expandedrecord.c

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/*-------------------------------------------------------------------------
 *
 * expandedrecord.c
 *    Functions for manipulating composite expanded objects.
 *
 * This module supports "expanded objects" (cf. expandeddatum.h) that can
 * store values of named composite types, domains over named composite types,
 * and record types (registered or anonymous).
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/expandedrecord.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/detoast.h"
#include "access/heaptoast.h"
#include "access/htup_details.h"
#include "catalog/heap.h"
#include "catalog/pg_type.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/expandedrecord.h"
#include "utils/memutils.h"
#include "utils/typcache.h"
 
 
/* "Methods" required for an expanded object */
static Size ER_get_flat_size(ExpandedObjectHeader *eohptr);
static void ER_flatten_into(ExpandedObjectHeader *eohptr,
                            void *result, Size allocated_size);
 
static const ExpandedObjectMethods ER_methods =
{
    ER_get_flat_size,
    ER_flatten_into
};
 
/* Other local functions */
static void ER_mc_callback(void *arg);
static MemoryContext get_short_term_cxt(ExpandedRecordHeader *erh);
static void build_dummy_expanded_header(ExpandedRecordHeader *main_erh);
static pg_noinline void check_domain_for_new_field(ExpandedRecordHeader *erh,
                                                   int fnumber,
                                                   Datum newValue, bool isnull);
static pg_noinline void check_domain_for_new_tuple(ExpandedRecordHeader *erh,
                                                   HeapTuple tuple);
 
 
/*
 * Build an expanded record of the specified composite type
 *
 * type_id can be RECORDOID, but only if a positive typmod is given.
 *
 * The expanded record is initially "empty", having a state logically
 * equivalent to a NULL composite value (not ROW(NULL, NULL, ...)).
 * Note that this might not be a valid state for a domain type;
 * if the caller needs to check that, call
 * expanded_record_set_tuple(erh, NULL, false, false).
 *
 * The expanded object will be a child of parentcontext.
 */
ExpandedRecordHeader *
make_expanded_record_from_typeid(Oid type_id, int32 typmod,
                                 MemoryContext parentcontext)
{
    ExpandedRecordHeader *erh;
    int         flags = 0;
    TupleDesc   tupdesc;
    uint64      tupdesc_id;
    MemoryContext objcxt;
    char       *chunk;
 
    if (type_id != RECORDOID)
    {
        /*
         * Consult the typcache to see if it's a domain over composite, and in
         * any case to get the tupdesc and tupdesc identifier.
         */
        TypeCacheEntry *typentry;
 
        typentry = lookup_type_cache(type_id,
                                     TYPECACHE_TUPDESC |
                                     TYPECACHE_DOMAIN_BASE_INFO);
        if (typentry->typtype == TYPTYPE_DOMAIN)
        {
            flags |= ER_FLAG_IS_DOMAIN;
            typentry = lookup_type_cache(typentry->domainBaseType,
                                         TYPECACHE_TUPDESC);
        }
        if (typentry->tupDesc == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("type %s is not composite",
                            format_type_be(type_id))));
        tupdesc = typentry->tupDesc;
        tupdesc_id = typentry->tupDesc_identifier;
    }
    else
    {
        /*
         * For RECORD types, get the tupdesc and identifier from typcache.
         */
        tupdesc = lookup_rowtype_tupdesc(type_id, typmod);
        tupdesc_id = assign_record_type_identifier(type_id, typmod);
    }
 
    /*
     * Allocate private context for expanded object.  We use a regular-size
     * context, not a small one, to improve the odds that we can fit a tupdesc
     * into it without needing an extra malloc block.  (This code path doesn't
     * ever need to copy a tupdesc into the expanded record, but let's be
     * consistent with the other ways of making an expanded record.)
     */
    objcxt = AllocSetContextCreate(parentcontext,
                                   "expanded record",
                                   ALLOCSET_DEFAULT_SIZES);
 
    /*
     * Since we already know the number of fields in the tupdesc, we can
     * allocate the dvalues/dnulls arrays along with the record header.  This
     * is useless if we never need those arrays, but it costs almost nothing,
     * and it will save a palloc cycle if we do need them.
     */
    erh = (ExpandedRecordHeader *)
        MemoryContextAlloc(objcxt, MAXALIGN(sizeof(ExpandedRecordHeader))
                           + tupdesc->natts * (sizeof(Datum) + sizeof(bool)));
 
    /* Ensure all header fields are initialized to 0/null */
    memset(erh, 0, sizeof(ExpandedRecordHeader));
 
    EOH_init_header(&erh->hdr, &ER_methods, objcxt);
    erh->er_magic = ER_MAGIC;
 
    /* Set up dvalues/dnulls, with no valid contents as yet */
    chunk = (char *) erh + MAXALIGN(sizeof(ExpandedRecordHeader));
    erh->dvalues = (Datum *) chunk;
    erh->dnulls = (bool *) (chunk + tupdesc->natts * sizeof(Datum));
    erh->nfields = tupdesc->natts;
 
    /* Fill in composite-type identification info */
    erh->er_decltypeid = type_id;
    erh->er_typeid = tupdesc->tdtypeid;
    erh->er_typmod = tupdesc->tdtypmod;
    erh->er_tupdesc_id = tupdesc_id;
 
    erh->flags = flags;
 
    /*
     * If what we got from the typcache is a refcounted tupdesc, we need to
     * acquire our own refcount on it.  We manage the refcount with a memory
     * context callback rather than assuming that the CurrentResourceOwner is
     * longer-lived than this expanded object.
     */
    if (tupdesc->tdrefcount >= 0)
    {
        /* Register callback to release the refcount */
        erh->er_mcb.func = ER_mc_callback;
        erh->er_mcb.arg = erh;
        MemoryContextRegisterResetCallback(erh->hdr.eoh_context,
                                           &erh->er_mcb);
 
        /* And save the pointer */
        erh->er_tupdesc = tupdesc;
        tupdesc->tdrefcount++;
 
        /* If we called lookup_rowtype_tupdesc, release the pin it took */
        if (type_id == RECORDOID)
            ReleaseTupleDesc(tupdesc);
    }
    else
    {
        /*
         * If it's not refcounted, just assume it will outlive the expanded
         * object.  (This can happen for shared record types, for instance.)
         */
        erh->er_tupdesc = tupdesc;
    }
 
