spgtextproc.c

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/*-------------------------------------------------------------------------
 *
 * spgtextproc.c
 *    implementation of radix tree (compressed trie) over text
 *
 * In a text_ops SPGiST index, inner tuples can have a prefix which is the
 * common prefix of all strings indexed under that tuple.  The node labels
 * represent the next byte of the string(s) after the prefix.  Assuming we
 * always use the longest possible prefix, we will get more than one node
 * label unless the prefix length is restricted by SPGIST_MAX_PREFIX_LENGTH.
 *
 * To reconstruct the indexed string for any index entry, concatenate the
 * inner-tuple prefixes and node labels starting at the root and working
 * down to the leaf entry, then append the datum in the leaf entry.
 * (While descending the tree, "level" is the number of bytes reconstructed
 * so far.)
 *
 * However, there are two special cases for node labels: -1 indicates that
 * there are no more bytes after the prefix-so-far, and -2 indicates that we
 * had to split an existing allTheSame tuple (in such a case we have to create
 * a node label that doesn't correspond to any string byte).  In either case,
 * the node label does not contribute anything to the reconstructed string.
 *
 * Previously, we used a node label of zero for both special cases, but
 * this was problematic because one can't tell whether a string ending at
 * the current level can be pushed down into such a child node.  For
 * backwards compatibility, we still support such node labels for reading;
 * but no new entries will ever be pushed down into a zero-labeled child.
 * No new entries ever get pushed into a -2-labeled child, either.
 *
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *          src/backend/access/spgist/spgtextproc.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/spgist.h"
#include "catalog/pg_type.h"
#include "mb/pg_wchar.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/pg_locale.h"
#include "utils/varlena.h"


/*
 * In the worst case, an inner tuple in a text radix tree could have as many
 * as 258 nodes (one for each possible byte value, plus the two special
 * cases).  Each node can take 16 bytes on MAXALIGN=8 machines.  The inner
 * tuple must fit on an index page of size BLCKSZ.  Rather than assuming we
 * know the exact amount of overhead imposed by page headers, tuple headers,
 * etc, we leave 100 bytes for that (the actual overhead should be no more
 * than 56 bytes at this writing, so there is slop in this number).
 * So we can safely create prefixes up to BLCKSZ - 258 * 16 - 100 bytes long.
 * Unfortunately, because 258 * 16 is over 4K, there is no safe prefix length
 * when BLCKSZ is less than 8K; it is always possible to get "SPGiST inner
 * tuple size exceeds maximum" if there are too many distinct next-byte values
 * at a given place in the tree.  Since use of nonstandard block sizes appears
 * to be negligible in the field, we just live with that fact for now,
 * choosing a max prefix size of 32 bytes when BLCKSZ is configured smaller
 * than default.
 */
#define SPGIST_MAX_PREFIX_LENGTH    Max((int) (BLCKSZ - 258 * 16 - 100), 32)

/*
 * Strategy for collation aware operator on text is equal to btree strategy
 * plus value of 10.
 *
 * Current collation aware strategies and their corresponding btree strategies:
 * 11 BTLessStrategyNumber
 * 12 BTLessEqualStrategyNumber
 * 14 BTGreaterEqualStrategyNumber
 * 15 BTGreaterStrategyNumber
 */
#define SPG_STRATEGY_ADDITION   (10)
#define SPG_IS_COLLATION_AWARE_STRATEGY(s) ((s) > SPG_STRATEGY_ADDITION \
                                         && (s) != RTPrefixStrategyNumber)

/* Struct for sorting values in picksplit */
typedef struct spgNodePtr
{
    Datum       d;
    int         i;
    int16       c;
} spgNodePtr;


Datum
spg_text_config(PG_FUNCTION_ARGS)
{
    /* spgConfigIn *cfgin = (spgConfigIn *) PG_GETARG_POINTER(0); */
    spgConfigOut *cfg = (spgConfigOut *) PG_GETARG_POINTER(1);

    cfg->prefixType = TEXTOID;
    cfg->labelType = INT2OID;
    cfg->canReturnData = true;
    cfg->longValuesOK = true;   /* suffixing will shorten long values */
    PG_RETURN_VOID();
}

