Checking if an error is retryable?

yields · November 29, 2018, 5:48am

Hey all,

Is there a way to check if an error coming from .Transact() or .ReadTransact() is retryable in golang?

I’ve found some error predicates[1], but i’m confused by the docs there, how does it return “true”?
I thought the docs imply I should compare it to err.Code, but I can’t find any 5000 error code at all[1].

ajbeamon · November 29, 2018, 8:25pm

The error predicate constants are for use with fdb_error_predicate in the C API. Some bindings expose APIs to use this function, but the Go bindings do not currently.

The best way to check for retryability right now is using OnError. If the error is retryable, the returned future will be set normally. If it isn’t, then the future will be set with the error that is passed in to it.

It should be noted that this function will reset your transaction and possibly inject a delay for backoff purposes.

If you wanted to see which errors are considered retryable, you can look at the implementation of fdb_error_predicate:

github.com

ajbeamon/foundationdb/blob/d46231580939e4acd7a802ee0ecc77c8875e4b46/bindings/c/fdb_c.cpp#L65




#define TSAV_ERROR(type, error) ((FDBFuture*)(ThreadFuture<type>(error())).extractPtr())




extern "C" DLLEXPORT
const char *fdb_get_error( fdb_error_t code ) {
	return Error::fromUnvalidatedCode( code ).what();
}


extern "C" DLLEXPORT
fdb_bool_t fdb_error_predicate( int predicate_test, fdb_error_t code ) {
	if(predicate_test == FDBErrorPredicates::RETRYABLE) {
		return fdb_error_predicate( FDBErrorPredicates::MAYBE_COMMITTED, code ) ||
				fdb_error_predicate( FDBErrorPredicates::RETRYABLE_NOT_COMMITTED, code );
	}
	if(predicate_test == FDBErrorPredicates::MAYBE_COMMITTED) {
		return code == error_code_commit_unknown_result ||
				code == error_code_cluster_version_changed;
	}
	if(predicate_test == FDBErrorPredicates::RETRYABLE_NOT_COMMITTED) {
		return code == error_code_not_committed ||

And also the mapping of error names to codes:

github.com

ajbeamon/foundationdb/blob/master/flow/error_definitions.h

/*
 * error_definitions.h
 *
 * This source file is part of the FoundationDB open source project
 *
 * Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

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