    /*
     * We don't set ER_FLAG_DVALUES_VALID or ER_FLAG_FVALUE_VALID, so the
     * record remains logically empty.
     */
 
    return erh;
}
 
/*
 * Build an expanded record of the rowtype defined by the tupdesc
 *
 * The tupdesc is copied if necessary (i.e., if we can't just bump its
 * reference count instead).
 *
 * The expanded record is initially "empty", having a state logically
 * equivalent to a NULL composite value (not ROW(NULL, NULL, ...)).
 *
 * The expanded object will be a child of parentcontext.
 */
ExpandedRecordHeader *
make_expanded_record_from_tupdesc(TupleDesc tupdesc,
                                  MemoryContext parentcontext)
{
    ExpandedRecordHeader *erh;
    uint64      tupdesc_id;
    MemoryContext objcxt;
    MemoryContext oldcxt;
    char       *chunk;
 
    if (tupdesc->tdtypeid != RECORDOID)
    {
        /*
         * If it's a named composite type (not RECORD), we prefer to reference
         * the typcache's copy of the tupdesc, which is guaranteed to be
         * refcounted (the given tupdesc might not be).  In any case, we need
         * to consult the typcache to get the correct tupdesc identifier.
         *
         * Note that tdtypeid couldn't be a domain type, so we need not
         * consider that case here.
         */
        TypeCacheEntry *typentry;
 
        typentry = lookup_type_cache(tupdesc->tdtypeid, TYPECACHE_TUPDESC);
        if (typentry->tupDesc == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("type %s is not composite",
                            format_type_be(tupdesc->tdtypeid))));
        tupdesc = typentry->tupDesc;
        tupdesc_id = typentry->tupDesc_identifier;
    }
    else
    {
        /*
         * For RECORD types, get the appropriate unique identifier (possibly
         * freshly assigned).
         */
        tupdesc_id = assign_record_type_identifier(tupdesc->tdtypeid,
                                                   tupdesc->tdtypmod);
    }
 
    /*
     * Allocate private context for expanded object.  We use a regular-size
     * context, not a small one, to improve the odds that we can fit a tupdesc
     * into it without needing an extra malloc block.
     */
    objcxt = AllocSetContextCreate(parentcontext,
                                   "expanded record",
                                   ALLOCSET_DEFAULT_SIZES);
 
    /*
     * Since we already know the number of fields in the tupdesc, we can
     * allocate the dvalues/dnulls arrays along with the record header.  This
     * is useless if we never need those arrays, but it costs almost nothing,
     * and it will save a palloc cycle if we do need them.
     */
    erh = (ExpandedRecordHeader *)
        MemoryContextAlloc(objcxt, MAXALIGN(sizeof(ExpandedRecordHeader))
                           + tupdesc->natts * (sizeof(Datum) + sizeof(bool)));
 
    /* Ensure all header fields are initialized to 0/null */
    memset(erh, 0, sizeof(ExpandedRecordHeader));
 
    EOH_init_header(&erh->hdr, &ER_methods, objcxt);
    erh->er_magic = ER_MAGIC;
 
    /* Set up dvalues/dnulls, with no valid contents as yet */
    chunk = (char *) erh + MAXALIGN(sizeof(ExpandedRecordHeader));
    erh->dvalues = (Datum *) chunk;
    erh->dnulls = (bool *) (chunk + tupdesc->natts * sizeof(Datum));
    erh->nfields = tupdesc->natts;
 
    /* Fill in composite-type identification info */
    erh->er_decltypeid = erh->er_typeid = tupdesc->tdtypeid;
    erh->er_typmod = tupdesc->tdtypmod;
    erh->er_tupdesc_id = tupdesc_id;
 
    /*
     * Copy tupdesc if needed, but we prefer to bump its refcount if possible.
     * We manage the refcount with a memory context callback rather than
     * assuming that the CurrentResourceOwner is longer-lived than this
     * expanded object.
     */
    if (tupdesc->tdrefcount >= 0)
    {
        /* Register callback to release the refcount */
        erh->er_mcb.func = ER_mc_callback;
        erh->er_mcb.arg = erh;
        MemoryContextRegisterResetCallback(erh->hdr.eoh_context,
                                           &erh->er_mcb);
 
        /* And save the pointer */
        erh->er_tupdesc = tupdesc;
        tupdesc->tdrefcount++;
    }
    else
    {
        /* Just copy it */
        oldcxt = MemoryContextSwitchTo(objcxt);
        erh->er_tupdesc = CreateTupleDescCopy(tupdesc);
        erh->flags |= ER_FLAG_TUPDESC_ALLOCED;
        MemoryContextSwitchTo(oldcxt);
    }
 
    /*
     * We don't set ER_FLAG_DVALUES_VALID or ER_FLAG_FVALUE_VALID, so the
     * record remains logically empty.
     */
 
    return erh;
}
 
/*
 * Build an expanded record of the same rowtype as the given expanded record
 *
 * This is faster than either of the above routines because we can bypass
 * typcache lookup(s).
 *
 * The expanded record is initially "empty" --- we do not copy whatever
 * tuple might be in the source expanded record.
 *
 * The expanded object will be a child of parentcontext.
 */
ExpandedRecordHeader *
make_expanded_record_from_exprecord(ExpandedRecordHeader *olderh,
                                    MemoryContext parentcontext)
{
    ExpandedRecordHeader *erh;
    TupleDesc   tupdesc = expanded_record_get_tupdesc(olderh);
    MemoryContext objcxt;
    MemoryContext oldcxt;
    char       *chunk;
 
    /*
     * Allocate private context for expanded object.  We use a regular-size
     * context, not a small one, to improve the odds that we can fit a tupdesc
     * into it without needing an extra malloc block.
     */
    objcxt = AllocSetContextCreate(parentcontext,
                                   "expanded record",
                                   ALLOCSET_DEFAULT_SIZES);
 
    /*
     * Since we already know the number of fields in the tupdesc, we can
     * allocate the dvalues/dnulls arrays along with the record header.  This
     * is useless if we never need those arrays, but it costs almost nothing,
     * and it will save a palloc cycle if we do need them.
     */
    erh = (ExpandedRecordHeader *)
        MemoryContextAlloc(objcxt, MAXALIGN(sizeof(ExpandedRecordHeader))
                           + tupdesc->natts * (sizeof(Datum) + sizeof(bool)));
 
    /* Ensure all header fields are initialized to 0/null */
    memset(erh, 0, sizeof(ExpandedRecordHeader));
 
    EOH_init_header(&erh->hdr, &ER_methods, objcxt);
    erh->er_magic = ER_MAGIC;
 
    /* Set up dvalues/dnulls, with no valid contents as yet */
    chunk = (char *) erh + MAXALIGN(sizeof(ExpandedRecordHeader));
    erh->dvalues = (Datum *) chunk;
    erh->dnulls = (bool *) (chunk + tupdesc->natts * sizeof(Datum));
    erh->nfields = tupdesc->natts;
 
    /* Fill in composite-type identification info */
    erh->er_decltypeid = olderh->er_decltypeid;
    erh->er_typeid = olderh->er_typeid;
    erh->er_typmod = olderh->er_typmod;
    erh->er_tupdesc_id = olderh->er_tupdesc_id;
 
    /* The only flag bit that transfers over is IS_DOMAIN */
    erh->flags = olderh->flags & ER_FLAG_IS_DOMAIN;
 
    /*
     * Copy tupdesc if needed, but we prefer to bump its refcount if possible.
     * We manage the refcount with a memory context callback rather than
     * assuming that the CurrentResourceOwner is longer-lived than this
     * expanded object.
     */
    if (tupdesc->tdrefcount >= 0)
    {
        /* Register callback to release the refcount */
        erh->er_mcb.func = ER_mc_callback;
        erh->er_mcb.arg = erh;
        MemoryContextRegisterResetCallback(erh->hdr.eoh_context,
                                           &erh->er_mcb);
 
