDRSZ;
                block = (AllocBlock) realloc(block, blksize);
                if (block == NULL)
                {
                        MemoryContextStats(TopMemoryContext);
                        ereport(ERROR,
                                        (errcode(ERRCODE_OUT_OF_MEMORY),
                                         errmsg("out of memory"),
                                         errdetail("Failed on request of size %lu.",
                                                           (unsigned long) size)));
                }
                block->freeptr = block->endptr = ((char *) block) + blksize;

                /* Update pointers since block has likely been moved */
                chunk = (AllocChunk) (((char *) block) + ALLOC_BLOCKHDRSZ);
                if (prevblock == NULL)
                        set->blocks = block;
                else
                        prevblock->next = block;
                chunk->size = chksize;

#ifdef MEMORY_CONTEXT_CHECKING
#ifdef RANDOMIZE_ALLOCATED_MEMORY
                /* We can only fill the extra space if we know the prior request */
                randomize_mem((char *) AllocChunkGetPointer(chunk) + chunk->requested_size,
                                          size - chunk->requested_size);
#endif

                chunk->requested_size = size;
                /* set mark to catch clobber of "unused" space */
                if (size < chunk->size)
                        ((char *) AllocChunkGetPointer(chunk))[size] = 0x7E;
#endif

                return AllocChunkGetPointer(chunk);
        }
        else
        {
                /*
                 * Small-chunk case.  We just do this by brute force, ie, allocate a
                 * new chunk and copy the data.  Since we know the existing data isn't
                 * huge, this won't involve any great memcpy expense, so it's not
                 * worth being smarter.  (At one time we tried to avoid memcpy when it
                 * was possible to enlarge the chunk in-place, but that turns out to
                 * misbehave unpleasantly for repeated cycles of
                 * palloc/repalloc/pfree: the eventually freed chunks go into the
                 * wrong freelist for the next initial palloc request, and so we leak
                 * memory indefinitely.  See pgsql-hackers archives for 2007-08-11.)
                 */
                AllocPointer newPointer;

                /* allocate new chunk */
                newPointer = AllocSetAlloc((MemoryContext) set, size);

                /* transfer existing data (certain to fit) */
                memcpy(newPointer, pointer, oldsize);

                /* free old chunk */
                AllocSetFree((MemoryContext) set, pointer);

                return newPointer;
        }
}

/*
 * AllocSetGetChunkSpace
 *              Given a currently-allocated chunk, determine the total space
 *              it occupies (including all memory-allocation overhead).
 */
static Size
AllocSetGetChunkSpace(MemoryContext context, void *pointer)
{
        AllocChunk      chunk = AllocPointerGetChunk(pointer);

        return chunk->size + ALLOC_CHUNKHDRSZ;
}

/*
 * AllocSetIsEmpty
 *              Is an allocset empty of any allocated space?
 */
static bool
AllocSetIsEmpty(MemoryContext context)
{
        AllocSet        set = (AllocSet) context;

        /*
         * For now, we say "empty" only if the context is new or just reset. We
         * could examine the freelists to determine if all space has been freed,
         * but it's not really worth the trouble for present uses of this
         * functionality.
         */
        if (set->isReset)
                return true;
        return false;
}

/*
 * AllocSetStats
 *              Displays stats about memory consumption of an allocset.
 */
static void
AllocSetStats(MemoryContext context, int level)
{
        AllocSet        set = (AllocSet) context;
        long            nblocks = 0;
        long            nchunks = 0;
        long            totalspace = 0;
        long            freespace = 0;
        AllocBlock      block;
        AllocChunk      chunk;
        int                     fidx;
        int                     i;

