execGrouping.c

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/*-------------------------------------------------------------------------
 *
 * execGrouping.c
 *    executor utility routines for grouping, hashing, and aggregation
 *
 * Note: we currently assume that equality and hashing functions are not
 * collation-sensitive, so the code in this file has no support for passing
 * collation settings through from callers.  That may have to change someday.
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/execGrouping.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "executor/executor.h"
#include "miscadmin.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"


static TupleHashTable CurTupleHashTable = NULL;

static uint32 TupleHashTableHash(const void *key, Size keysize);
static int TupleHashTableMatch(const void *key1, const void *key2,
                    Size keysize);


/*****************************************************************************
 *      Utility routines for grouping tuples together
 *****************************************************************************/

/*
 * execTuplesMatch
 *      Return true if two tuples match in all the indicated fields.
 *
 * This actually implements SQL's notion of "not distinct".  Two nulls
 * match, a null and a not-null don't match.
 *
 * slot1, slot2: the tuples to compare (must have same columns!)
 * numCols: the number of attributes to be examined
 * matchColIdx: array of attribute column numbers
 * eqFunctions: array of fmgr lookup info for the equality functions to use
 * evalContext: short-term memory context for executing the functions
 *
 * NB: evalContext is reset each time!
 */
bool
execTuplesMatch(TupleTableSlot *slot1,
                TupleTableSlot *slot2,
                int numCols,
                AttrNumber *matchColIdx,
                FmgrInfo *eqfunctions,
                MemoryContext evalContext)
{
    MemoryContext oldContext;
    bool        result;
    int         i;

    /* Reset and switch into the temp context. */
    MemoryContextReset(evalContext);
    oldContext = MemoryContextSwitchTo(evalContext);

    /*
     * We cannot report a match without checking all the fields, but we can
     * report a non-match as soon as we find unequal fields.  So, start
     * comparing at the last field (least significant sort key). That's the
     * most likely to be different if we are dealing with sorted input.
     */
    result = true;

    for (i = numCols; --i >= 0;)
    {
        AttrNumber  att = matchColIdx[i];
        Datum       attr1,
                    attr2;
        bool        isNull1,
                    isNull2;

        attr1 = slot_getattr(slot1, att, &isNull1);

        attr2 = slot_getattr(slot2, att, &isNull2);

        if (isNull1 != isNull2)
        {
            result = false;     /* one null and one not; they aren't equal */
            break;
        }

        if (isNull1)
            continue;           /* both are null, treat as equal */

        /* Apply the type-specific equality function */

        if (!DatumGetBool(FunctionCall2(&eqfunctions[i],
                                        attr1, attr2)))
        {
            result = false;     /* they aren't equal */
            break;
        }
    }

    MemoryContextSwitchTo(oldContext);

    return result;
}

/*
 * execTuplesUnequal
 *      Return true if two tuples are definitely unequal in the indicated
 *      fields.
 *
 * Nulls are neither equal nor unequal to anything else.  A true result
 * is obtained only if there are non-null fields that compare not-equal.
 *
 * Parameters are identical to execTuplesMatch.
 */
bool
execTuplesUnequal(TupleTableSlot *slot1,
                  TupleTableSlot *slot2,
                  int numCols,
                  AttrNumber *matchColIdx,
                  FmgrInfo *eqfunctions,
                  MemoryContext evalContext)
{
    MemoryContext oldContext;
    bool        result;
    int         i;

    /* Reset and switch into the temp context. */
    MemoryContextReset(evalContext);
    oldContext = MemoryContextSwitchTo(evalContext);

    /*
     * We cannot report a match without checking all the fields, but we can
     * report a non-match as soon as we find unequal fields.  So, start
     * comparing at the last field (least significant sort key). That's the
     * most likely to be different if we are dealing with sorted input.
     */
    result = false;

    for (i = numCols; --i >= 0;)
    {
        AttrNumber  att = matchColIdx[i];
        Datum       attr1,
                    attr2;
        bool        isNull1,
                    isNull2;

        attr1 = slot_getattr(slot1, att, &isNull1);

        if (isNull1)
            continue;           /* can't prove anything here */

        attr2 = slot_getattr(slot2, att, &isNull2);

        if (isNull2)
            continue;           /* can't prove anything here */

        /* Apply the type-specific equality function */

        if (!DatumGetBool(FunctionCall2(&eqfunctions[i],
                                        attr1, attr2)))
        {
            result = true;      /* they are unequal */
            break;
        }
    }

