partcache.c

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/*-------------------------------------------------------------------------
 *
 * partcache.c
 *      Support routines for manipulating partition information cached in
 *      relcache
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *        src/backend/utils/cache/partcache.c
 *
 *-------------------------------------------------------------------------
*/
#include "postgres.h"

#include "access/hash.h"
#include "access/htup_details.h"
#include "access/nbtree.h"
#include "access/relation.h"
#include "catalog/partition.h"
#include "catalog/pg_inherits.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_partitioned_table.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/optimizer.h"
#include "partitioning/partbounds.h"
#include "rewrite/rewriteHandler.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/partcache.h"
#include "utils/rel.h"
#include "utils/syscache.h"


static void RelationBuildPartitionKey(Relation relation);
static List *generate_partition_qual(Relation rel);

/*
 * RelationGetPartitionKey -- get partition key, if relation is partitioned
 *
 * Note: partition keys are not allowed to change after the partitioned rel
 * is created.  RelationClearRelation knows this and preserves rd_partkey
 * across relcache rebuilds, as long as the relation is open.  Therefore,
 * even though we hand back a direct pointer into the relcache entry, it's
 * safe for callers to continue to use that pointer as long as they hold
 * the relation open.
 */
PartitionKey
RelationGetPartitionKey(Relation rel)
{
    if (rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE)
        return NULL;

    if (unlikely(rel->rd_partkey == NULL))
        RelationBuildPartitionKey(rel);

    return rel->rd_partkey;
}

/*
 * RelationBuildPartitionKey
 *      Build partition key data of relation, and attach to relcache
 *
 * Partitioning key data is a complex structure; to avoid complicated logic to
 * free individual elements whenever the relcache entry is flushed, we give it
 * its own memory context, a child of CacheMemoryContext, which can easily be
 * deleted on its own.  To avoid leaking memory in that context in case of an
 * error partway through this function, the context is initially created as a
 * child of CurTransactionContext and only re-parented to CacheMemoryContext
 * at the end, when no further errors are possible.  Also, we don't make this
 * context the current context except in very brief code sections, out of fear
 * that some of our callees allocate memory on their own which would be leaked
 * permanently.
 */
static void
RelationBuildPartitionKey(Relation relation)
{
    Form_pg_partitioned_table form;
    HeapTuple   tuple;
    bool        isnull;
    int         i;
    PartitionKey key;
    AttrNumber *attrs;
    oidvector  *opclass;
    oidvector  *collation;
    ListCell   *partexprs_item;
    Datum       datum;
    MemoryContext partkeycxt,
                oldcxt;
    int16       procnum;

    tuple = SearchSysCache1(PARTRELID,
                            ObjectIdGetDatum(RelationGetRelid(relation)));

    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for partition key of relation %u",
             RelationGetRelid(relation));

    partkeycxt = AllocSetContextCreate(CurTransactionContext,
                                       "partition key",
                                       ALLOCSET_SMALL_SIZES);
    MemoryContextCopyAndSetIdentifier(partkeycxt,
                                      RelationGetRelationName(relation));

    key = (PartitionKey) MemoryContextAllocZero(partkeycxt,
                                                sizeof(PartitionKeyData));

    /* Fixed-length attributes */
    form = (Form_pg_partitioned_table) GETSTRUCT(tuple);
    key->strategy = form->partstrat;
    key->partnatts = form->partnatts;

    /*
     * We can rely on the first variable-length attribute being mapped to the
     * relevant field of the catalog's C struct, because all previous
     * attributes are non-nullable and fixed-length.
     */
    attrs = form->partattrs.values;

    /* But use the hard way to retrieve further variable-length attributes */
    /* Operator class */
    datum = SysCacheGetAttr(PARTRELID, tuple,
                            Anum_pg_partitioned_table_partclass, &isnull);
    Assert(!isnull);
    opclass = (oidvector *) DatumGetPointer(datum);

    /* Collation */
    datum = SysCacheGetAttr(PARTRELID, tuple,
                            Anum_pg_partitioned_table_partcollation, &isnull);
    Assert(!isnull);
    collation = (oidvector *) DatumGetPointer(datum);

    /* Expressions */
    datum = SysCacheGetAttr(PARTRELID, tuple,
                            Anum_pg_partitioned_table_partexprs, &isnull);
    if (!isnull)
    {
        char       *exprString;
        Node       *expr;

        exprString = TextDatumGetCString(datum);
        expr = stringToNode(exprString);
        pfree(exprString);

        /*
         * Run the expressions through const-simplification since the planner
         * will be comparing them to similarly-processed qual clause operands,
         * and may fail to detect valid matches without this step; fix
         * opfuncids while at it.  We don't need to bother with
         * canonicalize_qual() though, because partition expressions should be
         * in canonical form already (ie, no need for OR-merging or constant
         * elimination).
         */
        expr = eval_const_expressions(NULL, expr);
        fix_opfuncids(expr);

        oldcxt = MemoryContextSwitchTo(partkeycxt);
        key->partexprs = (List *) copyObject(expr);
        MemoryContextSwitchTo(oldcxt);
    }