        /* And save the pointer */
        erh->er_tupdesc = tupdesc;
        tupdesc->tdrefcount++;
    }
    else if (olderh->flags & ER_FLAG_TUPDESC_ALLOCED)
    {
        /* We need to make our own copy of the tupdesc */
        oldcxt = MemoryContextSwitchTo(objcxt);
        erh->er_tupdesc = CreateTupleDescCopy(tupdesc);
        erh->flags |= ER_FLAG_TUPDESC_ALLOCED;
        MemoryContextSwitchTo(oldcxt);
    }
    else
    {
        /*
         * Assume the tupdesc will outlive this expanded object, just like
         * we're assuming it will outlive the source object.
         */
        erh->er_tupdesc = tupdesc;
    }
 
    /*
     * We don't set ER_FLAG_DVALUES_VALID or ER_FLAG_FVALUE_VALID, so the
     * record remains logically empty.
     */
 
    return erh;
}
 
/*
 * Insert given tuple as the value of the expanded record
 *
 * It is caller's responsibility that the tuple matches the record's
 * previously-assigned rowtype.  (However domain constraints, if any,
 * will be checked here.)
 *
 * The tuple is physically copied into the expanded record's local storage
 * if "copy" is true, otherwise it's caller's responsibility that the tuple
 * will live as long as the expanded record does.
 *
 * Out-of-line field values in the tuple are automatically inlined if
 * "expand_external" is true, otherwise not.  (The combination copy = false,
 * expand_external = true is not sensible and not supported.)
 *
 * Alternatively, tuple can be NULL, in which case we just set the expanded
 * record to be empty.
 */
void
expanded_record_set_tuple(ExpandedRecordHeader *erh,
                          HeapTuple tuple,
                          bool copy,
                          bool expand_external)
{
    int         oldflags;
    HeapTuple   oldtuple;
    char       *oldfstartptr;
    char       *oldfendptr;
    int         newflags;
    HeapTuple   newtuple;
    MemoryContext oldcxt;
 
    /* Shouldn't ever be trying to assign new data to a dummy header */
    Assert(!(erh->flags & ER_FLAG_IS_DUMMY));
 
    /*
     * Before performing the assignment, see if result will satisfy domain.
     */
    if (erh->flags & ER_FLAG_IS_DOMAIN)
        check_domain_for_new_tuple(erh, tuple);
 
    /*
     * If we need to get rid of out-of-line field values, do so, using the
     * short-term context to avoid leaking whatever cruft the toast fetch
     * might generate.
     */
    if (expand_external && tuple)
    {
        /* Assert caller didn't ask for unsupported case */
        Assert(copy);
        if (HeapTupleHasExternal(tuple))
        {
            oldcxt = MemoryContextSwitchTo(get_short_term_cxt(erh));
            tuple = toast_flatten_tuple(tuple, erh->er_tupdesc);
            MemoryContextSwitchTo(oldcxt);
        }
        else
            expand_external = false;    /* need not clean up below */
    }
 
    /*
     * Initialize new flags, keeping only non-data status bits.
     */
    oldflags = erh->flags;
    newflags = oldflags & ER_FLAGS_NON_DATA;
 
    /*
     * Copy tuple into local storage if needed.  We must be sure this succeeds
     * before we start to modify the expanded record's state.
     */
    if (copy && tuple)
    {
        oldcxt = MemoryContextSwitchTo(erh->hdr.eoh_context);
        newtuple = heap_copytuple(tuple);
        newflags |= ER_FLAG_FVALUE_ALLOCED;
        MemoryContextSwitchTo(oldcxt);
 
        /* We can now flush anything that detoasting might have leaked. */
        if (expand_external)
            MemoryContextReset(erh->er_short_term_cxt);
    }
    else
        newtuple = tuple;
 
    /* Make copies of fields we're about to overwrite */
    oldtuple = erh->fvalue;
    oldfstartptr = erh->fstartptr;
    oldfendptr = erh->fendptr;
 
    /*
     * It's now safe to update the expanded record's state.
     */
    if (newtuple)
    {
        /* Save flat representation */
        erh->fvalue = newtuple;
        erh->fstartptr = (char *) newtuple->t_data;
        erh->fendptr = ((char *) newtuple->t_data) + newtuple->t_len;
        newflags |= ER_FLAG_FVALUE_VALID;
 
        /* Remember if we have any out-of-line field values */
        if (HeapTupleHasExternal(newtuple))
            newflags |= ER_FLAG_HAVE_EXTERNAL;
    }
    else
    {
        erh->fvalue = NULL;
        erh->fstartptr = erh->fendptr = NULL;
    }
 
    erh->flags = newflags;
 
    /* Reset flat-size info; we don't bother to make it valid now */
    erh->flat_size = 0;
 
    /*
     * Now, release any storage belonging to old field values.  It's safe to
     * do this because ER_FLAG_DVALUES_VALID is no longer set in erh->flags;
     * even if we fail partway through, the record is valid, and at worst
     * we've failed to reclaim some space.
     */
    if (oldflags & ER_FLAG_DVALUES_ALLOCED)
    {
        TupleDesc   tupdesc = erh->er_tupdesc;
        int         i;
 
        for (i = 0; i < erh->nfields; i++)
        {
            if (!erh->dnulls[i] &&
                !(TupleDescCompactAttr(tupdesc, i)->attbyval))
            {
                char       *oldValue = (char *) DatumGetPointer(erh->dvalues[i]);
 
                if (oldValue < oldfstartptr || oldValue >= oldfendptr)
                    pfree(oldValue);
            }
        }
    }
 
    /* Likewise free the old tuple, if it was locally allocated */
    if (oldflags & ER_FLAG_FVALUE_ALLOCED)
        heap_freetuple(oldtuple);
 
    /* We won't make a new deconstructed representation until/unless needed */
}
 
/*
 * make_expanded_record_from_datum: build expanded record from composite Datum
 *
 * This combines the functions of make_expanded_record_from_typeid and
 * expanded_record_set_tuple.  However, we do not force a lookup of the
 * tupdesc immediately, reasoning that it might never be needed.
 *
 * The expanded object will be a child of parentcontext.
 *
 * Note: a composite datum cannot self-identify as being of a domain type,
 * so we need not consider domain cases here.
 */
Datum
make_expanded_record_from_datum(Datum recorddatum, MemoryContext parentcontext)
{
    ExpandedRecordHeader *erh;
    HeapTupleHeader tuphdr;
    HeapTupleData tmptup;
    HeapTuple   newtuple;
    MemoryContext objcxt;
    MemoryContext oldcxt;
 
    /*
     * Allocate private context for expanded object.  We use a regular-size
     * context, not a small one, to improve the odds that we can fit a tupdesc
     * into it without needing an extra malloc block.
     */
    objcxt = AllocSetContextCreate(parentcontext,
                                   "expanded record",
                                   ALLOCSET_DEFAULT_SIZES);
 
    /* Set up expanded record header, initializing fields to 0/null */
    erh = (ExpandedRecordHeader *)
        MemoryContextAllocZero(objcxt, sizeof(ExpandedRecordHeader));
 
    EOH_init_header(&erh->hdr, &ER_methods, objcxt);
    erh->er_magic = ER_MAGIC;
 