    MemoryContextSwitchTo(oldContext);

    return result;
}


/*
 * execTuplesMatchPrepare
 *      Look up the equality functions needed for execTuplesMatch or
 *      execTuplesUnequal, given an array of equality operator OIDs.
 *
 * The result is a palloc'd array.
 */
FmgrInfo *
execTuplesMatchPrepare(int numCols,
                       Oid *eqOperators)
{
    FmgrInfo   *eqFunctions = (FmgrInfo *) palloc(numCols * sizeof(FmgrInfo));
    int         i;

    for (i = 0; i < numCols; i++)
    {
        Oid         eq_opr = eqOperators[i];
        Oid         eq_function;

        eq_function = get_opcode(eq_opr);
        fmgr_info(eq_function, &eqFunctions[i]);
    }

    return eqFunctions;
}

/*
 * execTuplesHashPrepare
 *      Look up the equality and hashing functions needed for a TupleHashTable.
 *
 * This is similar to execTuplesMatchPrepare, but we also need to find the
 * hash functions associated with the equality operators.  *eqFunctions and
 * *hashFunctions receive the palloc'd result arrays.
 *
 * Note: we expect that the given operators are not cross-type comparisons.
 */
void
execTuplesHashPrepare(int numCols,
                      Oid *eqOperators,
                      FmgrInfo **eqFunctions,
                      FmgrInfo **hashFunctions)
{
    int         i;

    *eqFunctions = (FmgrInfo *) palloc(numCols * sizeof(FmgrInfo));
    *hashFunctions = (FmgrInfo *) palloc(numCols * sizeof(FmgrInfo));

    for (i = 0; i < numCols; i++)
    {
        Oid         eq_opr = eqOperators[i];
        Oid         eq_function;
        Oid         left_hash_function;
        Oid         right_hash_function;

        eq_function = get_opcode(eq_opr);
        if (!get_op_hash_functions(eq_opr,
                                   &left_hash_function, &right_hash_function))
            elog(ERROR, "could not find hash function for hash operator %u",
                 eq_opr);
        /* We're not supporting cross-type cases here */
        Assert(left_hash_function == right_hash_function);
        fmgr_info(eq_function, &(*eqFunctions)[i]);
        fmgr_info(right_hash_function, &(*hashFunctions)[i]);
    }
}


/*****************************************************************************
 *      Utility routines for all-in-memory hash tables
 *
 * These routines build hash tables for grouping tuples together (eg, for
 * hash aggregation).  There is one entry for each not-distinct set of tuples
 * presented.
 *****************************************************************************/

/*
 * Construct an empty TupleHashTable
 *
 *  numCols, keyColIdx: identify the tuple fields to use as lookup key
 *  eqfunctions: equality comparison functions to use
 *  hashfunctions: datatype-specific hashing functions to use
 *  nbuckets: initial estimate of hashtable size
 *  entrysize: size of each entry (at least sizeof(TupleHashEntryData))
 *  tablecxt: memory context in which to store table and table entries
 *  tempcxt: short-lived context for evaluation hash and comparison functions
 *
 * The function arrays may be made with execTuplesHashPrepare().  Note they
 * are not cross-type functions, but expect to see the table datatype(s)
 * on both sides.
 *
 * Note that keyColIdx, eqfunctions, and hashfunctions must be allocated in
 * storage that will live as long as the hashtable does.
 */
TupleHashTable
BuildTupleHashTable(int numCols, AttrNumber *keyColIdx,
                    FmgrInfo *eqfunctions,
                    FmgrInfo *hashfunctions,
                    long nbuckets, Size entrysize,
                    MemoryContext tablecxt, MemoryContext tempcxt)
{
    TupleHashTable hashtable;
    HASHCTL     hash_ctl;

    Assert(nbuckets > 0);
    Assert(entrysize >= sizeof(TupleHashEntryData));

    /* Limit initial table size request to not more than work_mem */
    nbuckets = Min(nbuckets, (long) ((work_mem * 1024L) / entrysize));

    hashtable = (TupleHashTable) MemoryContextAlloc(tablecxt,
                                                 sizeof(TupleHashTableData));

    hashtable->numCols = numCols;
    hashtable->keyColIdx = keyColIdx;
    hashtable->tab_hash_funcs = hashfunctions;
    hashtable->tab_eq_funcs = eqfunctions;
    hashtable->tablecxt = tablecxt;
    hashtable->tempcxt = tempcxt;
    hashtable->entrysize = entrysize;
    hashtable->tableslot = NULL;    /* will be made on first lookup */
    hashtable->inputslot = NULL;
    hashtable->in_hash_funcs = NULL;
    hashtable->cur_eq_funcs = NULL;

