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error decoding response body
after upgrade to object store 0.10
#5882
Comments
error decoding response body
after upgrade to object store 0.10
I think we would need a reproducer to action this, the linked issues aren't even clearly implicating object_store |
Please also print the source of the error via |
@thomasfrederikhoeck @k-ye can you guys provide additional details please |
@Xuanwo I would love to be of more help but I don't now how to do this in delta-rs (an in turn object_store). I didn't help setting the timeout to 300s. @ion-elgreco Can you point me in the direction of how I can provide better logs? |
Hi, if you can consistently reproduce this issue, please change the following places: fn object_store_to_py(err: ObjectStoreError) -> PyErr {
match err {
ObjectStoreError::NotFound { .. } => PyFileNotFoundError::new_err(err.to_string()),
ObjectStoreError::Generic { source, .. }
if source.to_string().contains("AWS_S3_ALLOW_UNSAFE_RENAME") =>
{
DeltaProtocolError::new_err(source.to_string())
}
_ => PyIOError::new_err(err.to_string()),
}
} Don't use |
@Xuanwo Ah thanks!! I get the following consistently :
I also tried bumping the timeout to
|
I suspect there's an issue with the network connection between your environment and Azure. Could you provide more details about your setup?
|
@Xuanwo I might be network related but I have some feeling that is related to how
The benchmark took 1+ hours with no failure while the delta-rs call fails within a few minutes. |
@Xuanwo @tustvold I can concur this also happens to us in v0.18.1/2, I can see logs in LakeFS which says "context canceled". Somewhere in object store the connection is getting dropped constantly with large files. Can you guys give suggestions on how to debug. For me I am connecting within a VNET in EU amsterdam |
Are you mixing IO with CPU bound work, I wonder if you are stalling out the tokio runtime |
Hmm I am not sure, I started working on delta-rs a year ago and most of this FileSystem handling code was already there. We essentially create a DeltaFileSystemHandler which we expose to Python. In python we create a DeltaStorageHandler which inherits the pyarrow FileSystemHandler methods, which we implement to call the Rust DeltaFileSystemHandler. I think Pyarrow just calls read on an ObjectInputFile, which in rust calls
Here |
That at least looks plausible, how big are the ranges we're fetching and how long are we fetching for? I wonder if we're running into some Azure limit, it sounds like they're hanging up for some reason |
What do you mean with looks plausible? :) @tustvold I'll put some print statements in the ranges, to see what is being requested! Will get back to you on that! |
I can't see anything obviously wrong, but also don't know much about pyarrow so can't say definitively if it is correct |
@tustvold It seems pyarrow fetches 4 files in parallel and then reads around 30MB each time: https://gist.github.com/ion-elgreco/e2339990843755b40475dbd6e72e4697 |
That's on the chonkier end of optimal, but not ludicrous. How long do the fetches take? |
Hmm what would you suggest is more optimal? Like 10MB? So now my VPN connection throughput is working fine, so it seems each fetch takes around 4-8 secs. python/src/filesystem.rs:501:17] elapsed.as_secs() = 6
[python/src/filesystem.rs:473:9] (&self.path, &nbytes) = (
Path {
raw: "product_line_code=DUMMY/100-f1cafe66-476f-4818-8199-5c5a4a6eb4ef-0.parquet",
},
Some(
33231426,
),
) |
Oh... This is almost certainly what is causing this issue, very few VPNs will support large volume data transfer. It is almost certainly dropping the connections in the interest of preserving QoS for other users. Shuttling data through a VPN box is not only likely to be the cause of your issue, it is also likely very expensive. |
I see that could explain it for me, however my colleague saw timeouts on his Azure Compute instance, so Azure <-> Azure connection within our vnet |
I'm afraid I don't have any other ideas, something outside of object_store is dropping the connection. This could be Azure itself, Azure blob storage definitely gives off the impression of being an MVP that somehow got shipped, but it is more likely to be some middleware network appliance, like a VPN, NAT gateway or similar. AWS has private gateway endpoints that must be configured for S3, I am not sure if Azure needs something similar. |
@tustvold The weird thing is that I can run some rather large data opeartions (taking an 1+ hour) with I can maybe add: Before this PR in polars we sometimes saw similar issues but I'm very far from knowledge-able on networking. |
This is why I asked about starving the tokio threadpool, this does not appear to be the issue @ion-elgreco is running into from what he has shared.
