flink-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Vishnu Viswanath <vishnu.viswanat...@gmail.com>
Subject Re: Checkpointing with RocksDB as statebackend
Date Tue, 14 Mar 2017 14:31:06 GMT
Hi Stephan,

Is there a ticket number/link to track this, My job has all the conditions
you mentioned.

Thanks,
Vishnu

On Tue, Mar 14, 2017 at 7:13 AM, Stephan Ewen <sewen@apache.org> wrote:

> Hi Vinay!
>
> We just discovered a bug in RocksDB. The bug affects windows without
> reduce() or fold(), windows with evictors, and ListState.
>
> A certain access pattern in RocksDB starts being so slow after a certain
> size-per-key that it basically brings down the streaming program and the
> snapshots.
>
> We are reaching out to the RocksDB folks and looking for workarounds in
> Flink.
>
> Greetings,
> Stephan
>
>
> On Wed, Mar 1, 2017 at 12:10 PM, Stephan Ewen <sewen@apache.org> wrote:
>
>> @vinay  Can you try to not set the buffer timeout at all? I am actually
>> not sure what would be the effect of setting it to a negative value, that
>> can be a cause of problems...
>>
>>
>> On Mon, Feb 27, 2017 at 7:44 PM, Seth Wiesman <swiesman@mediamath.com>
>> wrote:
>>
>>> Vinay,
>>>
>>>
>>>
>>> The bucketing sink performs rename operations during the checkpoint and
>>> if it tries to rename a file that is not yet consistent that would cause a
>>> FileNotFound exception which would fail the checkpoint.
>>>
>>>
>>>
>>> Stephan,
>>>
>>>
>>>
>>> Currently my aws fork contains some very specific assumptions about the
>>> pipeline that will in general only hold for my pipeline. This is because
>>> there were still some open questions that  I had about how to solve
>>> consistency issues in the general case. I will comment on the Jira issue
>>> with more specific.
>>>
>>>
>>>
>>> Seth Wiesman
>>>
>>>
>>>
>>> *From: *vinay patil <vinay18.patil@gmail.com>
>>> *Reply-To: *"user@flink.apache.org" <user@flink.apache.org>
>>> *Date: *Monday, February 27, 2017 at 1:05 PM
>>> *To: *"user@flink.apache.org" <user@flink.apache.org>
>>>
>>> *Subject: *Re: Checkpointing with RocksDB as statebackend
>>>
>>>
>>>
>>> Hi Seth,
>>>
>>> Thank you for your suggestion.
>>>
>>> But if the issue is only related to S3, then why does this happen when I
>>> replace the S3 sink  to HDFS as well (for checkpointing I am using HDFS
>>> only )
>>>
>>> Stephan,
>>>
>>> Another issue I see is when I set env.setBufferTimeout(-1) , and keep
>>> the checkpoint interval to 10minutes, I have observed that nothing gets
>>> written to sink (tried with S3 as well as HDFS), atleast I was expecting
>>> pending files here.
>>>
>>> This issue gets worst when checkpointing is disabled  as nothing is
>>> written.
>>>
>>>
>>>
>>>
>>> Regards,
>>>
>>> Vinay Patil
>>>
>>>
>>>
>>> On Mon, Feb 27, 2017 at 10:55 PM, Stephan Ewen [via Apache Flink User
>>> Mailing List archive.] <[hidden email]> wrote:
>>>
>>> Hi Seth!
>>>
>>>
>>>
>>> Wow, that is an awesome approach.
>>>
>>>
>>>
>>> We have actually seen these issues as well and we are looking to
>>> eventually implement our own S3 file system (and circumvent Hadoop's S3
>>> connector that Flink currently relies on): https://issues.apache.org
>>> /jira/browse/FLINK-5706
>>>
>>>
>>>
>>> Do you think your patch would be a good starting point for that and
>>> would you be willing to share it?
>>>
>>>
>>>
>>> The Amazon AWS SDK for Java is Apache 2 licensed, so that is possible to
>>> fork officially, if necessary...
>>>
>>>
>>>
>>> Greetings,
>>>
>>> Stephan
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> On Mon, Feb 27, 2017 at 5:15 PM, Seth Wiesman <[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11943&i=0>> wrote:
>>>
>>> Just wanted to throw in my 2cts.
>>>
>>>
>>>
>>> I’ve been running pipelines with similar state size using rocksdb which
>>> externalize to S3 and bucket to S3. I was getting stalls like this and
>>> ended up tracing the problem to S3 and the bucketing sink. The solution was
>>> two fold:
>>>
>>>
>>>
>>> 1)       I forked hadoop-aws and have it treat flink as a source of
>>> truth. Emr uses a dynamodb table to determine if S3 is inconsistent.
>>> Instead I say that if flink believes that a file exists on S3 and we don’t
>>> see it then I am going to trust that flink is in a consistent state and S3
>>> is not. In this case, various operations will perform a back off and retry
>>> up to a certain number of times.
>>>
>>>
>>>
>>> 2)       The bucketing sink performs multiple renames over the lifetime
>>> of a file, occurring when a checkpoint starts and then again on