    /*
     * Detoast and copy source record into private context, as a HeapTuple.
     * (If we actually have to detoast the source, we'll leak some memory in
     * the caller's context, but it doesn't seem worth worrying about.)
     */
    tuphdr = DatumGetHeapTupleHeader(recorddatum);
 
    tmptup.t_len = HeapTupleHeaderGetDatumLength(tuphdr);
    ItemPointerSetInvalid(&(tmptup.t_self));
    tmptup.t_tableOid = InvalidOid;
    tmptup.t_data = tuphdr;
 
    oldcxt = MemoryContextSwitchTo(objcxt);
    newtuple = heap_copytuple(&tmptup);
    erh->flags |= ER_FLAG_FVALUE_ALLOCED;
    MemoryContextSwitchTo(oldcxt);
 
    /* Fill in composite-type identification info */
    erh->er_decltypeid = erh->er_typeid = HeapTupleHeaderGetTypeId(tuphdr);
    erh->er_typmod = HeapTupleHeaderGetTypMod(tuphdr);
 
    /* remember we have a flat representation */
    erh->fvalue = newtuple;
    erh->fstartptr = (char *) newtuple->t_data;
    erh->fendptr = ((char *) newtuple->t_data) + newtuple->t_len;
    erh->flags |= ER_FLAG_FVALUE_VALID;
 
    /* Shouldn't need to set ER_FLAG_HAVE_EXTERNAL */
    Assert(!HeapTupleHeaderHasExternal(tuphdr));
 
    /*
     * We won't look up the tupdesc till we have to, nor make a deconstructed
     * representation.  We don't have enough info to fill flat_size and
     * friends, either.
     */
 
    /* return a R/W pointer to the expanded record */
    return EOHPGetRWDatum(&erh->hdr);
}
 
/*
 * get_flat_size method for expanded records
 *
 * Note: call this in a reasonably short-lived memory context, in case of
 * memory leaks from activities such as detoasting.
 */
static Size
ER_get_flat_size(ExpandedObjectHeader *eohptr)
{
    ExpandedRecordHeader *erh = (ExpandedRecordHeader *) eohptr;
    TupleDesc   tupdesc;
    Size        len;
    Size        data_len;
    int         hoff;
    bool        hasnull;
    int         i;
 
    Assert(erh->er_magic == ER_MAGIC);
 
    /*
     * The flat representation has to be a valid composite datum.  Make sure
     * that we have a registered, not anonymous, RECORD type.
     */
    if (erh->er_typeid == RECORDOID &&
        erh->er_typmod < 0)
    {
        tupdesc = expanded_record_get_tupdesc(erh);
        assign_record_type_typmod(tupdesc);
        erh->er_typmod = tupdesc->tdtypmod;
    }
 
    /*
     * If we have a valid flattened value without out-of-line fields, we can
     * just use it as-is.
     */
    if (erh->flags & ER_FLAG_FVALUE_VALID &&
        !(erh->flags & ER_FLAG_HAVE_EXTERNAL))
        return erh->fvalue->t_len;
 
    /* If we have a cached size value, believe that */
    if (erh->flat_size)
        return erh->flat_size;
 
    /* If we haven't yet deconstructed the tuple, do that */
    if (!(erh->flags & ER_FLAG_DVALUES_VALID))
        deconstruct_expanded_record(erh);
 
    /* Tuple descriptor must be valid by now */
    tupdesc = erh->er_tupdesc;
 
    /*
     * Composite datums mustn't contain any out-of-line values.
     */
    if (erh->flags & ER_FLAG_HAVE_EXTERNAL)
    {
        for (i = 0; i < erh->nfields; i++)
        {
            CompactAttribute *attr = TupleDescCompactAttr(tupdesc, i);
 
            if (!erh->dnulls[i] &&
                !attr->attbyval && attr->attlen == -1 &&
                VARATT_IS_EXTERNAL(DatumGetPointer(erh->dvalues[i])))
            {
                /*
                 * expanded_record_set_field_internal can do the actual work
                 * of detoasting.  It needn't recheck domain constraints.
                 */
                expanded_record_set_field_internal(erh, i + 1,
                                                   erh->dvalues[i], false,
                                                   true,
                                                   false);
            }
        }
 
        /*
         * We have now removed all external field values, so we can clear the
         * flag about them.  This won't cause ER_flatten_into() to mistakenly
         * take the fast path, since expanded_record_set_field() will have
         * cleared ER_FLAG_FVALUE_VALID.
         */
        erh->flags &= ~ER_FLAG_HAVE_EXTERNAL;
    }
 
    /* Test if we currently have any null values */
    hasnull = false;
    for (i = 0; i < erh->nfields; i++)
    {
        if (erh->dnulls[i])
        {
            hasnull = true;
            break;
        }
    }
 
    /* Determine total space needed */
    len = offsetof(HeapTupleHeaderData, t_bits);
 
    if (hasnull)
        len += BITMAPLEN(tupdesc->natts);
 
    hoff = len = MAXALIGN(len); /* align user data safely */
 
    data_len = heap_compute_data_size(tupdesc, erh->dvalues, erh->dnulls);
 
    len += data_len;
 
    /* Cache for next time */
    erh->flat_size = len;
    erh->data_len = data_len;
    erh->hoff = hoff;
    erh->hasnull = hasnull;
 
    return len;
}
 
/*
 * flatten_into method for expanded records
 */
static void
ER_flatten_into(ExpandedObjectHeader *eohptr,
                void *result, Size allocated_size)
{
    ExpandedRecordHeader *erh = (ExpandedRecordHeader *) eohptr;
    HeapTupleHeader tuphdr = (HeapTupleHeader) result;
    TupleDesc   tupdesc;
 
    Assert(erh->er_magic == ER_MAGIC);
 
    /* Easy if we have a valid flattened value without out-of-line fields */
    if (erh->flags & ER_FLAG_FVALUE_VALID &&
        !(erh->flags & ER_FLAG_HAVE_EXTERNAL))
    {
        Assert(allocated_size == erh->fvalue->t_len);
        memcpy(tuphdr, erh->fvalue->t_data, allocated_size);
        /* The original flattened value might not have datum header fields */
        HeapTupleHeaderSetDatumLength(tuphdr, allocated_size);
        HeapTupleHeaderSetTypeId(tuphdr, erh->er_typeid);
        HeapTupleHeaderSetTypMod(tuphdr, erh->er_typmod);
        return;
    }
 
    /* Else allocation should match previous get_flat_size result */
    Assert(allocated_size == erh->flat_size);
 
    /* We'll need the tuple descriptor */
    tupdesc = expanded_record_get_tupdesc(erh);
 
    /* We must ensure that any pad space is zero-filled */
    memset(tuphdr, 0, allocated_size);
 
    /* Set up header fields of composite Datum */
    HeapTupleHeaderSetDatumLength(tuphdr, allocated_size);
    HeapTupleHeaderSetTypeId(tuphdr, erh->er_typeid);
    HeapTupleHeaderSetTypMod(tuphdr, erh->er_typmod);
    /* We also make sure that t_ctid is invalid unless explicitly set */
    ItemPointerSetInvalid(&(tuphdr->t_ctid));
 
    HeapTupleHeaderSetNatts(tuphdr, tupdesc->natts);
    tuphdr->t_hoff = erh->hoff;
 
    /* And fill the data area from dvalues/dnulls */
    heap_fill_tuple(tupdesc,
                    erh->dvalues,
                    erh->dnulls,
                    (char *) tuphdr + erh->hoff,
                    erh->data_len,
                    &tuphdr->t_infomask,
                    (erh->hasnull ? tuphdr->t_bits : NULL));
}
 