        for (block = set->blocks; block != NULL; block = block->next)
        {
                nblocks++;
                totalspace += block->endptr - ((char *) block);
                freespace += block->endptr - block->freeptr;
        }
        for (fidx = 0; fidx < ALLOCSET_NUM_FREELISTS; fidx++)
        {
                for (chunk = set->freelist[fidx]; chunk != NULL;
                         chunk = (AllocChunk) chunk->aset)
                {
                        nchunks++;
                        freespace += chunk->size + ALLOC_CHUNKHDRSZ;
                }
        }

        for (i = 0; i < level; i++)
                fprintf(stderr, "  ");

        fprintf(stderr,
                        "%s: %lu total in %ld blocks; %lu free (%ld chunks); %lu used\n",
                        set->header.name, totalspace, nblocks, freespace, nchunks,
                        totalspace - freespace);
}


#ifdef MEMORY_CONTEXT_CHECKING

/*
 * AllocSetCheck
 *              Walk through chunks and check consistency of memory.
 *
 * NOTE: report errors as WARNING, *not* ERROR or FATAL.  Otherwise you'll
 * find yourself in an infinite loop when trouble occurs, because this
 * routine will be entered again when elog cleanup tries to release memory!
 */
static void
AllocSetCheck(MemoryContext context)
{
        AllocSet        set = (AllocSet) context;
        char       *name = set->header.name;
        AllocBlock      block;

        for (block = set->blocks; block != NULL; block = block->next)
        {
                char       *bpoz = ((char *) block) + ALLOC_BLOCKHDRSZ;
                long            blk_used = block->freeptr - bpoz;
                long            blk_data = 0;
                long            nchunks = 0;

                /*
                 * Empty block - empty can be keeper-block only
                 */
                if (!blk_used)
                {
                        if (set->keeper != block)
                                elog(WARNING, "problem in alloc set %s: empty block %p",
                                         name, block);
                }

                /*
                 * Chunk walker
                 */
                while (bpoz < block->freeptr)
                {
                        AllocChunk      chunk = (AllocChunk) bpoz;
                        Size            chsize,
                                                dsize;
                        char       *chdata_end;

                        chsize = chunk->size;           /* aligned chunk size */
                        dsize = chunk->requested_size;          /* real data */
                        chdata_end = ((char *) chunk) + (ALLOC_CHUNKHDRSZ + dsize);

                        /*
                         * Check chunk size
                         */
                        if (dsize > chsize)
                                elog(WARNING, "problem in alloc set %s: req size > alloc size for chunk %p in block %p",
                                         name, chunk, block);
                        if (chsize < (1 << ALLOC_MINBITS))
                                elog(WARNING, "problem in alloc set %s: bad size %lu for chunk %p in block %p",
                                         name, (unsigned long) chsize, chunk, block);

                        /* single-chunk block? */
                        if (chsize > set->allocChunkLimit &&
                                chsize + ALLOC_CHUNKHDRSZ != blk_used)
                                elog(WARNING, "problem in alloc set %s: bad single-chunk %p in block %p",
                                         name, chunk, block);

                        /*
                         * If chunk is allocated, check for correct aset pointer. (If it's
                         * free, the aset is the freelist pointer, which we can't check as
                         * easily...)
                         */
                        if (dsize > 0 && chunk->aset != (void *) set)
                                elog(WARNING, "problem in alloc set %s: bogus aset link in block %p, chunk %p",
                                         name, block, chunk);

                        /*
                         * Check for overwrite of "unallocated" space in chunk
                         */
                        if (dsize > 0 && dsize < chsize && *chdata_end != 0x7E)
                                elog(WARNING, "problem in alloc set %s: detected write past chunk end in block %p, chunk %p",
                                         name, block, chunk);

                        blk_data += chsize;
                        nchunks++;

                        bpoz += ALLOC_CHUNKHDRSZ + chsize;
                }

                if ((blk_data + (nchunks * ALLOC_CHUNKHDRSZ)) != blk_used)
                        elog(WARNING, "problem in alloc set %s: found inconsistent memory block %p",
                                 name, block);
        }
}

#endif   /* MEMORY_CONTEXT_CHECKING */