tableamapi.c

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/*----------------------------------------------------------------------
 *
 * tableamapi.c
 *      Support routines for API for Postgres table access methods
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/backend/access/table/tableamapi.c
 *----------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "access/tableam.h"
#include "access/xact.h"
#include "commands/defrem.h"
#include "miscadmin.h"
#include "utils/guc_hooks.h"
 
 
/*
 * GetTableAmRoutine
 *      Call the specified access method handler routine to get its
 *      TableAmRoutine struct, which will be palloc'd in the caller's
 *      memory context.
 */
const TableAmRoutine *
GetTableAmRoutine(Oid amhandler)
{
    Datum       datum;
    const TableAmRoutine *routine;
 
    datum = OidFunctionCall0(amhandler);
    routine = (TableAmRoutine *) DatumGetPointer(datum);
 
    if (routine == NULL || !IsA(routine, TableAmRoutine))
        elog(ERROR, "table access method handler %u did not return a TableAmRoutine struct",
             amhandler);
 
    /*
     * Assert that all required callbacks are present. That makes it a bit
     * easier to keep AMs up to date, e.g. when forward porting them to a new
     * major version.
     */
    Assert(routine->scan_begin != NULL);
    Assert(routine->scan_end != NULL);
    Assert(routine->scan_rescan != NULL);
    Assert(routine->scan_getnextslot != NULL);
 
    Assert(routine->parallelscan_estimate != NULL);
    Assert(routine->parallelscan_initialize != NULL);
    Assert(routine->parallelscan_reinitialize != NULL);
 
    Assert(routine->index_fetch_begin != NULL);
    Assert(routine->index_fetch_reset != NULL);
    Assert(routine->index_fetch_end != NULL);
    Assert(routine->index_fetch_tuple != NULL);
 
    Assert(routine->tuple_fetch_row_version != NULL);
    Assert(routine->tuple_tid_valid != NULL);
    Assert(routine->tuple_get_latest_tid != NULL);
    Assert(routine->tuple_satisfies_snapshot != NULL);
    Assert(routine->index_delete_tuples != NULL);
 
    Assert(routine->tuple_insert != NULL);
 
    /*
     * Could be made optional, but would require throwing error during
     * parse-analysis.
     */
    Assert(routine->tuple_insert_speculative != NULL);
    Assert(routine->tuple_complete_speculative != NULL);
 
    Assert(routine->multi_insert != NULL);
    Assert(routine->tuple_delete != NULL);
    Assert(routine->tuple_update != NULL);
    Assert(routine->tuple_lock != NULL);
 
    Assert(routine->relation_set_new_filelocator != NULL);
    Assert(routine->relation_nontransactional_truncate != NULL);
    Assert(routine->relation_copy_data != NULL);
    Assert(routine->relation_copy_for_cluster != NULL);
    Assert(routine->relation_vacuum != NULL);
    Assert(routine->scan_analyze_next_block != NULL);
    Assert(routine->scan_analyze_next_tuple != NULL);
    Assert(routine->index_build_range_scan != NULL);
    Assert(routine->index_validate_scan != NULL);
 
    Assert(routine->relation_size != NULL);
    Assert(routine->relation_needs_toast_table != NULL);
 
    Assert(routine->relation_estimate_size != NULL);
 
    /* optional, but one callback implies presence of the other */
    Assert((routine->scan_bitmap_next_block == NULL) ==
           (routine->scan_bitmap_next_tuple == NULL));
    Assert(routine->scan_sample_next_block != NULL);
    Assert(routine->scan_sample_next_tuple != NULL);
 
    return routine;
}
 
/* check_hook: validate new default_table_access_method */
bool
check_default_table_access_method(char **newval, void **extra, GucSource source)
{
    if (**newval == '\0')
    {
        GUC_check_errdetail("\"%s\" cannot be empty.",
                            "default_table_access_method");
        return false;
    }
 
    if (strlen(*newval) >= NAMEDATALEN)
    {
        GUC_check_errdetail("\"%s\" is too long (maximum %d characters).",
                            "default_table_access_method", NAMEDATALEN - 1);
        return false;
    }
 
    /*
     * If we aren't inside a transaction, or not connected to a database, we
     * cannot do the catalog access necessary to verify the method.  Must
     * accept the value on faith.
     */
    if (IsTransactionState() && MyDatabaseId != InvalidOid)
    {
        if (!OidIsValid(get_table_am_oid(*newval, true)))
        {
            /*
             * When source == PGC_S_TEST, don't throw a hard error for a
             * nonexistent table access method, only a NOTICE. See comments in
             * guc.h.
             */
            if (source == PGC_S_TEST)
            {
                ereport(NOTICE,
                        (errcode(ERRCODE_UNDEFINED_OBJECT),
                         errmsg("table access method \"%s\" does not exist",
                                *newval)));
            }
            else
            {
                GUC_check_errdetail("Table access method \"%s\" does not exist.",
                                    *newval);
                return false;
            }
        }
    }
 
    return true;
}