/*
 * Look up the tupdesc for the expanded record's actual type
 *
 * Note: code internal to this module is allowed to just fetch
 * erh->er_tupdesc if ER_FLAG_DVALUES_VALID is set; otherwise it should call
 * expanded_record_get_tupdesc.  This function is the out-of-line portion
 * of expanded_record_get_tupdesc.
 */
TupleDesc
expanded_record_fetch_tupdesc(ExpandedRecordHeader *erh)
{
    TupleDesc   tupdesc;
 
    /* Easy if we already have it (but caller should have checked already) */
    if (erh->er_tupdesc)
        return erh->er_tupdesc;
 
    /* Lookup the composite type's tupdesc using the typcache */
    tupdesc = lookup_rowtype_tupdesc(erh->er_typeid, erh->er_typmod);
 
    /*
     * If it's a refcounted tupdesc rather than a statically allocated one, we
     * want to manage the refcount with a memory context callback rather than
     * assuming that the CurrentResourceOwner is longer-lived than this
     * expanded object.
     */
    if (tupdesc->tdrefcount >= 0)
    {
        /* Register callback if we didn't already */
        if (erh->er_mcb.arg == NULL)
        {
            erh->er_mcb.func = ER_mc_callback;
            erh->er_mcb.arg = erh;
            MemoryContextRegisterResetCallback(erh->hdr.eoh_context,
                                               &erh->er_mcb);
        }
 
        /* Remember our own pointer */
        erh->er_tupdesc = tupdesc;
        tupdesc->tdrefcount++;
 
        /* Release the pin lookup_rowtype_tupdesc acquired */
        ReleaseTupleDesc(tupdesc);
    }
    else
    {
        /* Just remember the pointer */
        erh->er_tupdesc = tupdesc;
    }
 
    /* In either case, fetch the process-global ID for this tupdesc */
    erh->er_tupdesc_id = assign_record_type_identifier(tupdesc->tdtypeid,
                                                       tupdesc->tdtypmod);
 
    return tupdesc;
}
 
/*
 * Get a HeapTuple representing the current value of the expanded record
 *
 * If valid, the originally stored tuple is returned, so caller must not
 * scribble on it.  Otherwise, we return a HeapTuple created in the current
 * memory context.  In either case, no attempt has been made to inline
 * out-of-line toasted values, so the tuple isn't usable as a composite
 * datum.
 *
 * Returns NULL if expanded record is empty.
 */
HeapTuple
expanded_record_get_tuple(ExpandedRecordHeader *erh)
{
    /* Easy case if we still have original tuple */
    if (erh->flags & ER_FLAG_FVALUE_VALID)
        return erh->fvalue;
 
    /* Else just build a tuple from datums */
    if (erh->flags & ER_FLAG_DVALUES_VALID)
        return heap_form_tuple(erh->er_tupdesc, erh->dvalues, erh->dnulls);
 
    /* Expanded record is empty */
    return NULL;
}
 
/*
 * Memory context reset callback for cleaning up external resources
 */
static void
ER_mc_callback(void *arg)
{
    ExpandedRecordHeader *erh = (ExpandedRecordHeader *) arg;
    TupleDesc   tupdesc = erh->er_tupdesc;
 
    /* Release our privately-managed tupdesc refcount, if any */
    if (tupdesc)
    {
        erh->er_tupdesc = NULL; /* just for luck */
        if (tupdesc->tdrefcount > 0)
        {
            if (--tupdesc->tdrefcount == 0)
                FreeTupleDesc(tupdesc);
        }
    }
}
 
/*
 * DatumGetExpandedRecord: get a writable expanded record from an input argument
 *
 * Caution: if the input is a read/write pointer, this returns the input
 * argument; so callers must be sure that their changes are "safe", that is
 * they cannot leave the record in a corrupt state.
 */
ExpandedRecordHeader *
DatumGetExpandedRecord(Datum d)
{
    /* If it's a writable expanded record already, just return it */
    if (VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)))
    {
        ExpandedRecordHeader *erh = (ExpandedRecordHeader *) DatumGetEOHP(d);
 
        Assert(erh->er_magic == ER_MAGIC);
        return erh;
    }
 
    /* Else expand the hard way */
    d = make_expanded_record_from_datum(d, CurrentMemoryContext);
    return (ExpandedRecordHeader *) DatumGetEOHP(d);
}
 
/*
 * Create the Datum/isnull representation of an expanded record object
 * if we didn't do so already.  After calling this, it's OK to read the
 * dvalues/dnulls arrays directly, rather than going through get_field.
 *
 * Note that if the object is currently empty ("null"), this will change
 * it to represent a row of nulls.
 */
void
deconstruct_expanded_record(ExpandedRecordHeader *erh)
{
    TupleDesc   tupdesc;
    Datum      *dvalues;
    bool       *dnulls;
    int         nfields;
 
    if (erh->flags & ER_FLAG_DVALUES_VALID)
        return;                 /* already valid, nothing to do */
 
    /* We'll need the tuple descriptor */
    tupdesc = expanded_record_get_tupdesc(erh);
 
    /*
     * Allocate arrays in private context, if we don't have them already.  We
     * don't expect to see a change in nfields here, so while we cope if it
     * happens, we don't bother avoiding a leak of the old arrays (which might
     * not be separately palloc'd, anyway).
     */
    nfields = tupdesc->natts;
    if (erh->dvalues == NULL || erh->nfields != nfields)
    {
        char       *chunk;
 
        /*
         * To save a palloc cycle, we allocate both the Datum and isnull
         * arrays in one palloc chunk.
         */
        chunk = MemoryContextAlloc(erh->hdr.eoh_context,
                                   nfields * (sizeof(Datum) + sizeof(bool)));
        dvalues = (Datum *) chunk;
        dnulls = (bool *) (chunk + nfields * sizeof(Datum));
        erh->dvalues = dvalues;
        erh->dnulls = dnulls;
        erh->nfields = nfields;
    }
    else
    {
        dvalues = erh->dvalues;
        dnulls = erh->dnulls;
    }
 
    if (erh->flags & ER_FLAG_FVALUE_VALID)
    {
        /* Deconstruct tuple */
        heap_deform_tuple(erh->fvalue, tupdesc, dvalues, dnulls);
    }
    else
    {
        /* If record was empty, instantiate it as a row of nulls */
        memset(dvalues, 0, nfields * sizeof(Datum));
        memset(dnulls, true, nfields * sizeof(bool));
    }
 
    /* Mark the dvalues as valid */
    erh->flags |= ER_FLAG_DVALUES_VALID;
}
 
/*
 * Look up a record field by name
 *
 * If there is a field named "fieldname", fill in the contents of finfo
 * and return "true".  Else return "false" without changing *finfo.
 */
bool
expanded_record_lookup_field(ExpandedRecordHeader *erh, const char *fieldname,
                             ExpandedRecordFieldInfo *finfo)
{
    TupleDesc   tupdesc;
    int         fno;
    Form_pg_attribute attr;
    const FormData_pg_attribute *sysattr;
 
    tupdesc = expanded_record_get_tupdesc(erh);
 