    MemSet(&hash_ctl, 0, sizeof(hash_ctl));
    hash_ctl.keysize = sizeof(TupleHashEntryData);
    hash_ctl.entrysize = entrysize;
    hash_ctl.hash = TupleHashTableHash;
    hash_ctl.match = TupleHashTableMatch;
    hash_ctl.hcxt = tablecxt;
    hashtable->hashtab = hash_create("TupleHashTable", nbuckets,
                                     &hash_ctl,
                    HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);

    return hashtable;
}

/*
 * Find or create a hashtable entry for the tuple group containing the
 * given tuple.  The tuple must be the same type as the hashtable entries.
 *
 * If isnew is NULL, we do not create new entries; we return NULL if no
 * match is found.
 *
 * If isnew isn't NULL, then a new entry is created if no existing entry
 * matches.  On return, *isnew is true if the entry is newly created,
 * false if it existed already.  Any extra space in a new entry has been
 * zeroed.
 */
TupleHashEntry
LookupTupleHashEntry(TupleHashTable hashtable, TupleTableSlot *slot,
                     bool *isnew)
{
    TupleHashEntry entry;
    MemoryContext oldContext;
    TupleHashTable saveCurHT;
    TupleHashEntryData dummy;
    bool        found;

    /* If first time through, clone the input slot to make table slot */
    if (hashtable->tableslot == NULL)
    {
        TupleDesc   tupdesc;

        oldContext = MemoryContextSwitchTo(hashtable->tablecxt);

        /*
         * We copy the input tuple descriptor just for safety --- we assume
         * all input tuples will have equivalent descriptors.
         */
        tupdesc = CreateTupleDescCopy(slot->tts_tupleDescriptor);
        hashtable->tableslot = MakeSingleTupleTableSlot(tupdesc);
        MemoryContextSwitchTo(oldContext);
    }

    /* Need to run the hash functions in short-lived context */
    oldContext = MemoryContextSwitchTo(hashtable->tempcxt);

    /*
     * Set up data needed by hash and match functions
     *
     * We save and restore CurTupleHashTable just in case someone manages to
     * invoke this code re-entrantly.
     */
    hashtable->inputslot = slot;
    hashtable->in_hash_funcs = hashtable->tab_hash_funcs;
    hashtable->cur_eq_funcs = hashtable->tab_eq_funcs;

    saveCurHT = CurTupleHashTable;
    CurTupleHashTable = hashtable;

    /* Search the hash table */
    dummy.firstTuple = NULL;    /* flag to reference inputslot */
    entry = (TupleHashEntry) hash_search(hashtable->hashtab,
                                         &dummy,
                                         isnew ? HASH_ENTER : HASH_FIND,
                                         &found);

    if (isnew)
    {
        if (found)
        {
            /* found pre-existing entry */
            *isnew = false;
        }
        else
        {
            /*
             * created new entry
             *
             * Zero any caller-requested space in the entry.  (This zaps the
             * "key data" dynahash.c copied into the new entry, but we don't
             * care since we're about to overwrite it anyway.)
             */
            MemSet(entry, 0, hashtable->entrysize);

            /* Copy the first tuple into the table context */
            MemoryContextSwitchTo(hashtable->tablecxt);
            entry->firstTuple = ExecCopySlotMinimalTuple(slot);

            *isnew = true;
        }
    }

    CurTupleHashTable = saveCurHT;

    MemoryContextSwitchTo(oldContext);

    return entry;
}

/*
 * Search for a hashtable entry matching the given tuple.  No entry is
 * created if there's not a match.  This is similar to the non-creating
 * case of LookupTupleHashEntry, except that it supports cross-type
 * comparisons, in which the given tuple is not of the same type as the
 * table entries.  The caller must provide the hash functions to use for
 * the input tuple, as well as the equality functions, since these may be
 * different from the table's internal functions.
 */
TupleHashEntry
FindTupleHashEntry(TupleHashTable hashtable, TupleTableSlot *slot,
                   FmgrInfo *eqfunctions,
                   FmgrInfo *hashfunctions)
{
    TupleHashEntry entry;
    MemoryContext oldContext;
    TupleHashTable saveCurHT;
    TupleHashEntryData dummy;

    /* Need to run the hash functions in short-lived context */
    oldContext = MemoryContextSwitchTo(hashtable->tempcxt);

    /*
     * Set up data needed by hash and match functions
     *
     * We save and restore CurTupleHashTable just in case someone manages to
     * invoke this code re-entrantly.
     */
    hashtable->inputslot = slot;
    hashtable->in_hash_funcs = hashfunctions;
    hashtable->cur_eq_funcs = eqfunctions;

    saveCurHT = CurTupleHashTable;
    CurTupleHashTable = hashtable;

