hashutil.c

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/*-------------------------------------------------------------------------
 *
 * hashutil.c
 *    Utility code for Postgres hash implementation.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/hash/hashutil.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/hash.h"
#include "access/reloptions.h"
#include "access/relscan.h"
#include "port/pg_bitutils.h"
#include "utils/lsyscache.h"
#include "utils/rel.h"
 
#define CALC_NEW_BUCKET(old_bucket, lowmask) \
            old_bucket | (lowmask + 1)
 
/*
 * _hash_checkqual -- does the index tuple satisfy the scan conditions?
 */
bool
_hash_checkqual(IndexScanDesc scan, IndexTuple itup)
{
    /*
     * Currently, we can't check any of the scan conditions since we do not
     * have the original index entry value to supply to the sk_func. Always
     * return true; we expect that hashgettuple already set the recheck flag
     * to make the main indexscan code do it.
     */
#ifdef NOT_USED
    TupleDesc   tupdesc = RelationGetDescr(scan->indexRelation);
    ScanKey     key = scan->keyData;
    int         scanKeySize = scan->numberOfKeys;
 
    while (scanKeySize > 0)
    {
        Datum       datum;
        bool        isNull;
        Datum       test;
 
        datum = index_getattr(itup,
                              key->sk_attno,
                              tupdesc,
                              &isNull);
 
        /* assume sk_func is strict */
        if (isNull)
            return false;
        if (key->sk_flags & SK_ISNULL)
            return false;
 
        test = FunctionCall2Coll(&key->sk_func, key->sk_collation,
                                 datum, key->sk_argument);
 
        if (!DatumGetBool(test))
            return false;
 
        key++;
        scanKeySize--;
    }
#endif
 
    return true;
}
 
/*
 * _hash_datum2hashkey -- given a Datum, call the index's hash function
 *
 * The Datum is assumed to be of the index's column type, so we can use the
 * "primary" hash function that's tracked for us by the generic index code.
 */
uint32
_hash_datum2hashkey(Relation rel, Datum key)
{
    FmgrInfo   *procinfo;
    Oid         collation;
 
    /* XXX assumes index has only one attribute */
    procinfo = index_getprocinfo(rel, 1, HASHSTANDARD_PROC);
    collation = rel->rd_indcollation[0];
 
    return DatumGetUInt32(FunctionCall1Coll(procinfo, collation, key));
}
 
/*
 * _hash_datum2hashkey_type -- given a Datum of a specified type,
 *          hash it in a fashion compatible with this index
 *
 * This is much more expensive than _hash_datum2hashkey, so use it only in
 * cross-type situations.
 */
uint32
_hash_datum2hashkey_type(Relation rel, Datum key, Oid keytype)
{
    RegProcedure hash_proc;
    Oid         collation;
 
    /* XXX assumes index has only one attribute */
    hash_proc = get_opfamily_proc(rel->rd_opfamily[0],
                                  keytype,
                                  keytype,
                                  HASHSTANDARD_PROC);
    if (!RegProcedureIsValid(hash_proc))
        elog(ERROR, "missing support function %d(%u,%u) for index \"%s\"",
             HASHSTANDARD_PROC, keytype, keytype,
             RelationGetRelationName(rel));
    collation = rel->rd_indcollation[0];
 
    return DatumGetUInt32(OidFunctionCall1Coll(hash_proc, collation, key));
}
 
/*
 * _hash_hashkey2bucket -- determine which bucket the hashkey maps to.
 */
Bucket
_hash_hashkey2bucket(uint32 hashkey, uint32 maxbucket,
                     uint32 highmask, uint32 lowmask)
{
    Bucket      bucket;
 
    bucket = hashkey & highmask;
    if (bucket > maxbucket)
        bucket = bucket & lowmask;
 
    return bucket;
}
 
/*
 * _hash_spareindex -- returns spare index / global splitpoint phase of the
 *                     bucket
 */
uint32
_hash_spareindex(uint32 num_bucket)
{
    uint32      splitpoint_group;
    uint32      splitpoint_phases;
 
    splitpoint_group = pg_ceil_log2_32(num_bucket);
 
    if (splitpoint_group < HASH_SPLITPOINT_GROUPS_WITH_ONE_PHASE)
        return splitpoint_group;
 