    /* First, check user-defined attributes */
    for (fno = 0; fno < tupdesc->natts; fno++)
    {
        attr = TupleDescAttr(tupdesc, fno);
        if (namestrcmp(&attr->attname, fieldname) == 0 &&
            !attr->attisdropped)
        {
            finfo->fnumber = attr->attnum;
            finfo->ftypeid = attr->atttypid;
            finfo->ftypmod = attr->atttypmod;
            finfo->fcollation = attr->attcollation;
            return true;
        }
    }
 
    /* How about system attributes? */
    sysattr = SystemAttributeByName(fieldname);
    if (sysattr != NULL)
    {
        finfo->fnumber = sysattr->attnum;
        finfo->ftypeid = sysattr->atttypid;
        finfo->ftypmod = sysattr->atttypmod;
        finfo->fcollation = sysattr->attcollation;
        return true;
    }
 
    return false;
}
 
/*
 * Fetch value of record field
 *
 * expanded_record_get_field is the frontend for this; it handles the
 * easy inline-able cases.
 */
Datum
expanded_record_fetch_field(ExpandedRecordHeader *erh, int fnumber,
                            bool *isnull)
{
    if (fnumber > 0)
    {
        /* Empty record has null fields */
        if (ExpandedRecordIsEmpty(erh))
        {
            *isnull = true;
            return (Datum) 0;
        }
        /* Make sure we have deconstructed form */
        deconstruct_expanded_record(erh);
        /* Out-of-range field number reads as null */
        if (unlikely(fnumber > erh->nfields))
        {
            *isnull = true;
            return (Datum) 0;
        }
        *isnull = erh->dnulls[fnumber - 1];
        return erh->dvalues[fnumber - 1];
    }
    else
    {
        /* System columns read as null if we haven't got flat tuple */
        if (erh->fvalue == NULL)
        {
            *isnull = true;
            return (Datum) 0;
        }
        /* heap_getsysattr doesn't actually use tupdesc, so just pass null */
        return heap_getsysattr(erh->fvalue, fnumber, NULL, isnull);
    }
}
 
/*
 * Set value of record field
 *
 * If the expanded record is of domain type, the assignment will be rejected
 * (without changing the record's state) if the domain's constraints would
 * be violated.
 *
 * If expand_external is true and newValue is an out-of-line value, we'll
 * forcibly detoast it so that the record does not depend on external storage.
 *
 * Internal callers can pass check_constraints = false to skip application
 * of domain constraints.  External callers should never do that.
 */
void
expanded_record_set_field_internal(ExpandedRecordHeader *erh, int fnumber,
                                   Datum newValue, bool isnull,
                                   bool expand_external,
                                   bool check_constraints)
{
    TupleDesc   tupdesc;
    CompactAttribute *attr;
    Datum      *dvalues;
    bool       *dnulls;
    char       *oldValue;
 
    /*
     * Shouldn't ever be trying to assign new data to a dummy header, except
     * in the case of an internal call for field inlining.
     */
    Assert(!(erh->flags & ER_FLAG_IS_DUMMY) || !check_constraints);
 
    /* Before performing the assignment, see if result will satisfy domain */
    if ((erh->flags & ER_FLAG_IS_DOMAIN) && check_constraints)
        check_domain_for_new_field(erh, fnumber, newValue, isnull);
 
    /* If we haven't yet deconstructed the tuple, do that */
    if (!(erh->flags & ER_FLAG_DVALUES_VALID))
        deconstruct_expanded_record(erh);
 
    /* Tuple descriptor must be valid by now */
    tupdesc = erh->er_tupdesc;
    Assert(erh->nfields == tupdesc->natts);
 
    /* Caller error if fnumber is system column or nonexistent column */
    if (unlikely(fnumber <= 0 || fnumber > erh->nfields))
        elog(ERROR, "cannot assign to field %d of expanded record", fnumber);
 
    /*
     * Copy new field value into record's context, and deal with detoasting,
     * if needed.
     */
    attr = TupleDescCompactAttr(tupdesc, fnumber - 1);
    if (!isnull && !attr->attbyval)
    {
        MemoryContext oldcxt;
 
        /* If requested, detoast any external value */
        if (expand_external)
        {
            if (attr->attlen == -1 &&
                VARATT_IS_EXTERNAL(DatumGetPointer(newValue)))
            {
                /* Detoasting should be done in short-lived context. */
                oldcxt = MemoryContextSwitchTo(get_short_term_cxt(erh));
                newValue = PointerGetDatum(detoast_external_attr((struct varlena *) DatumGetPointer(newValue)));
                MemoryContextSwitchTo(oldcxt);
            }
            else
                expand_external = false;    /* need not clean up below */
        }
 
        /* Copy value into record's context */
        oldcxt = MemoryContextSwitchTo(erh->hdr.eoh_context);
        newValue = datumCopy(newValue, false, attr->attlen);
        MemoryContextSwitchTo(oldcxt);
 
        /* We can now flush anything that detoasting might have leaked */
        if (expand_external)
            MemoryContextReset(erh->er_short_term_cxt);
 
        /* Remember that we have field(s) that may need to be pfree'd */
        erh->flags |= ER_FLAG_DVALUES_ALLOCED;
 
        /*
         * While we're here, note whether it's an external toasted value,
         * because that could mean we need to inline it later.  (Think not to
         * merge this into the previous expand_external logic: datumCopy could
         * by itself have made the value non-external.)
         */
        if (attr->attlen == -1 &&
            VARATT_IS_EXTERNAL(DatumGetPointer(newValue)))
            erh->flags |= ER_FLAG_HAVE_EXTERNAL;
    }
 
    /*
     * We're ready to make irreversible changes.
     */
    dvalues = erh->dvalues;
    dnulls = erh->dnulls;
 
    /* Flattened value will no longer represent record accurately */
    erh->flags &= ~ER_FLAG_FVALUE_VALID;
    /* And we don't know the flattened size either */
    erh->flat_size = 0;
 
    /* Grab old field value for pfree'ing, if needed. */
    if (!attr->attbyval && !dnulls[fnumber - 1])
        oldValue = (char *) DatumGetPointer(dvalues[fnumber - 1]);
    else
        oldValue = NULL;
 
    /* And finally we can insert the new field. */
    dvalues[fnumber - 1] = newValue;
    dnulls[fnumber - 1] = isnull;
 
    /*
     * Free old field if needed; this keeps repeated field replacements from
     * bloating the record's storage.  If the pfree somehow fails, it won't
     * corrupt the record.
     *
     * If we're updating a dummy header, we can't risk pfree'ing the old
     * value, because most likely the expanded record's main header still has
     * a pointer to it.  This won't result in any sustained memory leak, since
     * whatever we just allocated here is in the short-lived domain check
     * context.
     */
    if (oldValue && !(erh->flags & ER_FLAG_IS_DUMMY))
    {
        /* Don't try to pfree a part of the original flat record */
        if (oldValue < erh->fstartptr || oldValue >= erh->fendptr)
            pfree(oldValue);
    }
}
 