/*
 * Form a text datum from the given not-necessarily-null-terminated string,
 * using short varlena header format if possible
 */
static Datum
formTextDatum(const char *data, int datalen)
{
    char       *p;

    p = (char *) palloc(datalen + VARHDRSZ);

    if (datalen + VARHDRSZ_SHORT <= VARATT_SHORT_MAX)
    {
        SET_VARSIZE_SHORT(p, datalen + VARHDRSZ_SHORT);
        if (datalen)
            memcpy(p + VARHDRSZ_SHORT, data, datalen);
    }
    else
    {
        SET_VARSIZE(p, datalen + VARHDRSZ);
        memcpy(p + VARHDRSZ, data, datalen);
    }

    return PointerGetDatum(p);
}

/*
 * Find the length of the common prefix of a and b
 */
static int
commonPrefix(const char *a, const char *b, int lena, int lenb)
{
    int         i = 0;

    while (i < lena && i < lenb && *a == *b)
    {
        a++;
        b++;
        i++;
    }

    return i;
}

/*
 * Binary search an array of int16 datums for a match to c
 *
 * On success, *i gets the match location; on failure, it gets where to insert
 */
static bool
searchChar(Datum *nodeLabels, int nNodes, int16 c, int *i)
{
    int         StopLow = 0,
                StopHigh = nNodes;

    while (StopLow < StopHigh)
    {
        int         StopMiddle = (StopLow + StopHigh) >> 1;
        int16       middle = DatumGetInt16(nodeLabels[StopMiddle]);

        if (c < middle)
            StopHigh = StopMiddle;
        else if (c > middle)
            StopLow = StopMiddle + 1;
        else
        {
            *i = StopMiddle;
            return true;
        }
    }

    *i = StopHigh;
    return false;
}

Datum
spg_text_choose(PG_FUNCTION_ARGS)
{
    spgChooseIn *in = (spgChooseIn *) PG_GETARG_POINTER(0);
    spgChooseOut *out = (spgChooseOut *) PG_GETARG_POINTER(1);
    text       *inText = DatumGetTextPP(in->datum);
    char       *inStr = VARDATA_ANY(inText);
    int         inSize = VARSIZE_ANY_EXHDR(inText);
    char       *prefixStr = NULL;
    int         prefixSize = 0;
    int         commonLen = 0;
    int16       nodeChar = 0;
    int         i = 0;

    /* Check for prefix match, set nodeChar to first byte after prefix */
    if (in->hasPrefix)
    {
        text       *prefixText = DatumGetTextPP(in->prefixDatum);

        prefixStr = VARDATA_ANY(prefixText);
        prefixSize = VARSIZE_ANY_EXHDR(prefixText);

        commonLen = commonPrefix(inStr + in->level,
                                 prefixStr,
                                 inSize - in->level,
                                 prefixSize);

        if (commonLen == prefixSize)
        {
            if (inSize - in->level > commonLen)
                nodeChar = *(unsigned char *) (inStr + in->level + commonLen);
            else
                nodeChar = -1;
        }
        else
        {
            /* Must split tuple because incoming value doesn't match prefix */
            out->resultType = spgSplitTuple;

            if (commonLen == 0)
            {
                out->result.splitTuple.prefixHasPrefix = false;
            }
            else
            {
                out->result.splitTuple.prefixHasPrefix = true;
                out->result.splitTuple.prefixPrefixDatum =
                    formTextDatum(prefixStr, commonLen);
            }
            out->result.splitTuple.prefixNNodes = 1;
            out->result.splitTuple.prefixNodeLabels =
                (Datum *) palloc(sizeof(Datum));
            out->result.splitTuple.prefixNodeLabels[0] =
                Int16GetDatum(*(unsigned char *) (prefixStr + commonLen));

            out->result.splitTuple.childNodeN = 0;

            if (prefixSize - commonLen == 1)
            {
                out->result.splitTuple.postfixHasPrefix = false;
            }
            else
            {
                out->result.splitTuple.postfixHasPrefix = true;
                out->result.splitTuple.postfixPrefixDatum =
                    formTextDatum(prefixStr + commonLen + 1,
                                  prefixSize - commonLen - 1);
            }

