CODEWITHSUNDEEP
amazon-web-servicess3cmd
Matt Vukas
Matt Vukas

Reputation: 3295

Is there any way to specify a max number of retries when using s3cmd?

I've looked through the usage guide as well as the config docs and I'm just not seeing it. This is the output for my bash script that uses s3cmd sync when S3 appeared to be down:

WARNING: Retrying failed request: /some/bucket/path/
WARNING: 503 (Service Unavailable): 
WARNING: Waiting 3 sec...
WARNING: Retrying failed request: /some/bucket/path/
WARNING: 503 (Service Unavailable): 
WARNING: Waiting 6 sec...
ERROR: The read operation timed out

It looks like it is retrying twice using exponential backoffs, then failing. Surely there must be some way to explicitly state how many times s3cmd should retry a failed network call?

Upvotes: 0

Views: 2719

Answers (2)

Volkan Paksoy
Volkan Paksoy

Reputation: 6957

I don't think you can the set the maximum retry count. I had a look at its source code on GitHub (https://github.com/s3tools/s3cmd/blob/master/S3/S3.py).

Looks like that value is 5 and hard-coded:

Line 240:

## Maximum attempts of re-issuing failed requests
_max_retries = 5

And the retry interval is calculated as:

Line 1004:

def _fail_wait(self, retries):
    # Wait a few seconds. The more it fails the more we wait.
    return (self._max_retries - retries + 1) * 3

and the actual code that carries out the retries:

if response["status"] >= 500:
        e = S3Error(response)

        if response["status"] == 501:
            ## NotImplemented server error - no need to retry
            retries = 0

        if retries:
            warning(u"Retrying failed request: %s" % resource['uri'])
            warning(unicode(e))
            warning("Waiting %d sec..." % self._fail_wait(retries))
            time.sleep(self._fail_wait(retries))
            return self.send_request(request, retries - 1)
        else:
            raise e

So I think after the second try some other error occurred and it caused it to get out of the retry loop.

Upvotes: 3

E.J. Brennan
E.J. Brennan

Reputation: 46849

Its very unlikely the 503 is because S3 is down, its almost never, ever 'down'. More likely you account has been throttled because you are making too many requests in too short a period.

You should either slow down your requests, if you control the speed, or I would recommend picking better keys, i.e. keys that don't all start with the same prefix - a nice wide range of keys will allow s3 to spread the workload better.

From Jeff Barr's blog post:

Further, keys in S3 are partitioned by prefix.

As we said, S3 has automation that continually looks for areas of the keyspace that need splitting. Partitions are split either due to sustained high request rates, or because they contain a large number of keys (which would slow down lookups within the partition). There is overhead in moving keys into newly created partitions, but with request rates low and no special tricks, we can keep performance reasonably high even during partition split operations. This split operation happens dozens of times a day all over S3 and simply goes unnoticed from a user performance perspective. However, when request rates significantly increase on a single partition, partition splits become detrimental to request performance. How, then, do these heavier workloads work over time? Smart naming of the keys themselves!

We frequently see new workloads introduced to S3 where content is organized by user ID, or game ID, or other similar semi-meaningless identifier. Often these identifiers are incrementally increasing numbers, or date-time constructs of various types. The unfortunate part of this naming choice where S3 scaling is concerned is two-fold: First, all new content will necessarily end up being owned by a single partition (remember the request rates from above…). Second, all the partitions holding slightly older (and generally less ‘hot’) content get cold much faster than other naming conventions, effectively wasting the available operations per second that each partition can support by making all the old ones cold over time.

The simplest trick that makes these schemes work well in S3 at nearly any request rate is to simply reverse the order of the digits in this identifier (use seconds of precision for date or time-based identifiers). These identifiers then effectively start with a random number – and a few of them at that – which then fans out the transactions across many potential child partitions. Each of those child partitions scales close enough to linearly (even with some content being hotter or colder) that no meaningful operations per second budget is wasted either. In fact, S3 even has an algorithm to detect this parallel type of write pattern and will automatically create multiple child partitions from the same parent simultaneously – increasing the system’s operations per second budget as request heat is detected.

https://aws.amazon.com/blogs/aws/amazon-s3-performance-tips-tricks-seattle-hiring-event/

Upvotes: 0

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