postgres/src/backend/access/table/tableamapi.c

/*----------------------------------------------------------------------
 *
 * 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 we expect to be statically allocated.
 */
const TableAmRoutine *
GetTableAmRoutine(Oid amhandler)
{
	Datum		datum;
	const TableAmRoutine *routine;

	datum = OidFunctionCall0(amhandler);
	routine = (const 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);

	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;
}