            PG_RETURN_VOID();
        }
    }
    else if (inSize > in->level)
    {
        nodeChar = *(unsigned char *) (inStr + in->level);
    }
    else
    {
        nodeChar = -1;
    }

    /* Look up nodeChar in the node label array */
    if (searchChar(in->nodeLabels, in->nNodes, nodeChar, &i))
    {
        /*
         * Descend to existing node.  (If in->allTheSame, the core code will
         * ignore our nodeN specification here, but that's OK.  We still have
         * to provide the correct levelAdd and restDatum values, and those are
         * the same regardless of which node gets chosen by core.)
         */
        int         levelAdd;

        out->resultType = spgMatchNode;
        out->result.matchNode.nodeN = i;
        levelAdd = commonLen;
        if (nodeChar >= 0)
            levelAdd++;
        out->result.matchNode.levelAdd = levelAdd;
        if (inSize - in->level - levelAdd > 0)
            out->result.matchNode.restDatum =
                formTextDatum(inStr + in->level + levelAdd,
                              inSize - in->level - levelAdd);
        else
            out->result.matchNode.restDatum =
                formTextDatum(NULL, 0);
    }
    else if (in->allTheSame)
    {
        /*
         * Can't use AddNode action, so split the tuple.  The upper tuple has
         * the same prefix as before and uses a dummy node label -2 for the
         * lower tuple.  The lower tuple has no prefix and the same node
         * labels as the original tuple.
         *
         * Note: it might seem tempting to shorten the upper tuple's prefix,
         * if it has one, then use its last byte as label for the lower tuple.
         * But that doesn't win since we know the incoming value matches the
         * whole prefix: we'd just end up splitting the lower tuple again.
         */
        out->resultType = spgSplitTuple;
        out->result.splitTuple.prefixHasPrefix = in->hasPrefix;
        out->result.splitTuple.prefixPrefixDatum = in->prefixDatum;
        out->result.splitTuple.prefixNNodes = 1;
        out->result.splitTuple.prefixNodeLabels = (Datum *) palloc(sizeof(Datum));
        out->result.splitTuple.prefixNodeLabels[0] = Int16GetDatum(-2);
        out->result.splitTuple.childNodeN = 0;
        out->result.splitTuple.postfixHasPrefix = false;
    }
    else
    {
        /* Add a node for the not-previously-seen nodeChar value */
        out->resultType = spgAddNode;
        out->result.addNode.nodeLabel = Int16GetDatum(nodeChar);
        out->result.addNode.nodeN = i;
    }

    PG_RETURN_VOID();
}

/* qsort comparator to sort spgNodePtr structs by "c" */
static int
cmpNodePtr(const void *a, const void *b)
{
    const spgNodePtr *aa = (const spgNodePtr *) a;
    const spgNodePtr *bb = (const spgNodePtr *) b;

    return aa->c - bb->c;
}

Datum
spg_text_picksplit(PG_FUNCTION_ARGS)
{
    spgPickSplitIn *in = (spgPickSplitIn *) PG_GETARG_POINTER(0);
    spgPickSplitOut *out = (spgPickSplitOut *) PG_GETARG_POINTER(1);
    text       *text0 = DatumGetTextPP(in->datums[0]);
    int         i,
                commonLen;
    spgNodePtr *nodes;

    /* Identify longest common prefix, if any */
    commonLen = VARSIZE_ANY_EXHDR(text0);
    for (i = 1; i < in->nTuples && commonLen > 0; i++)
    {
        text       *texti = DatumGetTextPP(in->datums[i]);
        int         tmp = commonPrefix(VARDATA_ANY(text0),
                                       VARDATA_ANY(texti),
                                       VARSIZE_ANY_EXHDR(text0),
                                       VARSIZE_ANY_EXHDR(texti));

        if (tmp < commonLen)
            commonLen = tmp;
    }

    /*
     * Limit the prefix length, if necessary, to ensure that the resulting
     * inner tuple will fit on a page.
     */
    commonLen = Min(commonLen, SPGIST_MAX_PREFIX_LENGTH);