    /* account for single-phase groups */
    splitpoint_phases = HASH_SPLITPOINT_GROUPS_WITH_ONE_PHASE;
 
    /* account for multi-phase groups before splitpoint_group */
    splitpoint_phases +=
        ((splitpoint_group - HASH_SPLITPOINT_GROUPS_WITH_ONE_PHASE) <<
         HASH_SPLITPOINT_PHASE_BITS);
 
    /* account for phases within current group */
    splitpoint_phases +=
        (((num_bucket - 1) >>
          (splitpoint_group - (HASH_SPLITPOINT_PHASE_BITS + 1))) &
         HASH_SPLITPOINT_PHASE_MASK);   /* to 0-based value. */
 
    return splitpoint_phases;
}
 
/*
 *  _hash_get_totalbuckets -- returns total number of buckets allocated till
 *                          the given splitpoint phase.
 */
uint32
_hash_get_totalbuckets(uint32 splitpoint_phase)
{
    uint32      splitpoint_group;
    uint32      total_buckets;
    uint32      phases_within_splitpoint_group;
 
    if (splitpoint_phase < HASH_SPLITPOINT_GROUPS_WITH_ONE_PHASE)
        return (1 << splitpoint_phase);
 
    /* get splitpoint's group */
    splitpoint_group = HASH_SPLITPOINT_GROUPS_WITH_ONE_PHASE;
    splitpoint_group +=
        ((splitpoint_phase - HASH_SPLITPOINT_GROUPS_WITH_ONE_PHASE) >>
         HASH_SPLITPOINT_PHASE_BITS);
 
    /* account for buckets before splitpoint_group */
    total_buckets = (1 << (splitpoint_group - 1));
 
    /* account for buckets within splitpoint_group */
    phases_within_splitpoint_group =
        (((splitpoint_phase - HASH_SPLITPOINT_GROUPS_WITH_ONE_PHASE) &
          HASH_SPLITPOINT_PHASE_MASK) + 1); /* from 0-based to 1-based */
    total_buckets +=
        (((1 << (splitpoint_group - 1)) >> HASH_SPLITPOINT_PHASE_BITS) *
         phases_within_splitpoint_group);
 
    return total_buckets;
}
 
/*
 * _hash_checkpage -- sanity checks on the format of all hash pages
 *
 * If flags is not zero, it is a bitwise OR of the acceptable page types
 * (values of hasho_flag & LH_PAGE_TYPE).
 */
void
_hash_checkpage(Relation rel, Buffer buf, int flags)
{
    Page        page = BufferGetPage(buf);
 
    /*
     * ReadBuffer verifies that every newly-read page passes
     * PageHeaderIsValid, which means it either contains a reasonably sane
     * page header or is all-zero.  We have to defend against the all-zero
     * case, however.
     */
    if (PageIsNew(page))
        ereport(ERROR,
                (errcode(ERRCODE_INDEX_CORRUPTED),
                 errmsg("index \"%s\" contains unexpected zero page at block %u",
                        RelationGetRelationName(rel),
                        BufferGetBlockNumber(buf)),
                 errhint("Please REINDEX it.")));
 
    /*
     * Additionally check that the special area looks sane.
     */
    if (PageGetSpecialSize(page) != MAXALIGN(sizeof(HashPageOpaqueData)))
        ereport(ERROR,
                (errcode(ERRCODE_INDEX_CORRUPTED),
                 errmsg("index \"%s\" contains corrupted page at block %u",
                        RelationGetRelationName(rel),
                        BufferGetBlockNumber(buf)),
                 errhint("Please REINDEX it.")));
 
    if (flags)
    {
        HashPageOpaque opaque = HashPageGetOpaque(page);
 
        if ((opaque->hasho_flag & flags) == 0)
            ereport(ERROR,
                    (errcode(ERRCODE_INDEX_CORRUPTED),
                     errmsg("index \"%s\" contains corrupted page at block %u",
                            RelationGetRelationName(rel),
                            BufferGetBlockNumber(buf)),
                     errhint("Please REINDEX it.")));
    }
 