/*
 * Set all record field(s)
 *
 * Caller must ensure that the provided datums are of the right types
 * to match the record's previously assigned rowtype.
 *
 * If expand_external is true, we'll forcibly detoast out-of-line field values
 * so that the record does not depend on external storage.
 *
 * Unlike repeated application of expanded_record_set_field(), this does not
 * guarantee to leave the expanded record in a non-corrupt state in event
 * of an error.  Typically it would only be used for initializing a new
 * expanded record.  Also, because we expect this to be applied at most once
 * in the lifespan of an expanded record, we do not worry about any cruft
 * that detoasting might leak.
 */
void
expanded_record_set_fields(ExpandedRecordHeader *erh,
                           const Datum *newValues, const bool *isnulls,
                           bool expand_external)
{
    TupleDesc   tupdesc;
    Datum      *dvalues;
    bool       *dnulls;
    int         fnumber;
    MemoryContext oldcxt;
 
    /* Shouldn't ever be trying to assign new data to a dummy header */
    Assert(!(erh->flags & ER_FLAG_IS_DUMMY));
 
    /* If we haven't yet deconstructed the tuple, do that */
    if (!(erh->flags & ER_FLAG_DVALUES_VALID))
        deconstruct_expanded_record(erh);
 
    /* Tuple descriptor must be valid by now */
    tupdesc = erh->er_tupdesc;
    Assert(erh->nfields == tupdesc->natts);
 
    /* Flattened value will no longer represent record accurately */
    erh->flags &= ~ER_FLAG_FVALUE_VALID;
    /* And we don't know the flattened size either */
    erh->flat_size = 0;
 
    oldcxt = MemoryContextSwitchTo(erh->hdr.eoh_context);
 
    dvalues = erh->dvalues;
    dnulls = erh->dnulls;
 
    for (fnumber = 0; fnumber < erh->nfields; fnumber++)
    {
        CompactAttribute *attr = TupleDescCompactAttr(tupdesc, fnumber);
        Datum       newValue;
        bool        isnull;
 
        /* Ignore dropped columns */
        if (attr->attisdropped)
            continue;
 
        newValue = newValues[fnumber];
        isnull = isnulls[fnumber];
 
        if (!attr->attbyval)
        {
            /*
             * Copy new field value into record's context, and deal with
             * detoasting, if needed.
             */
            if (!isnull)
            {
                /* Is it an external toasted value? */
                if (attr->attlen == -1 &&
                    VARATT_IS_EXTERNAL(DatumGetPointer(newValue)))
                {
                    if (expand_external)
                    {
                        /* Detoast as requested while copying the value */
                        newValue = PointerGetDatum(detoast_external_attr((struct varlena *) DatumGetPointer(newValue)));
                    }
                    else
                    {
                        /* Just copy the value */
                        newValue = datumCopy(newValue, false, -1);
                        /* If it's still external, remember that */
                        if (VARATT_IS_EXTERNAL(DatumGetPointer(newValue)))
                            erh->flags |= ER_FLAG_HAVE_EXTERNAL;
                    }
                }
                else
                {
                    /* Not an external value, just copy it */
                    newValue = datumCopy(newValue, false, attr->attlen);
                }
 
                /* Remember that we have field(s) that need to be pfree'd */
                erh->flags |= ER_FLAG_DVALUES_ALLOCED;
            }
 
            /*
             * Free old field value, if any (not likely, since really we ought
             * to be inserting into an empty record).
             */
            if (unlikely(!dnulls[fnumber]))
            {
                char       *oldValue;
 
                oldValue = (char *) DatumGetPointer(dvalues[fnumber]);
                /* Don't try to pfree a part of the original flat record */
                if (oldValue < erh->fstartptr || oldValue >= erh->fendptr)
                    pfree(oldValue);
            }
        }
 
        /* And finally we can insert the new field. */
        dvalues[fnumber] = newValue;
        dnulls[fnumber] = isnull;
    }
 
    /*
     * Because we don't guarantee atomicity of set_fields(), we can just leave
     * checking of domain constraints to occur as the final step; if it throws
     * an error, too bad.
     */
    if (erh->flags & ER_FLAG_IS_DOMAIN)
    {
        /* We run domain_check in a short-lived context to limit cruft */
        MemoryContextSwitchTo(get_short_term_cxt(erh));
 
        domain_check(ExpandedRecordGetRODatum(erh), false,
                     erh->er_decltypeid,
                     &erh->er_domaininfo,
                     erh->hdr.eoh_context);
    }
 
    MemoryContextSwitchTo(oldcxt);
}
 
/*
 * Construct (or reset) working memory context for short-term operations.
 *
 * This context is used for domain check evaluation and for detoasting.
 *
 * If we don't have a short-lived memory context, make one; if we have one,
 * reset it to get rid of any leftover cruft.  (It is a tad annoying to need a
 * whole context for this, since it will often go unused --- but it's hard to
 * avoid memory leaks otherwise.  We can make the context small, at least.)
 */
static MemoryContext
get_short_term_cxt(ExpandedRecordHeader *erh)
{
    if (erh->er_short_term_cxt == NULL)
        erh->er_short_term_cxt =
            AllocSetContextCreate(erh->hdr.eoh_context,
                                  "expanded record short-term context",
                                  ALLOCSET_SMALL_SIZES);
    else
        MemoryContextReset(erh->er_short_term_cxt);
    return erh->er_short_term_cxt;
}
 
/*
 * Construct "dummy header" for checking domain constraints.
 *
 * Since we don't want to modify the state of the expanded record until
 * we've validated the constraints, our approach is to set up a dummy
 * record header containing the new field value(s) and then pass that to
 * domain_check.  We retain the dummy header as part of the expanded
 * record's state to save palloc cycles, but reinitialize (most of)
 * its contents on each use.
 */
static void
build_dummy_expanded_header(ExpandedRecordHeader *main_erh)
{
    ExpandedRecordHeader *erh;
    TupleDesc   tupdesc = expanded_record_get_tupdesc(main_erh);
 
    /* Ensure we have a short-lived context */
    (void) get_short_term_cxt(main_erh);
 
    /*
     * Allocate dummy header on first time through, or in the unlikely event
     * that the number of fields changes (in which case we just leak the old
     * one).  Include space for its field values in the request.
     */
    erh = main_erh->er_dummy_header;
    if (erh == NULL || erh->nfields != tupdesc->natts)
    {
        char       *chunk;
 
        erh = (ExpandedRecordHeader *)
            MemoryContextAlloc(main_erh->hdr.eoh_context,
                               MAXALIGN(sizeof(ExpandedRecordHeader))
                               + tupdesc->natts * (sizeof(Datum) + sizeof(bool)));
 
        /* Ensure all header fields are initialized to 0/null */
        memset(erh, 0, sizeof(ExpandedRecordHeader));
 
        /*
         * We set up the dummy header with an indication that its memory
         * context is the short-lived context.  This is so that, if any
         * detoasting of out-of-line values happens due to an attempt to
         * extract a composite datum from the dummy header, the detoasted
         * stuff will end up in the short-lived context and not cause a leak.
         * This is cheating a bit on the expanded-object protocol; but since
         * we never pass a R/W pointer to the dummy object to any other code,
         * nothing else is authorized to delete or transfer ownership of the
         * object's context, so it should be safe enough.
         */
        EOH_init_header(&erh->hdr, &ER_methods, main_erh->er_short_term_cxt);
        erh->er_magic = ER_MAGIC;
 