    /* Set node prefix to be that string, if it's not empty */
    if (commonLen == 0)
    {
        out->hasPrefix = false;
    }
    else
    {
        out->hasPrefix = true;
        out->prefixDatum = formTextDatum(VARDATA_ANY(text0), commonLen);
    }

    /* Extract the node label (first non-common byte) from each value */
    nodes = (spgNodePtr *) palloc(sizeof(spgNodePtr) * in->nTuples);

    for (i = 0; i < in->nTuples; i++)
    {
        text       *texti = DatumGetTextPP(in->datums[i]);

        if (commonLen < VARSIZE_ANY_EXHDR(texti))
            nodes[i].c = *(unsigned char *) (VARDATA_ANY(texti) + commonLen);
        else
            nodes[i].c = -1;    /* use -1 if string is all common */
        nodes[i].i = i;
        nodes[i].d = in->datums[i];
    }

    /*
     * Sort by label values so that we can group the values into nodes.  This
     * also ensures that the nodes are ordered by label value, allowing the
     * use of binary search in searchChar.
     */
    qsort(nodes, in->nTuples, sizeof(*nodes), cmpNodePtr);

    /* And emit results */
    out->nNodes = 0;
    out->nodeLabels = (Datum *) palloc(sizeof(Datum) * in->nTuples);
    out->mapTuplesToNodes = (int *) palloc(sizeof(int) * in->nTuples);
    out->leafTupleDatums = (Datum *) palloc(sizeof(Datum) * in->nTuples);

    for (i = 0; i < in->nTuples; i++)
    {
        text       *texti = DatumGetTextPP(nodes[i].d);
        Datum       leafD;

        if (i == 0 || nodes[i].c != nodes[i - 1].c)
        {
            out->nodeLabels[out->nNodes] = Int16GetDatum(nodes[i].c);
            out->nNodes++;
        }

        if (commonLen < VARSIZE_ANY_EXHDR(texti))
            leafD = formTextDatum(VARDATA_ANY(texti) + commonLen + 1,
                                  VARSIZE_ANY_EXHDR(texti) - commonLen - 1);
        else
            leafD = formTextDatum(NULL, 0);

        out->leafTupleDatums[nodes[i].i] = leafD;
        out->mapTuplesToNodes[nodes[i].i] = out->nNodes - 1;
    }

    PG_RETURN_VOID();
}

Datum
spg_text_inner_consistent(PG_FUNCTION_ARGS)
{
    spgInnerConsistentIn *in = (spgInnerConsistentIn *) PG_GETARG_POINTER(0);
    spgInnerConsistentOut *out = (spgInnerConsistentOut *) PG_GETARG_POINTER(1);
    bool        collate_is_c = lc_collate_is_c(PG_GET_COLLATION());
    text       *reconstructedValue;
    text       *reconstrText;
    int         maxReconstrLen;
    text       *prefixText = NULL;
    int         prefixSize = 0;
    int         i;

    /*
     * Reconstruct values represented at this tuple, including parent data,
     * prefix of this tuple if any, and the node label if it's non-dummy.
     * in->level should be the length of the previously reconstructed value,
     * and the number of bytes added here is prefixSize or prefixSize + 1.
     *
     * Note: we assume that in->reconstructedValue isn't toasted and doesn't
     * have a short varlena header.  This is okay because it must have been
     * created by a previous invocation of this routine, and we always emit
     * long-format reconstructed values.
     */
    reconstructedValue = (text *) DatumGetPointer(in->reconstructedValue);
    Assert(reconstructedValue == NULL ? in->level == 0 :
           VARSIZE_ANY_EXHDR(reconstructedValue) == in->level);