    /*
     * When checking the metapage, also verify magic number and version.
     */
    if (flags == LH_META_PAGE)
    {
        HashMetaPage metap = HashPageGetMeta(page);
 
        if (metap->hashm_magic != HASH_MAGIC)
            ereport(ERROR,
                    (errcode(ERRCODE_INDEX_CORRUPTED),
                     errmsg("index \"%s\" is not a hash index",
                            RelationGetRelationName(rel))));
 
        if (metap->hashm_version != HASH_VERSION)
            ereport(ERROR,
                    (errcode(ERRCODE_INDEX_CORRUPTED),
                     errmsg("index \"%s\" has wrong hash version",
                            RelationGetRelationName(rel)),
                     errhint("Please REINDEX it.")));
    }
}
 
bytea *
hashoptions(Datum reloptions, bool validate)
{
    static const relopt_parse_elt tab[] = {
        {"fillfactor", RELOPT_TYPE_INT, offsetof(HashOptions, fillfactor)},
    };
 
    return (bytea *) build_reloptions(reloptions, validate,
                                      RELOPT_KIND_HASH,
                                      sizeof(HashOptions),
                                      tab, lengthof(tab));
}
 
/*
 * _hash_get_indextuple_hashkey - get the hash index tuple's hash key value
 */
uint32
_hash_get_indextuple_hashkey(IndexTuple itup)
{
    char       *attp;
 
    /*
     * We assume the hash key is the first attribute and can't be null, so
     * this can be done crudely but very very cheaply ...
     */
    attp = (char *) itup + IndexInfoFindDataOffset(itup->t_info);
    return *((uint32 *) attp);
}
 
/*
 * _hash_convert_tuple - convert raw index data to hash key
 *
 * Inputs: values and isnull arrays for the user data column(s)
 * Outputs: values and isnull arrays for the index tuple, suitable for
 *      passing to index_form_tuple().
 *
 * Returns true if successful, false if not (because there are null values).
 * On a false result, the given data need not be indexed.
 *
 * Note: callers know that the index-column arrays are always of length 1.
 * In principle, there could be more than one input column, though we do not
 * currently support that.
 */
bool
_hash_convert_tuple(Relation index,
                    const Datum *user_values, const bool *user_isnull,
                    Datum *index_values, bool *index_isnull)
{
    uint32      hashkey;
 
    /*
     * We do not insert null values into hash indexes.  This is okay because
     * the only supported search operator is '=', and we assume it is strict.
     */
    if (user_isnull[0])
        return false;
 
    hashkey = _hash_datum2hashkey(index, user_values[0]);
    index_values[0] = UInt32GetDatum(hashkey);
    index_isnull[0] = false;
    return true;
}
 
/*
 * _hash_binsearch - Return the offset number in the page where the
 *                   specified hash value should be sought or inserted.
 *
 * We use binary search, relying on the assumption that the existing entries
 * are ordered by hash key.
 *
 * Returns the offset of the first index entry having hashkey >= hash_value,
 * or the page's max offset plus one if hash_value is greater than all
 * existing hash keys in the page.  This is the appropriate place to start
 * a search, or to insert a new item.
 */
OffsetNumber
_hash_binsearch(Page page, uint32 hash_value)
{
    OffsetNumber upper;
    OffsetNumber lower;
 
    /* Loop invariant: lower <= desired place <= upper */
    upper = PageGetMaxOffsetNumber(page) + 1;
    lower = FirstOffsetNumber;
 
    while (upper > lower)
    {
        OffsetNumber off;
        IndexTuple  itup;
        uint32      hashkey;
 
        off = (upper + lower) / 2;
        Assert(OffsetNumberIsValid(off));
 
        itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, off));
        hashkey = _hash_get_indextuple_hashkey(itup);
        if (hashkey < hash_value)
            lower = off + 1;
        else
            upper = off;
    }
 
    return lower;
}
 
/*
 * _hash_binsearch_last
 *
 * Same as above, except that if there are multiple matching items in the
 * page, we return the offset of the last one instead of the first one,
 * and the possible range of outputs is 0..maxoffset not 1..maxoffset+1.
 * This is handy for starting a new page in a backwards scan.
 */
OffsetNumber
_hash_binsearch_last(Page page, uint32 hash_value)
{
    OffsetNumber upper;
    OffsetNumber lower;
 