Azcopy will be using multipart uploads, which uses smaller requests that are therefore less susceptible to dropped connections |
I got a bit confused myself here, but @thomasfrederikhoeck you have issues during Optimize where the data is being read differently. @tustvold, here it seems we read a Parquet object within a tokio task, should this be rayon threadpool instead? let stream = match operations {
OptimizeOperations::Compact(bins) => futures::stream::iter(bins)
.flat_map(|(_, (partition, bins))| {
futures::stream::iter(bins).map(move |bin| (partition.clone(), bin))
})
.map(|(partition, files)| {
debug!(
"merging a group of {} files in partition {:?}",
files.len(),
partition,
);
for file in files.iter() {
debug!(" file {}", file.location);
}
let object_store_ref = log_store.object_store();
let batch_stream = futures::stream::iter(files.clone())
.then(move |file| {
let object_store_ref = object_store_ref.clone();
async move {
let file_reader = ParquetObjectReader::new(object_store_ref, file);
ParquetRecordBatchStreamBuilder::new(file_reader)
.await?
.build()
}
})
.try_flatten()
.boxed();
let rewrite_result = tokio::task::spawn(Self::rewrite_files(
self.task_parameters.clone(),
partition,
files,
log_store.object_store().clone(),
futures::future::ready(Ok(batch_stream)),
));
util::flatten_join_error(rewrite_result)
})
.boxed(), Later down in the code we read that stream from above one by one and cast each recordBatch which is cpu bound I guess? And then we write it as a parquet again: while let Some(maybe_batch) = read_stream.next().await {
let mut batch = maybe_batch?;
batch = super::cast::cast_record_batch(
&batch,
task_parameters.file_schema.clone(),
false,
true,
)?;
partial_metrics.num_batches += 1;
writer.write(&batch).await.map_err(DeltaTableError::from)?;
} |
You should avoid doing any non-trivial CPU-bound work on the tokio threadpool that you use for IO. The way I've seen this done successfully is running DF in one tokio threadpool, and then spawning IO from it into a different one. There was some work in the past to make this easier, see #4040, but I never got it over the line. I'll file a ticket Edit: Filed #6248 |
I think the challenge for DataFusion is that almost all of its processing is CPU bound, so it makes more sense to move it wholesale to its own threadpool. Calling spawn_blocking for every CPU-bound section would not only be extremely verbose, but would have terrible performance as the per-task overhead for spawn_blocking is very high. Ultimately the decision was made to make DataFusion exection async, some might weigh the tradeoffs involved differently and argue this is unfortunate, but whatever the case this means DataFusion needs to run in an async-scheduler. This could be tokio, or something else, but tokio is the default choice. You may be interested to look into apache/datafusion#2199 where I tried to move DF away from async/tokio, but it was an extremely complicated project back then, and is likely even less practical now. If this is something of interest I would recommend filing a ticket in DataFusion. I am loathe to, as I do not have the time or capacity to drive such an initiative myself, but I personally think it would be valuable. |
If I understand correctly the point is that we don't want to move CPU work somewhere because that's happening in too many places to keep track. Instead we want to "special case" the IO work and move that around. Is that right? |
This is what we do at InfluxData and it works reasonably well. You have to be slightly careful so that you don't miss some IO calls or that you don't hand IO handles (e.g. sockets, or HTTP connections wrapping them) from the IO runtime to the CPU runtime. But other than that, it works and improves both our end2end latency and the tokio internal metrics. |
If we did this I think it is important to do performance tests -- by default tokio potentially uses many (100s I think?) of threads for this blocking thread pool and if we are not careful launching CPU bound work on them will mean the threads are over subscribed (more threads than CPUs) which will reduce effectiveness
It would be really helpful to document / write a blog about how this works -- I think it would be widely read and appreciated. @ion-elgreco any interest / chance that you or someone else in the delta lake team would be able to? I would be happy to collaborate. |