    /* Allocate assorted arrays in the partkeycxt, which we'll fill below */
    oldcxt = MemoryContextSwitchTo(partkeycxt);
    key->partattrs = (AttrNumber *) palloc0(key->partnatts * sizeof(AttrNumber));
    key->partopfamily = (Oid *) palloc0(key->partnatts * sizeof(Oid));
    key->partopcintype = (Oid *) palloc0(key->partnatts * sizeof(Oid));
    key->partsupfunc = (FmgrInfo *) palloc0(key->partnatts * sizeof(FmgrInfo));

    key->partcollation = (Oid *) palloc0(key->partnatts * sizeof(Oid));
    key->parttypid = (Oid *) palloc0(key->partnatts * sizeof(Oid));
    key->parttypmod = (int32 *) palloc0(key->partnatts * sizeof(int32));
    key->parttyplen = (int16 *) palloc0(key->partnatts * sizeof(int16));
    key->parttypbyval = (bool *) palloc0(key->partnatts * sizeof(bool));
    key->parttypalign = (char *) palloc0(key->partnatts * sizeof(char));
    key->parttypcoll = (Oid *) palloc0(key->partnatts * sizeof(Oid));
    MemoryContextSwitchTo(oldcxt);

    /* determine support function number to search for */
    procnum = (key->strategy == PARTITION_STRATEGY_HASH) ?
        HASHEXTENDED_PROC : BTORDER_PROC;

    /* Copy partattrs and fill other per-attribute info */
    memcpy(key->partattrs, attrs, key->partnatts * sizeof(int16));
    partexprs_item = list_head(key->partexprs);
    for (i = 0; i < key->partnatts; i++)
    {
        AttrNumber  attno = key->partattrs[i];
        HeapTuple   opclasstup;
        Form_pg_opclass opclassform;
        Oid         funcid;

        /* Collect opfamily information */
        opclasstup = SearchSysCache1(CLAOID,
                                     ObjectIdGetDatum(opclass->values[i]));
        if (!HeapTupleIsValid(opclasstup))
            elog(ERROR, "cache lookup failed for opclass %u", opclass->values[i]);

        opclassform = (Form_pg_opclass) GETSTRUCT(opclasstup);
        key->partopfamily[i] = opclassform->opcfamily;
        key->partopcintype[i] = opclassform->opcintype;

        /* Get a support function for the specified opfamily and datatypes */
        funcid = get_opfamily_proc(opclassform->opcfamily,
                                   opclassform->opcintype,
                                   opclassform->opcintype,
                                   procnum);
        if (!OidIsValid(funcid))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                     errmsg("operator class \"%s\" of access method %s is missing support function %d for type %s",
                            NameStr(opclassform->opcname),
                            (key->strategy == PARTITION_STRATEGY_HASH) ?
                            "hash" : "btree",
                            procnum,
                            format_type_be(opclassform->opcintype))));

        fmgr_info_cxt(funcid, &key->partsupfunc[i], partkeycxt);

        /* Collation */
        key->partcollation[i] = collation->values[i];

        /* Collect type information */
        if (attno != 0)
        {
            Form_pg_attribute att = TupleDescAttr(relation->rd_att, attno - 1);

            key->parttypid[i] = att->atttypid;
            key->parttypmod[i] = att->atttypmod;
            key->parttypcoll[i] = att->attcollation;
        }
        else
        {
            if (partexprs_item == NULL)
                elog(ERROR, "wrong number of partition key expressions");

            key->parttypid[i] = exprType(lfirst(partexprs_item));
            key->parttypmod[i] = exprTypmod(lfirst(partexprs_item));
            key->parttypcoll[i] = exprCollation(lfirst(partexprs_item));

            partexprs_item = lnext(key->partexprs, partexprs_item);
        }
        get_typlenbyvalalign(key->parttypid[i],
                             &key->parttyplen[i],
                             &key->parttypbyval[i],
                             &key->parttypalign[i]);

        ReleaseSysCache(opclasstup);
    }

    ReleaseSysCache(tuple);

    /* Assert that we're not leaking any old data during assignments below */
    Assert(relation->rd_partkeycxt == NULL);
    Assert(relation->rd_partkey == NULL);

    /*
     * Success --- reparent our context and make the relcache point to the
     * newly constructed key
     */
    MemoryContextSetParent(partkeycxt, CacheMemoryContext);
    relation->rd_partkeycxt = partkeycxt;
    relation->rd_partkey = key;
}

