Pithos - Architecture and .NET Technologies
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Pithos - Architecture and .NET Technologies

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Architecture and technologies used in the Windows client for Pithos, GRNET's cloud storage service

Architecture and technologies used in the Windows client for Pithos, GRNET's cloud storage service

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  • 1. Architecture and .NET TechnologiesPanagiotis KanavosPITHOS
  • 2.  Object storage similar to Amazon S3/Azure Blob storage A service of Synnefo Written in Python Clients for Web, Windows, iOS, Android, Linux
  • 3. Synnefo
  • 4. Client API REST API based on OpenStack Object Storage API Accounts, Containers without Folders GET for data, object info PUT, POST for uploads and data updates
  • 5. Structure
  • 6. API Extensions  Block Storage  Partial Upload/Download  Permissions, Versions  Metadata Queries  UUIDs for Object IDs  Object updates (copy, move)
  • 7. API Characteristics No folders! Placeholder directory object hold metadata Block updates ONLY Merkle hashing to detect modified blocks Hash using SHA256
  • 8. Merkle Hashing Top Hash Hash of #1- Hash of #2- 2 Hashes 3 Hashes Block #1 Block #2 Block #3 Block #4 Hash Hash Hash Hash
  • 9. Download ProcessGet Hashmap Calculate local Find different from server hashmap blocks Download Patch local file blocks with blocks
  • 10. Upload Process Server respondsCalculate local PUT to server with missing hashmap block hashes PUT missing Server responds blocks at Repeat from #2 201container level
  • 11. Pithos Client Multiple accounts per machine Synchronize local folder to Pithos account Detect local changes and upload Detect server changes and download Calculate Merkle Hash for each file
  • 12. Client Architecture UI Core Networking Storage WPF File Agent CloudFiles SQLite Poll Agent MVVM Network Agent SQL Server Caliburn HttpClient Compact Micro Status Agent
  • 13. Technologies .ΝΕΤ 4, due to Windows XP support req Visual Studio 2012 + Async Targeting Pack UI - Caliburn.Micro Concurrency - TPL, Parallel, Dataflow Network – HttpClient Hashing - OpenSSL – Faster than native provider for hashing Storage - NHibernate, SQLite/SQL Server Compact Logging - log4net
  • 14. The challenges Handle hundreds of file events Hashing of many large files Multiple slow connections to the server Unstable network Yet it shouldn’t hang Minimal UI with enough info for the user
  • 15. Event Handling Poll Agent Uploader/Downloader• Listen • Queue requests• Wait for Idle • Get Server • Process each file • Network ops for hashes files • Compare hashes • Identify changes File Agent Network Agent
  • 16. Events Handling(2) Use producer/consumer Store events in ConcurrentQueue Process ONLY after an idle timeout
  • 17. Merkle Hashing Why I hate Game of Thrones Asynchronous reading of blocks Block hashing in parallel Use OpenSSL to gain SSE2 etc Concurrency throttling Watch the memory consumption!
  • 18. Memory Leaks in a ManagedEnvironment!  4ΜΒ Blocks? Large Memory but …  Quickly reading 2GB in 64ΚΒ blocks?  Downloading 600ΜΒ in x KB blocks?  Huge number of small objects awaiting collection during CPU/IO intensive processing  Poor Garbage Collector can’t keep up!
  • 19. Hashing  100% CPU? Multicore is nice but …  Blocks the system when processing large files! Throttle parallel block hash ops Improvements:  Dynamically throttle «large» files  «Throttling» of File Read Ops
  • 20. Multiple slow network calls Every call a Task Concurrent REST calls per account and shared folder Task.WhenAll to process results at end of poll
  • 21. Unstable network Use System.Net.Http.HttpClient Store downloaded blocks in .pithos.cache folder Check and reuse orphans Asynchronous Retry of calls
  • 22. Resistance to crashes Use Transactional NTFS where available Thanks MS for killing it! Modify a copy File.Replace otherwise
  • 23. Should not hang Use independent agents Asynchronous operations wherever possible Use async/await for more readable code Must always .ConfigureAwait(false)! BE CAREFULL of async void
  • 24. Minimal UI Use WPF, MVVM Use Progress to update the UI  Part of .NET 4.5, backported to 4 The Icon is the Shell! Lack of good WPF Notification Icon Problematic Data Binding in menus
  • 25. SQLite or Compact CE?  Initially SQLite -> Staleness problems (DUH !)  Write Ahead logging, means you can see stale data  Switch to SQL Compact to allow concurrent updates (duh ?)  Really needed better caching?  Akavache?  A Document DB is better suited
  • 26. Next Steps File Manager UI General Cleanup (DUH!) Bring back Unit Tests (Duh ?) Mock Server  WebAPI? scriptcs? Yumm! Create a separate Pithos library Windows RT, Windows Phone clients  AFTER the cleanup
  • 27. Links for Pithos Pithos trial http://pithos.okeanos.io Synnefo Documentation http://www.synnefo.org/docs/synnefo/latest/ind ex.html Pithos API Documentation http://www.synnefo.org/docs/pithos/latest/index .html Pithos Windows Client https://code.grnet.gr/projects/pithos-ms-client
  • 28. Useful Links Parallel FX Team blog http://blogs.msdn.com/b/pfxteam Caliburn.Micro http://caliburnmicro.codeplex.com/ Ayende’s BufferPool http://ayende.com/blog/4827/answer- stopping-the-leaks
  • 29. Useful Books C# 5 in a Nutshell, O’Riley Parallel Programming with .NET, Microsoft• Pro Parallel Programming with C#, Wiley• Concurrent Programming on Windows, Pearson• The Art of Concurrency, O’Reilly