Just experienced this issue as well. This is an Azure VM accessing Azure blob storage. Happens intermittently. We have 60 tasks running in parallel and happens ocassionally and retrying resolves it. We set the pyarrow io thread count to 2 and cpu thread count to 1 on a machine with 120 vCPUs. |
I've created apache/datafusion#12393 to track this on DataFusion's end. I am also going to close this issue, as I don't believe there is any work planned in this repository related to this, ultimately the issue lies in how DataFusion and its consumers are wiring up IO. |
Why is this being closed? We are experiencing this bug on pyarrow/arrow-rs without Datafusion. |
delta-rs makes use of DataFusion, and as discussed in #5882 (comment). I am closing this issue to make it clear that no work is planned in this repository related to this |
I see. Even though the trace points to pyarrow? I was under the impression that when reading the table itself, delta-rs is no longer in the middle:
Should I repost this on the datafusion issue or do you think this is different and is related to pyarrow/arrow-rs |
@alamb what's the question exactly? Currently our logstore is spawning all tasks in a separate runtime that can be configured |
The issue pertains to how CPU bound work is starving IO, this side-channel will not be reflected in stack traces. Additionally there is something in-between that is connecting pyarrow to object_store, we don't provide such an integration. The delta-rs people will likely be best placed to comment on what this is. |
Let's leave this ticket open until we sort out the next steps (though I agree with @tustvold that I don't predict any code changes in arrow-rs) |
My question is "would you be willing to summarize this ticket / write up a blog post (perhaps on the DataFusion blog) explaining how to spawn IO related tasks on a different thread pool? I am 🎣 for help as I would like to write this blog too (so we can distill down this ticket and others for future discussion) but I am struggling to find time |
I think there's something else going on that is independent of the tokio runtime issues. I was able to reproduce this locally with a somewhat broken So I think we should extend the retry logic to capture this case. However this might be difficult in the streaming case (i.e. when the error occurs mid-stream), see arrow-rs/object_store/src/client/get.rs Lines 245 to 251 in 7a5155c
At least we should try to improve the error message. It seems that the |
Retrying interrupted streaming requests is tracked by - #6287 I'm a bit wary of this ticket just becoming a general dumping ground for any networking related issue, which is part of why I closed it... |
Error display improvements tracked by #6377. |
Ok so here is my summary of this ticket, and the action items going forward. Problem The Causes There are two related causes of this:
Outcome As for the follow on work:
Please let me know if I have missed anything, otherwise I will look to close this issue in favour of the linked issues in the next few days. I think this issue has been very helpful, and I'm grateful for everyone who has participated, but I am keen to put this on a more actionable footing. |
I could but not soon, I recently started a new job so that's keeping me quite busy |
What I still don't quite get is that we are still seeing errors but only on the reading side through the DeltaFileHandler which is exposed into a pyarrow filesystem, there should be zero cpu bound tasks on that tokio runtime |
Perhaps it is related to just some networks errors and a retry of streaming and #6287 tracks retrying interrupted streaming requests |
@alamb delta-io/delta-rs#2595 (comment) I asked them to add a timeout increase and that resolved it, i guess it would already help a lot if the true error surfaces, it might be all those folks have low network throughput |
I believe @itsjunetime may be able to take a look at improving the errors and retries. We'll keep the tickets updated |
I've opened a PR #6519 that will retry on |
Describe the bug
We bumped the object store to 0.10 in delta-rs, and now we already seeing a couple reports on the following error
error decoding response body
. Happens on Azure and S3.See delta-io/delta-rs#2595 and delta-io/delta-rs#2592
To Reproduce
Seems to occur when reading tables or doing operations on them.
Expected behavior
Don't have an issue decoding the response body
Additional context
@thomasfrederikhoeck @k-ye
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