/*
 * RelationGetPartitionQual
 *
 * Returns a list of partition quals
 */
List *
RelationGetPartitionQual(Relation rel)
{
    /* Quick exit */
    if (!rel->rd_rel->relispartition)
        return NIL;

    return generate_partition_qual(rel);
}

/*
 * get_partition_qual_relid
 *
 * Returns an expression tree describing the passed-in relation's partition
 * constraint.
 *
 * If the relation is not found, or is not a partition, or there is no
 * partition constraint, return NULL.  We must guard against the first two
 * cases because this supports a SQL function that could be passed any OID.
 * The last case can happen even if relispartition is true, when a default
 * partition is the only partition.
 */
Expr *
get_partition_qual_relid(Oid relid)
{
    Expr       *result = NULL;

    /* Do the work only if this relation exists and is a partition. */
    if (get_rel_relispartition(relid))
    {
        Relation    rel = relation_open(relid, AccessShareLock);
        List       *and_args;

        and_args = generate_partition_qual(rel);

        /* Convert implicit-AND list format to boolean expression */
        if (and_args == NIL)
            result = NULL;
        else if (list_length(and_args) > 1)
            result = makeBoolExpr(AND_EXPR, and_args, -1);
        else
            result = linitial(and_args);

        /* Keep the lock, to allow safe deparsing against the rel by caller. */
        relation_close(rel, NoLock);
    }

    return result;
}

/*
 * generate_partition_qual
 *
 * Generate partition predicate from rel's partition bound expression. The
 * function returns a NIL list if there is no predicate.
 *
 * We cache a copy of the result in the relcache entry, after constructing
 * it using the caller's context.  This approach avoids leaking any data
 * into long-lived cache contexts, especially if we fail partway through.
 */
static List *
generate_partition_qual(Relation rel)
{
    HeapTuple   tuple;
    MemoryContext oldcxt;
    Datum       boundDatum;
    bool        isnull;
    List       *my_qual = NIL,
               *result = NIL;
    Oid         parentrelid;
    Relation    parent;

    /* Guard against stack overflow due to overly deep partition tree */
    check_stack_depth();

    /* If we already cached the result, just return a copy */
    if (rel->rd_partcheckvalid)
        return copyObject(rel->rd_partcheck);

    /*
     * Grab at least an AccessShareLock on the parent table.  Must do this
     * even if the partition has been partially detached, because transactions
     * concurrent with the detach might still be trying to use a partition
     * descriptor that includes it.
     */
    parentrelid = get_partition_parent(RelationGetRelid(rel), true);
    parent = relation_open(parentrelid, AccessShareLock);

    /* Get pg_class.relpartbound */
    tuple = SearchSysCache1(RELOID, RelationGetRelid(rel));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for relation %u",
             RelationGetRelid(rel));

    boundDatum = SysCacheGetAttr(RELOID, tuple,
                                 Anum_pg_class_relpartbound,
                                 &isnull);
    if (!isnull)
    {
        PartitionBoundSpec *bound;

        bound = castNode(PartitionBoundSpec,
                         stringToNode(TextDatumGetCString(boundDatum)));

        my_qual = get_qual_from_partbound(parent, bound);
    }

    ReleaseSysCache(tuple);

    /* Add the parent's quals to the list (if any) */
    if (parent->rd_rel->relispartition)
        result = list_concat(generate_partition_qual(parent), my_qual);
    else
        result = my_qual;

    /*
     * Change Vars to have partition's attnos instead of the parent's. We do
     * this after we concatenate the parent's quals, because we want every Var
     * in it to bear this relation's attnos. It's safe to assume varno = 1
     * here.
     */
    result = map_partition_varattnos(result, 1, rel, parent);

    /* Assert that we're not leaking any old data during assignments below */
    Assert(rel->rd_partcheckcxt == NULL);
    Assert(rel->rd_partcheck == NIL);

    /*
     * Save a copy in the relcache.  The order of these operations is fairly
     * critical to avoid memory leaks and ensure that we don't leave a corrupt
     * relcache entry if we fail partway through copyObject.
     *
     * If, as is definitely possible, the partcheck list is NIL, then we do
     * not need to make a context to hold it.
     */
    if (result != NIL)
    {
        rel->rd_partcheckcxt = AllocSetContextCreate(CacheMemoryContext,
                                                     "partition constraint",
                                                     ALLOCSET_SMALL_SIZES);
        MemoryContextCopyAndSetIdentifier(rel->rd_partcheckcxt,
                                          RelationGetRelationName(rel));
        oldcxt = MemoryContextSwitchTo(rel->rd_partcheckcxt);
        rel->rd_partcheck = copyObject(result);
        MemoryContextSwitchTo(oldcxt);
    }
    else
        rel->rd_partcheck = NIL;
    rel->rd_partcheckvalid = true;

    /* Keep the parent locked until commit */
    relation_close(parent, NoLock);

    /* Return the working copy to the caller */
    return result;
}