        /* Set up dvalues/dnulls, with no valid contents as yet */
        chunk = (char *) erh + MAXALIGN(sizeof(ExpandedRecordHeader));
        erh->dvalues = (Datum *) chunk;
        erh->dnulls = (bool *) (chunk + tupdesc->natts * sizeof(Datum));
        erh->nfields = tupdesc->natts;
 
        /*
         * The fields we just set are assumed to remain constant through
         * multiple uses of the dummy header to check domain constraints.  All
         * other dummy header fields should be explicitly reset below, to
         * ensure there's not accidental effects of one check on the next one.
         */
 
        main_erh->er_dummy_header = erh;
    }
 
    /*
     * If anything inquires about the dummy header's declared type, it should
     * report the composite base type, not the domain type (since the VALUE in
     * a domain check constraint is of the base type not the domain).  Hence
     * we do not transfer over the IS_DOMAIN flag, nor indeed any of the main
     * header's flags, since the dummy header is empty of data at this point.
     * But don't forget to mark header as dummy.
     */
    erh->flags = ER_FLAG_IS_DUMMY;
 
    /* Copy composite-type identification info */
    erh->er_decltypeid = erh->er_typeid = main_erh->er_typeid;
    erh->er_typmod = main_erh->er_typmod;
 
    /* Dummy header does not need its own tupdesc refcount */
    erh->er_tupdesc = tupdesc;
    erh->er_tupdesc_id = main_erh->er_tupdesc_id;
 
    /*
     * It's tempting to copy over whatever we know about the flat size, but
     * there's no point since we're surely about to modify the dummy record's
     * field(s).  Instead just clear anything left over from a previous usage
     * cycle.
     */
    erh->flat_size = 0;
 
    /* Copy over fvalue if we have it, so that system columns are available */
    erh->fvalue = main_erh->fvalue;
    erh->fstartptr = main_erh->fstartptr;
    erh->fendptr = main_erh->fendptr;
}
 
/*
 * Precheck domain constraints for a set_field operation
 */
static pg_noinline void
check_domain_for_new_field(ExpandedRecordHeader *erh, int fnumber,
                           Datum newValue, bool isnull)
{
    ExpandedRecordHeader *dummy_erh;
    MemoryContext oldcxt;
 
    /* Construct dummy header to contain proposed new field set */
    build_dummy_expanded_header(erh);
    dummy_erh = erh->er_dummy_header;
 
    /*
     * If record isn't empty, just deconstruct it (if needed) and copy over
     * the existing field values.  If it is empty, just fill fields with nulls
     * manually --- don't call deconstruct_expanded_record prematurely.
     */
    if (!ExpandedRecordIsEmpty(erh))
    {
        deconstruct_expanded_record(erh);
        memcpy(dummy_erh->dvalues, erh->dvalues,
               dummy_erh->nfields * sizeof(Datum));
        memcpy(dummy_erh->dnulls, erh->dnulls,
               dummy_erh->nfields * sizeof(bool));
        /* There might be some external values in there... */
        dummy_erh->flags |= erh->flags & ER_FLAG_HAVE_EXTERNAL;
    }
    else
    {
        memset(dummy_erh->dvalues, 0, dummy_erh->nfields * sizeof(Datum));
        memset(dummy_erh->dnulls, true, dummy_erh->nfields * sizeof(bool));
    }
 
    /* Either way, we now have valid dvalues */
    dummy_erh->flags |= ER_FLAG_DVALUES_VALID;
 
    /* Caller error if fnumber is system column or nonexistent column */
    if (unlikely(fnumber <= 0 || fnumber > dummy_erh->nfields))
        elog(ERROR, "cannot assign to field %d of expanded record", fnumber);
 
    /* Insert proposed new value into dummy field array */
    dummy_erh->dvalues[fnumber - 1] = newValue;
    dummy_erh->dnulls[fnumber - 1] = isnull;
 
    /*
     * The proposed new value might be external, in which case we'd better set
     * the flag for that in dummy_erh.  (This matters in case something in the
     * domain check expressions tries to extract a flat value from the dummy
     * header.)
     */
    if (!isnull)
    {
        CompactAttribute *attr = TupleDescCompactAttr(erh->er_tupdesc, fnumber - 1);
 
        if (!attr->attbyval && attr->attlen == -1 &&
            VARATT_IS_EXTERNAL(DatumGetPointer(newValue)))
            dummy_erh->flags |= ER_FLAG_HAVE_EXTERNAL;
    }
 
    /*
     * We call domain_check in the short-lived context, so that any cruft
     * leaked by expression evaluation can be reclaimed.
     */
    oldcxt = MemoryContextSwitchTo(erh->er_short_term_cxt);
 
    /*
     * And now we can apply the check.  Note we use main header's domain cache
     * space, so that caching carries across repeated uses.
     */
    domain_check(ExpandedRecordGetRODatum(dummy_erh), false,
                 erh->er_decltypeid,
                 &erh->er_domaininfo,
                 erh->hdr.eoh_context);
 
    MemoryContextSwitchTo(oldcxt);
 
    /* We might as well clean up cruft immediately. */
    MemoryContextReset(erh->er_short_term_cxt);
}
 
/*
 * Precheck domain constraints for a set_tuple operation
 */
static pg_noinline void
check_domain_for_new_tuple(ExpandedRecordHeader *erh, HeapTuple tuple)
{
    ExpandedRecordHeader *dummy_erh;
    MemoryContext oldcxt;
 
    /* If we're being told to set record to empty, just see if NULL is OK */
    if (tuple == NULL)
    {
        /* We run domain_check in a short-lived context to limit cruft */
        oldcxt = MemoryContextSwitchTo(get_short_term_cxt(erh));
 
        domain_check((Datum) 0, true,
                     erh->er_decltypeid,
                     &erh->er_domaininfo,
                     erh->hdr.eoh_context);
 
        MemoryContextSwitchTo(oldcxt);
 
        /* We might as well clean up cruft immediately. */
        MemoryContextReset(erh->er_short_term_cxt);
 
        return;
    }
 
    /* Construct dummy header to contain replacement tuple */
    build_dummy_expanded_header(erh);
    dummy_erh = erh->er_dummy_header;
 
    /* Insert tuple, but don't bother to deconstruct its fields for now */
    dummy_erh->fvalue = tuple;
    dummy_erh->fstartptr = (char *) tuple->t_data;
    dummy_erh->fendptr = ((char *) tuple->t_data) + tuple->t_len;
    dummy_erh->flags |= ER_FLAG_FVALUE_VALID;
 
    /* Remember if we have any out-of-line field values */
    if (HeapTupleHasExternal(tuple))
        dummy_erh->flags |= ER_FLAG_HAVE_EXTERNAL;
 
    /*
     * We call domain_check in the short-lived context, so that any cruft
     * leaked by expression evaluation can be reclaimed.
     */
    oldcxt = MemoryContextSwitchTo(erh->er_short_term_cxt);
 
    /*
     * And now we can apply the check.  Note we use main header's domain cache
     * space, so that caching carries across repeated uses.
     */
    domain_check(ExpandedRecordGetRODatum(dummy_erh), false,
                 erh->er_decltypeid,
                 &erh->er_domaininfo,
                 erh->hdr.eoh_context);
 
    MemoryContextSwitchTo(oldcxt);
 
    /* We might as well clean up cruft immediately. */
    MemoryContextReset(erh->er_short_term_cxt);
}