    maxReconstrLen = in->level + 1;
    if (in->hasPrefix)
    {
        prefixText = DatumGetTextPP(in->prefixDatum);
        prefixSize = VARSIZE_ANY_EXHDR(prefixText);
        maxReconstrLen += prefixSize;
    }

    reconstrText = palloc(VARHDRSZ + maxReconstrLen);
    SET_VARSIZE(reconstrText, VARHDRSZ + maxReconstrLen);

    if (in->level)
        memcpy(VARDATA(reconstrText),
               VARDATA(reconstructedValue),
               in->level);
    if (prefixSize)
        memcpy(((char *) VARDATA(reconstrText)) + in->level,
               VARDATA_ANY(prefixText),
               prefixSize);
    /* last byte of reconstrText will be filled in below */

    /*
     * Scan the child nodes.  For each one, complete the reconstructed value
     * and see if it's consistent with the query.  If so, emit an entry into
     * the output arrays.
     */
    out->nodeNumbers = (int *) palloc(sizeof(int) * in->nNodes);
    out->levelAdds = (int *) palloc(sizeof(int) * in->nNodes);
    out->reconstructedValues = (Datum *) palloc(sizeof(Datum) * in->nNodes);
    out->nNodes = 0;

    for (i = 0; i < in->nNodes; i++)
    {
        int16       nodeChar = DatumGetInt16(in->nodeLabels[i]);
        int         thisLen;
        bool        res = true;
        int         j;

        /* If nodeChar is a dummy value, don't include it in data */
        if (nodeChar <= 0)
            thisLen = maxReconstrLen - 1;
        else
        {
            ((unsigned char *) VARDATA(reconstrText))[maxReconstrLen - 1] = nodeChar;
            thisLen = maxReconstrLen;
        }

        for (j = 0; j < in->nkeys; j++)
        {
            StrategyNumber strategy = in->scankeys[j].sk_strategy;
            text       *inText;
            int         inSize;
            int         r;

            /*
             * If it's a collation-aware operator, but the collation is C, we
             * can treat it as non-collation-aware.  With non-C collation we
             * need to traverse whole tree :-( so there's no point in making
             * any check here.  (Note also that our reconstructed value may
             * well end with a partial multibyte character, so that applying
             * any encoding-sensitive test to it would be risky anyhow.)
             */
            if (SPG_IS_COLLATION_AWARE_STRATEGY(strategy))
            {
                if (collate_is_c)
                    strategy -= SPG_STRATEGY_ADDITION;
                else
                    continue;
            }

            inText = DatumGetTextPP(in->scankeys[j].sk_argument);
            inSize = VARSIZE_ANY_EXHDR(inText);

            r = memcmp(VARDATA(reconstrText), VARDATA_ANY(inText),
                       Min(inSize, thisLen));

            switch (strategy)
            {
                case BTLessStrategyNumber:
                case BTLessEqualStrategyNumber:
                    if (r > 0)
                        res = false;
                    break;
                case BTEqualStrategyNumber:
                    if (r != 0 || inSize < thisLen)
                        res = false;
                    break;
                case BTGreaterEqualStrategyNumber:
                case BTGreaterStrategyNumber:
                    if (r < 0)
                        res = false;
                    break;
                case RTPrefixStrategyNumber:
                    if (r != 0)
                        res = false;
                    break;
                default:
                    elog(ERROR, "unrecognized strategy number: %d",
                         in->scankeys[j].sk_strategy);
                    break;
            }

            if (!res)
                break;          /* no need to consider remaining conditions */
        }

        if (res)
        {
            out->nodeNumbers[out->nNodes] = i;
            out->levelAdds[out->nNodes] = thisLen - in->level;
            SET_VARSIZE(reconstrText, VARHDRSZ + thisLen);
            out->reconstructedValues[out->nNodes] =
                datumCopy(PointerGetDatum(reconstrText), false, -1);
            out->nNodes++;
        }
    }