    /* Search the hash table */
    dummy.firstTuple = NULL;    /* flag to reference inputslot */
    entry = (TupleHashEntry) hash_search(hashtable->hashtab,
                                         &dummy,
                                         HASH_FIND,
                                         NULL);

    CurTupleHashTable = saveCurHT;

    MemoryContextSwitchTo(oldContext);

    return entry;
}

/*
 * Compute the hash value for a tuple
 *
 * The passed-in key is a pointer to TupleHashEntryData.  In an actual hash
 * table entry, the firstTuple field points to a tuple (in MinimalTuple
 * format).  LookupTupleHashEntry sets up a dummy TupleHashEntryData with a
 * NULL firstTuple field --- that cues us to look at the inputslot instead.
 * This convention avoids the need to materialize virtual input tuples unless
 * they actually need to get copied into the table.
 *
 * CurTupleHashTable must be set before calling this, since dynahash.c
 * doesn't provide any API that would let us get at the hashtable otherwise.
 *
 * Also, the caller must select an appropriate memory context for running
 * the hash functions. (dynahash.c doesn't change CurrentMemoryContext.)
 */
static uint32
TupleHashTableHash(const void *key, Size keysize)
{
    MinimalTuple tuple = ((const TupleHashEntryData *) key)->firstTuple;
    TupleTableSlot *slot;
    TupleHashTable hashtable = CurTupleHashTable;
    int         numCols = hashtable->numCols;
    AttrNumber *keyColIdx = hashtable->keyColIdx;
    FmgrInfo   *hashfunctions;
    uint32      hashkey = 0;
    int         i;

    if (tuple == NULL)
    {
        /* Process the current input tuple for the table */
        slot = hashtable->inputslot;
        hashfunctions = hashtable->in_hash_funcs;
    }
    else
    {
        /* Process a tuple already stored in the table */
        /* (this case never actually occurs in current dynahash.c code) */
        slot = hashtable->tableslot;
        ExecStoreMinimalTuple(tuple, slot, false);
        hashfunctions = hashtable->tab_hash_funcs;
    }

    for (i = 0; i < numCols; i++)
    {
        AttrNumber  att = keyColIdx[i];
        Datum       attr;
        bool        isNull;

        /* rotate hashkey left 1 bit at each step */
        hashkey = (hashkey << 1) | ((hashkey & 0x80000000) ? 1 : 0);

        attr = slot_getattr(slot, att, &isNull);

        if (!isNull)            /* treat nulls as having hash key 0 */
        {
            uint32      hkey;

            hkey = DatumGetUInt32(FunctionCall1(&hashfunctions[i],
                                                attr));
            hashkey ^= hkey;
        }
    }

    return hashkey;
}

/*
 * See whether two tuples (presumably of the same hash value) match
 *
 * As above, the passed pointers are pointers to TupleHashEntryData.
 *
 * CurTupleHashTable must be set before calling this, since dynahash.c
 * doesn't provide any API that would let us get at the hashtable otherwise.
 *
 * Also, the caller must select an appropriate memory context for running
 * the compare functions.  (dynahash.c doesn't change CurrentMemoryContext.)
 */
static int
TupleHashTableMatch(const void *key1, const void *key2, Size keysize)
{
    MinimalTuple tuple1 = ((const TupleHashEntryData *) key1)->firstTuple;

#ifdef USE_ASSERT_CHECKING
    MinimalTuple tuple2 = ((const TupleHashEntryData *) key2)->firstTuple;
#endif
    TupleTableSlot *slot1;
    TupleTableSlot *slot2;
    TupleHashTable hashtable = CurTupleHashTable;

    /*
     * We assume that dynahash.c will only ever call us with the first
     * argument being an actual table entry, and the second argument being
     * LookupTupleHashEntry's dummy TupleHashEntryData.  The other direction
     * could be supported too, but is not currently used by dynahash.c.
     */
    Assert(tuple1 != NULL);
    slot1 = hashtable->tableslot;
    ExecStoreMinimalTuple(tuple1, slot1, false);
    Assert(tuple2 == NULL);
    slot2 = hashtable->inputslot;

    /* For crosstype comparisons, the inputslot must be first */
    if (execTuplesMatch(slot2,
                        slot1,
                        hashtable->numCols,
                        hashtable->keyColIdx,
                        hashtable->cur_eq_funcs,
                        hashtable->tempcxt))
        return 0;
    else
        return 1;
}