    /* Loop invariant: lower <= desired place <= upper */
    upper = PageGetMaxOffsetNumber(page);
    lower = FirstOffsetNumber - 1;
 
    while (upper > lower)
    {
        IndexTuple  itup;
        OffsetNumber off;
        uint32      hashkey;
 
        off = (upper + lower + 1) / 2;
        Assert(OffsetNumberIsValid(off));
 
        itup = (IndexTuple) PageGetItem(page, PageGetItemId(page, off));
        hashkey = _hash_get_indextuple_hashkey(itup);
        if (hashkey > hash_value)
            upper = off - 1;
        else
            lower = off;
    }
 
    return lower;
}
 
/*
 *  _hash_get_oldblock_from_newbucket() -- get the block number of a bucket
 *          from which current (new) bucket is being split.
 */
BlockNumber
_hash_get_oldblock_from_newbucket(Relation rel, Bucket new_bucket)
{
    Bucket      old_bucket;
    uint32      mask;
    Buffer      metabuf;
    HashMetaPage metap;
    BlockNumber blkno;
 
    /*
     * To get the old bucket from the current bucket, we need a mask to modulo
     * into lower half of table.  This mask is stored in meta page as
     * hashm_lowmask, but here we can't rely on the same, because we need a
     * value of lowmask that was prevalent at the time when bucket split was
     * started.  Masking the most significant bit of new bucket would give us
     * old bucket.
     */
    mask = (((uint32) 1) << pg_leftmost_one_pos32(new_bucket)) - 1;
    old_bucket = new_bucket & mask;
 
    metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_READ, LH_META_PAGE);
    metap = HashPageGetMeta(BufferGetPage(metabuf));
 
    blkno = BUCKET_TO_BLKNO(metap, old_bucket);
 
    _hash_relbuf(rel, metabuf);
 
    return blkno;
}
 
/*
 *  _hash_get_newblock_from_oldbucket() -- get the block number of a bucket
 *          that will be generated after split from old bucket.
 *
 * This is used to find the new bucket from old bucket based on current table
 * half.  It is mainly required to finish the incomplete splits where we are
 * sure that not more than one bucket could have split in progress from old
 * bucket.
 */
BlockNumber
_hash_get_newblock_from_oldbucket(Relation rel, Bucket old_bucket)
{
    Bucket      new_bucket;
    Buffer      metabuf;
    HashMetaPage metap;
    BlockNumber blkno;
 
    metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_READ, LH_META_PAGE);
    metap = HashPageGetMeta(BufferGetPage(metabuf));
 
    new_bucket = _hash_get_newbucket_from_oldbucket(rel, old_bucket,
                                                    metap->hashm_lowmask,
                                                    metap->hashm_maxbucket);
    blkno = BUCKET_TO_BLKNO(metap, new_bucket);
 
    _hash_relbuf(rel, metabuf);
 
    return blkno;
}
 
/*
 *  _hash_get_newbucket_from_oldbucket() -- get the new bucket that will be
 *          generated after split from current (old) bucket.
 *
 * This is used to find the new bucket from old bucket.  New bucket can be
 * obtained by OR'ing old bucket with most significant bit of current table
 * half (lowmask passed in this function can be used to identify msb of
 * current table half).  There could be multiple buckets that could have
 * been split from current bucket.  We need the first such bucket that exists.
 * Caller must ensure that no more than one split has happened from old
 * bucket.
 */
Bucket
_hash_get_newbucket_from_oldbucket(Relation rel, Bucket old_bucket,
                                   uint32 lowmask, uint32 maxbucket)
{
    Bucket      new_bucket;
 
    new_bucket = CALC_NEW_BUCKET(old_bucket, lowmask);
    if (new_bucket > maxbucket)
    {
        lowmask = lowmask >> 1;
        new_bucket = CALC_NEW_BUCKET(old_bucket, lowmask);
    }
 