>>> notification after it completes. Due to S3’s consistency guarantees the
>>> second rename of file can never be assured to work and will eventually fail
>>> either during or after a checkpoint. Because there is no upper bound on the
>>> time it will take for a file on S3 to become consistent, retries cannot
>>> solve this specific problem as it could take upwards of many minutes to
>>> rename which would stall the entire pipeline. The only viable solution I
>>> could find was to write a custom sink which understands S3. Each writer
>>> will write file locally and then copy it to S3 on checkpoint. By only
>>> interacting with S3 once per file it can circumvent consistency issues all
>>> together.
>>>
>>>
>>>
>>> Hope this helps,
>>>
>>>
>>>
>>> Seth Wiesman
>>>
>>>
>>>
>>> *From: *vinay patil <[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11943&i=1>>
>>> *Reply-To: *"[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11943&i=2>" <[hidden
email]
>>> <http://user/SendEmail.jtp?type=node&node=11943&i=3>>
>>> *Date: *Saturday, February 25, 2017 at 10:50 AM
>>> *To: *"[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11943&i=4>" <[hidden
email]
>>> <http://user/SendEmail.jtp?type=node&node=11943&i=5>>
>>> *Subject: *Re: Checkpointing with RocksDB as statebackend
>>>
>>>
>>>
>>> HI Stephan,
>>>
>>> Just to avoid the confusion here, I am using S3 sink for writing the
>>> data, and using HDFS for storing checkpoints.
>>>
>>> There are 2 core nodes (HDFS) and two task nodes on EMR
>>>
>>>
>>> I replaced s3 sink with HDFS for writing data in my last test.
>>>
>>> Let's say the checkpoint interval is 5 minutes, now within 5minutes of
>>> run the state size grows to 30GB ,  after checkpointing the 30GB state that
>>> is maintained in rocksDB has to be copied to HDFS, right ?  is this causing
>>> the pipeline to stall ?
>>>
>>>
>>> Regards,
>>>
>>> Vinay Patil
>>>
>>>
>>>
>>> On Sat, Feb 25, 2017 at 12:22 AM, Vinay Patil <[hidden email]> wrote:
>>>
>>> Hi Stephan,
>>>
>>> To verify if S3 is making teh pipeline stall, I have replaced the S3
>>> sink with HDFS and kept minimum pause between checkpoints to 5minutes,
>>> still I see the same issue with checkpoints getting failed.
>>>
>>> If I keep the  pause time to 20 seconds, all checkpoints are completed ,
>>> however there is a hit in overall throughput.
>>>
>>>
>>>
>>>
>>> Regards,
>>>
>>> Vinay Patil
>>>
>>>
>>>
>>> On Fri, Feb 24, 2017 at 10:09 PM, Stephan Ewen [via Apache Flink User
>>> Mailing List archive.] <[hidden email]> wrote:
>>>
>>> Flink's state backends currently do a good number of "make sure this
>>> exists" operations on the file systems. Through Hadoop's S3 filesystem,
>>> that translates to S3 bucket list operations, where there is a limit in how
>>> many operation may happen per time interval. After that, S3 blocks.
>>>
>>>
>>>
>>> It seems that operations that are totally cheap on HDFS are hellishly
>>> expensive (and limited) on S3. It may be that you are affected by that.
>>>
>>>
>>>
>>> We are gradually trying to improve the behavior there and be more S3
>>> aware.
>>>
>>>
>>>
>>> Both 1.3-SNAPSHOT and 1.2-SNAPSHOT already contain improvements there.
>>>
>>>
>>>
>>> Best,
>>>
>>> Stephan
>>>
>>>
>>>
>>>
>>>
>>> On Fri, Feb 24, 2017 at 4:42 PM, vinay patil <[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11891&i=0>> wrote:
>>>
>>> Hi Stephan,
>>>
>>> So do you mean that S3 is causing the stall , as I have mentioned in my
>>> previous mail, I could not see any progress for 16minutes as checkpoints
>>> were getting failed continuously.
>>>
>>>
>>>
>>> On Feb 24, 2017 8:30 PM, "Stephan Ewen [via Apache Flink User Mailing
>>> List archive.]" <[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11887&i=0>> wrote:
>>>
>>> Hi Vinay!
>>>
>>>
>>>
>>> True, the operator state (like Kafka) is currently not asynchronously
>>> checkpointed.
>>>
>>>
>>>
>>> While it is rather small state, we have seen before that on S3 it can
>>> cause trouble, because S3 frequently stalls uploads of even data amounts as
>>> low as kilobytes due to its throttling policies.
>>>
>>>
>>>
>>> That would be a super important fix to add!
>>>
>>>
>>>
>>> Best,
>>>
>>> Stephan
>>>
>>>
>>>
>>>
>>>
>>> On Fri, Feb 24, 2017 at 2:58 PM, vinay patil <[hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11885&i=0>> wrote:
>>>
>>> Hi,
>>>
>>> I have attached a snapshot for reference:
>>> As you can see all the 3 checkpointins failed , for checkpoint ID 2 and
>>> 3 it
>>> is stuck at the Kafka source after 50%
>>> (The data sent till now by Kafka source 1 is 65GB and sent by source 2 is