    PG_RETURN_VOID();
}

Datum
spg_text_leaf_consistent(PG_FUNCTION_ARGS)
{
    spgLeafConsistentIn *in = (spgLeafConsistentIn *) PG_GETARG_POINTER(0);
    spgLeafConsistentOut *out = (spgLeafConsistentOut *) PG_GETARG_POINTER(1);
    int         level = in->level;
    text       *leafValue,
               *reconstrValue = NULL;
    char       *fullValue;
    int         fullLen;
    bool        res;
    int         j;

    /* all tests are exact */
    out->recheck = false;

    leafValue = DatumGetTextPP(in->leafDatum);

    /* As above, in->reconstructedValue isn't toasted or short. */
    if (DatumGetPointer(in->reconstructedValue))
        reconstrValue = (text *) DatumGetPointer(in->reconstructedValue);

    Assert(reconstrValue == NULL ? level == 0 :
           VARSIZE_ANY_EXHDR(reconstrValue) == level);

    /* Reconstruct the full string represented by this leaf tuple */
    fullLen = level + VARSIZE_ANY_EXHDR(leafValue);
    if (VARSIZE_ANY_EXHDR(leafValue) == 0 && level > 0)
    {
        fullValue = VARDATA(reconstrValue);
        out->leafValue = PointerGetDatum(reconstrValue);
    }
    else
    {
        text       *fullText = palloc(VARHDRSZ + fullLen);

        SET_VARSIZE(fullText, VARHDRSZ + fullLen);
        fullValue = VARDATA(fullText);
        if (level)
            memcpy(fullValue, VARDATA(reconstrValue), level);
        if (VARSIZE_ANY_EXHDR(leafValue) > 0)
            memcpy(fullValue + level, VARDATA_ANY(leafValue),
                   VARSIZE_ANY_EXHDR(leafValue));
        out->leafValue = PointerGetDatum(fullText);
    }

    /* Perform the required comparison(s) */
    res = true;
    for (j = 0; j < in->nkeys; j++)
    {
        StrategyNumber strategy = in->scankeys[j].sk_strategy;
        text       *query = DatumGetTextPP(in->scankeys[j].sk_argument);
        int         queryLen = VARSIZE_ANY_EXHDR(query);
        int         r;

        if (strategy == RTPrefixStrategyNumber)
        {
            /*
             * if level >= length of query then reconstrValue must begin with
             * query (prefix) string, so we don't need to check it again.
             */
            res = (level >= queryLen) ||
                DatumGetBool(DirectFunctionCall2Coll(text_starts_with,
                                                     PG_GET_COLLATION(),
                                                     out->leafValue,
                                                     PointerGetDatum(query)));

            if (!res)           /* no need to consider remaining conditions */
                break;

            continue;
        }

        if (SPG_IS_COLLATION_AWARE_STRATEGY(strategy))
        {
            /* Collation-aware comparison */
            strategy -= SPG_STRATEGY_ADDITION;

            /* If asserts enabled, verify encoding of reconstructed string */
            Assert(pg_verifymbstr(fullValue, fullLen, false));

            r = varstr_cmp(fullValue, fullLen,
                           VARDATA_ANY(query), queryLen,
                           PG_GET_COLLATION());
        }
        else
        {
            /* Non-collation-aware comparison */
            r = memcmp(fullValue, VARDATA_ANY(query), Min(queryLen, fullLen));

            if (r == 0)
            {
                if (queryLen > fullLen)
                    r = -1;
                else if (queryLen < fullLen)
                    r = 1;
            }
        }

        switch (strategy)
        {
            case BTLessStrategyNumber:
                res = (r < 0);
                break;
            case BTLessEqualStrategyNumber:
                res = (r <= 0);
                break;
            case BTEqualStrategyNumber:
                res = (r == 0);
                break;
            case BTGreaterEqualStrategyNumber:
                res = (r >= 0);
                break;
            case BTGreaterStrategyNumber:
                res = (r > 0);
                break;
            default:
                elog(ERROR, "unrecognized strategy number: %d",
                     in->scankeys[j].sk_strategy);
                res = false;
                break;
        }

        if (!res)
            break;              /* no need to consider remaining conditions */
    }

    PG_RETURN_BOOL(res);
}