    return new_bucket;
}
 
/*
 * _hash_kill_items - set LP_DEAD state for items an indexscan caller has
 * told us were killed.
 *
 * scan->opaque, referenced locally through so, contains information about the
 * current page and killed tuples thereon (generally, this should only be
 * called if so->numKilled > 0).
 *
 * The caller does not have a lock on the page and may or may not have the
 * page pinned in a buffer.  Note that read-lock is sufficient for setting
 * LP_DEAD status (which is only a hint).
 *
 * The caller must have pin on bucket buffer, but may or may not have pin
 * on overflow buffer, as indicated by HashScanPosIsPinned(so->currPos).
 *
 * We match items by heap TID before assuming they are the right ones to
 * delete.
 *
 * There are never any scans active in a bucket at the time VACUUM begins,
 * because VACUUM takes a cleanup lock on the primary bucket page and scans
 * hold a pin.  A scan can begin after VACUUM leaves the primary bucket page
 * but before it finishes the entire bucket, but it can never pass VACUUM,
 * because VACUUM always locks the next page before releasing the lock on
 * the previous one.  Therefore, we don't have to worry about accidentally
 * killing a TID that has been reused for an unrelated tuple.
 */
void
_hash_kill_items(IndexScanDesc scan)
{
    HashScanOpaque so = (HashScanOpaque) scan->opaque;
    Relation    rel = scan->indexRelation;
    BlockNumber blkno;
    Buffer      buf;
    Page        page;
    HashPageOpaque opaque;
    OffsetNumber offnum,
                maxoff;
    int         numKilled = so->numKilled;
    int         i;
    bool        killedsomething = false;
    bool        havePin = false;
 
    Assert(so->numKilled > 0);
    Assert(so->killedItems != NULL);
    Assert(HashScanPosIsValid(so->currPos));
 
    /*
     * Always reset the scan state, so we don't look for same items on other
     * pages.
     */
    so->numKilled = 0;
 
    blkno = so->currPos.currPage;
    if (HashScanPosIsPinned(so->currPos))
    {
        /*
         * We already have pin on this buffer, so, all we need to do is
         * acquire lock on it.
         */
        havePin = true;
        buf = so->currPos.buf;
        LockBuffer(buf, BUFFER_LOCK_SHARE);
    }
    else
        buf = _hash_getbuf(rel, blkno, HASH_READ, LH_OVERFLOW_PAGE);
 
    page = BufferGetPage(buf);
    opaque = HashPageGetOpaque(page);
    maxoff = PageGetMaxOffsetNumber(page);
 
    for (i = 0; i < numKilled; i++)
    {
        int         itemIndex = so->killedItems[i];
        HashScanPosItem *currItem = &so->currPos.items[itemIndex];
 
        offnum = currItem->indexOffset;
 
        Assert(itemIndex >= so->currPos.firstItem &&
               itemIndex <= so->currPos.lastItem);
 
        while (offnum <= maxoff)
        {
            ItemId      iid = PageGetItemId(page, offnum);
            IndexTuple  ituple = (IndexTuple) PageGetItem(page, iid);
 
            if (ItemPointerEquals(&ituple->t_tid, &currItem->heapTid))
            {
                /* found the item */
                ItemIdMarkDead(iid);
                killedsomething = true;
                break;          /* out of inner search loop */
            }
            offnum = OffsetNumberNext(offnum);
        }
    }
 
    /*
     * Since this can be redone later if needed, mark as dirty hint. Whenever
     * we mark anything LP_DEAD, we also set the page's
     * LH_PAGE_HAS_DEAD_TUPLES flag, which is likewise just a hint.
     */
    if (killedsomething)
    {
        opaque->hasho_flag |= LH_PAGE_HAS_DEAD_TUPLES;
        MarkBufferDirtyHint(buf, true);
    }
 
    if (so->hashso_bucket_buf == so->currPos.buf ||
        havePin)
        LockBuffer(so->currPos.buf, BUFFER_LOCK_UNLOCK);
    else
        _hash_relbuf(rel, buf);
}