>>> 15GB )
>>>
>>> Within 10minutes 15M records were processed, and for the next 16minutes
>>> the
>>> pipeline is stuck , I don't see any progress beyond 15M because of
>>> checkpoints getting failed consistently.
>>>
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.na
>>> bble.com/file/n11882/Checkpointing_Failed.png>
>>>
>>>
>>>
>>> --
>>> View this message in context: http://apache-flink-user-maili
>>> ng-list-archive.2336050.n4.nabble.com/Re-Checkpointing-with-
>>> RocksDB-as-statebackend-tp11752p11882.html
>>>
>>> Sent from the Apache Flink User Mailing List archive. mailing list
>>> archive at Nabble.com.
>>>
>>>
>>>
>>>
>>> ------------------------------
>>>
>>> *If you reply to this email, your message will be added to the
>>> discussion below:*
>>>
>>> http://apache-flink-user-mailing-list-archive.2336050.n4.nab
>>> ble.com/Re-Checkpointing-with-RocksDB-as-statebackend-tp11752p11885.html
>>>
>>> To start a new topic under Apache Flink User Mailing List archive.,
>>> email [hidden email]
>>> <http://user/SendEmail.jtp?type=node&node=11887&i=1>
>>> To unsubscribe from Apache Flink User Mailing List archive., click here.
>>> NAML
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/template/NamlServlet.jtp?macro=macro_viewer&id=instant_html%21nabble%3Aemail.naml&base=nabble.naml.namespaces.BasicNamespace-nabble.view.web.template.NabbleNamespace-nabble.view.web.template.NodeNamespace&breadcrumbs=notify_subscribers%21nabble%3Aemail.naml-instant_emails%21nabble%3Aemail.naml-send_instant_email%21nabble%3Aemail.naml>
>>>
>>>
>>> ------------------------------
>>>
>>> View this message in context: Re: Checkpointing with RocksDB as
>>> statebackend
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Re-Checkpointing-with-RocksDB-as-statebackend-tp11752p11887.html>
>>>
>>> Sent from the Apache Flink User Mailing List archive. mailing list
>>> archive
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/>
>>> at Nabble.com.
>>>
>>>
>>>
>>>
>>> ------------------------------
>>>
>>> *If you reply to this email, your message will be added to the
>>> discussion below:*
>>>
>>> http://apache-flink-user-mailing-list-archive.2336050.n4.nab
>>> ble.com/Re-Checkpointing-with-RocksDB-as-statebackend-tp11752p11891.html
>>>
>>> To start a new topic under Apache Flink User Mailing List archive.,
>>> email [hidden email]
>>> To unsubscribe from Apache Flink User Mailing List archive., click here.
>>> NAML
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/template/NamlServlet.jtp?macro=macro_viewer&id=instant_html%21nabble%3Aemail.naml&base=nabble.naml.namespaces.BasicNamespace-nabble.view.web.template.NabbleNamespace-nabble.view.web.template.NodeNamespace&breadcrumbs=notify_subscribers%21nabble%3Aemail.naml-instant_emails%21nabble%3Aemail.naml-send_instant_email%21nabble%3Aemail.naml>
>>>
>>>
>>>
>>>
>>>
>>>
>>> ------------------------------
>>>
>>> View this message in context: Re: Checkpointing with RocksDB as
>>> statebackend
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Re-Checkpointing-with-RocksDB-as-statebackend-tp11752p11913.html>
>>> Sent from the Apache Flink User Mailing List archive. mailing list
>>> archive
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/>
>>> at Nabble.com.
>>>
>>>
>>>
>>>
>>> ------------------------------
>>>
>>> *If you reply to this email, your message will be added to the
>>> discussion below:*
>>>
>>> http://apache-flink-user-mailing-list-archive.2336050.n4.nab
>>> ble.com/Re-Checkpointing-with-RocksDB-as-statebackend-tp11752p11943.html
>>>
>>> To start a new topic under Apache Flink User Mailing List archive.,
>>> email [hidden email]
>>> To unsubscribe from Apache Flink User Mailing List archive., click here.
>>> NAML
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/template/NamlServlet.jtp?macro=macro_viewer&id=instant_html%21nabble%3Aemail.naml&base=nabble.naml.namespaces.BasicNamespace-nabble.view.web.template.NabbleNamespace-nabble.view.web.template.NodeNamespace&breadcrumbs=notify_subscribers%21nabble%3Aemail.naml-instant_emails%21nabble%3Aemail.naml-send_instant_email%21nabble%3Aemail.naml>
>>>
>>>
>>>
>>>
>>> ------------------------------
>>>
>>> View this message in context: Re: Checkpointing with RocksDB as
>>> statebackend
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Re-Checkpointing-with-RocksDB-as-statebackend-tp11752p11949.html>
>>> Sent from the Apache Flink User Mailing List archive. mailing list
>>> archive
>>> <http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/>
>>> at Nabble.com.
>>>
>>>
>>
>

Mime
View raw message