The Backend Engineering Show with Hussein Nasser Hussein Nasser

In this episode of the backend engineering show I discuss consistent hashing a very important algorithm in distributed computing specially in database systems such as Apache Cassandra and DynamoDB.

0:00 Intro

2:00 Problem of Distributed Systems

5:00 When to Distribute

7:00 Simple Hashing

9:30 Where Simple Hashing Breaks

11:40 Consistent Hashing

18:00 Adding a Server

21:15 Removing a Server

22:30 Limitations


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In this episode of the backend engineering show I go through and discuss the Homa Protocol paper which attempts to replace TCP as a protocol in the data centers. I learned a lot from this paper, I have my criticisms of certain aspects, timestamps for topics discussed below.

It appears there is a path to replace TCP in the datacenter and professor John tries to explain this path.



Referenced materials mentioned in the episode

Overview paper

https://web.stanford.edu/~ouster/cgi-bin/papers/replaceTcp.pdf

Homa 2018 paper (Details)

https://people.csail.mit.edu/alizadeh/papers/homa-sigcomm18.pdf

NIC Offloading in Linux

https://en.wikipedia.org/wiki/TCP_offload_engine#Support_in_Linux

Curl disabling Nigel Algo

https://github.com/curl/curl/commit/4732ca5724072f132876f520c8f02c7c5b654d9

0:00 Intro

3:00 The nature of networking data center

5:30 TCP Segments

7:30 There is no “Request” in TCP

12:00 What so unique about Data centers?

14:00 Message Throughput vs Data throughput

18:25 Congestion Control

22:38 Homa’s Congestion Control

25:00 Server Core Load Balancing

28:30 NIC offloading

30:00 Everything Wrong about TCP

37:00 Why not QUIC?

40:00 Limitation of Streaming

44:10 Load Balancing Stream Reading

47:15 Can we treat Segments as Messages?

51:00 Dispatching Messages is Easier

53:00 Connection Orientation

1:00:00 Sender Driven Congestion Control

1:03:00 In Order Packet Delivery

1:07:00 DCTCP

1:08:30 Homa is Message Based

1:11:00 Home is Connection Less

1:12:00 Receiver Driven Congestion Control

1:15:19 Out of Order Packets

1:16:20 Homa API is not Compatible with TCP

1:17:40 Will Homa come to HTTP?

1:18:45 Conclusion


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ByteDance, the company behind TikTok is proposing few patches to the linux kernel to make kernel reboots via kexec go from 500ms down to 15 ms saving huge time in updating kernel on thousands of machines. Let us discuss this

0:00 Intro

1:30 Linux Kernel Reboot Options

2:30 how kexec works

4:00 The optimization

5:00 Going through the patch

6:00 Updating Servers at TikTok scale

9:00 Summary

https://www.phoronix.com/news/Bytedance-Faster-Kexec-Reboot

https://lore.kernel.org/lkml/20220725083904.56552-1-huangjie.albert@bytedance.com/


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We discuss the CVE-2022-2274 OpenSSL Vulnerability.

The OpenSSL 3.0.4 release introduced a serious bug in the RSA

implementation for X86_64 CPUs supporting the AVX512IFMA instructions.

This issue makes the RSA implementation with 2048 bit private keys

incorrect on such machines and memory corruption will happen during

the computation. As a consequence of the memory corruption an attacker

may be able to trigger a remote code execution on the machine performing

the computation.

0:00 Intro

1:00 CVE-2022-2274

3:00 AVX512IFMA CISC

5:00 How the bug works

7:10 How can it be triggered

Resources

https://www.openssl.org/news/secadv/20220705.txt

https://github.com/openssl/openssl/issues/18625

https://guidovranken.com/2022/06/27/notes-on-openssl-remote-memory-corruption/

https://eprint.iacr.org/2018/335

https://github.com/openssl/openssl/commit/4d8a88c134df634ba610ff8db1eb8478ac5fd345

https://linux.die.net/man/3/bn_internal

https://www.microfocus.com/documentation/enterprise-developer/ed60/ES-WIN/GUID-E3960B1E-C42E-4748-A5EB-6E12507C9CD7.html

https://www.microcontrollertips.com/risc-vs-cisc-architectures-one-better/

Fundamentals of Networking for Effective Backends udemy course (link redirects to udemy with coupon)

https://network.husseinnasser.com


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Postgres 15 introduces a new syntax to treat nulls as not distinct. This will allow developers to create a unique constraint on nullable fields and have inserts with nulls fail instead of having it allowed based on today's standard.

Fundamentals of Networking for Effective Backends udemy course (link redirects to udemy with coupon)

https://network.husseinnasser.com

Fundamentals of Database Engineering udemy course (link redirects to udemy with coupon)

https://database.husseinnasser.com



https://blog.rustprooflabs.com/2022/07/postgres-15-unique-improvement-with-null

https://www.postgresql.org/message-id/flat/84e5ee1b-387e-9a54-c326-9082674bde78%40enterprisedb.com




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memchr() is a function that searches in a memory block for a character, this has been recently improved in the latest linux patch and we can learn something from this improvement I think, lets discuss.

https://www.phoronix.com/scan.php?page=news_item&px=Linux-Kernel-Faster-memchr

Fundamentals of Networking for Effective Backends udemy course (link redirects to udemy with coupon)

https://network.husseinnasser.com


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