Open yacchi opened 10 months ago
Hi @yacchi,
This seems like a reasonable request. We will likely work on this when we re-implement Downloader.
For now we cannot prioritize this, but I will add this to our backlog.
Thanks! Ran~
To @yacchi or anyone else who may be watching this issue --
I haven't tested this, but I believe you can achieve "sequential" I/O by setting download concurrency to 1, which is spec'd to guarantee sequential in-order multipart downloads. If that's the case your WriterAt
effectively becomes safe to write to any sequential I/O implementation.
// sequentialWriterAt adapts WriteAt() calls to a sequential I/O implementation
type sequentialWriterAt struct {
w io.Writer // or copy to another reader, etc.
off int
}
func (v *sequentialWriterAt) WriteAt(p []byte, off int64) (int, error) {
if off != v.off {
return 0, fmt.Errorf("broken write sequence")
}
n, err := v.w.Write(p)
if err != nil {
return n, fmt.Errorf("write: %v", err)
}
v.off += n
return n, nil
}
This is definitely something we'd like to support for concurrent downloads, though.
@lucix-aws
Thanks for the helpful code. It looks like I can certainly do sequentialization that way.
However, if you don't want concurrency, I think the standard GetObject
method is easier because it provides the io.Reader
interface.
I implemented the io.Reader
interface, which allows concurrency, to solve the following problem.
By using the implemented code, it is possible to download the tar file at an average speed of 800MiB/s or more in an environment with sufficient memory.
@lucix-aws @RanVaknin I opened a PR for a concurrent io.Reader/io.WriteCloser for this issue. See #2622
Describe the feature
Currently, the Download function implemented in the Transfer Managers Downloader accepts
io.WriteAt
. Due to this, after writing to a file or buffer, there is a need to create anio.Reader
.Frequently when working with files in Go, the
io.Reader
interface is commonly required. I believe that if the Downloader could directly produce anio.Reader
, it would significantly improve usability.Use Case
Decompressing archive files (e.g., tar, zip) stored in S3
io.Reader
interface. With this feature, it would be possible to directly load and decompress files from S3.Stream processing large files in environments with limited memory or storage
io.Reader
to process streams directly, it becomes possible to handle large files without using storage and with minimal memory consumption.Proposed Solution
The behavior of the AWS CLI's cp command closely aligns with my expectations. For instance, it can be used as follows:
Internally, it appears to use the heap to sequentially output chunks from the beginning. I've created code in my repository that operates in a similar manner using the current Downloader.
https://github.com/yacchi/s3-fast-reader
Other Information
No response
Acknowledgements
AWS Go SDK V2 Module Versions Used
github.com/aws/aws-sdk-go-v2 v1.20.1 github.com/aws/aws-sdk-go-v2/config v1.18.33 github.com/aws/aws-sdk-go-v2/feature/s3/manager v1.11.77 github.com/aws/aws-sdk-go-v2/service/s3 v1.38.2
Go version used
1.20.4