# Second replica fails handshake (#HD5) **URL:** \ **Category:** Challenges\ **Tags:** challenge:redis\ **Created:** [January 15, 2025, 10:21pm UTC](https://forum.codecrafters.io/t/second-replica-fails-handshake-hd5/4216 "2025-01-15T22:21:14Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![hlud6646](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/hlud6646/32/1151_2.png) [@hlud6646](https://forum.codecrafters.io/u/hlud6646)\ **Post date:** [January 15, 2025, 10:21pm UTC](https://forum.codecrafters.io/t/second-replica-fails-handshake-hd5/4216/1 "2025-01-15T22:21:14Z")
I’m stuck on Stage #(#HD5 Multi Replica Command Propagation). ## Problem This post follows on from [https://forum.codecrafters.io/t/second-replica-fails-handshake-in-redis-challenge-hd5/3854](https://forum.codecrafters.io/t/second-replica-fails-handshake-in-redis-challenge-hd5/3854). The problem, as in that thread, is that I am able to spin up multiple replicas locally, with ```auto Terminal 1: ./your_program Terminal 2: ./your_program --port 1234 --replicaof "localhost 6379" Terminal 3: ./your_program --port 1235 --replicaof "localhsot 6379" ``` with successful handshakes and write requests to the master propagated to the slaves, but that the corresponding test stage fails. ## Attempted Fix In that post @andy1li suggested moving away from using `BufferedReader` and `readLine`. I have refactored the project, relying on the more primitive `InputStream.read()`. The original problem persists ## Logs From the master: ```auto Bound to port 6379. Waiting for connections. Accepted connection from Socket[addr=/127.0.0.1,port=54530,localport=6379] Received Ping [List()] Sending response to client at 54530. Received Replconf [List(listening-port, 1234)] Adding Socket[addr=/127.0.0.1,port=54530,localport=6379] to slaves. Sending response to client at 54530. Received Replconf [List(capa, psync2)] Sending response to client at 54530. Sending response to client at 54530. Sending RDB to slave: 54530 Accepted connection from Socket[addr=/127.0.0.1,port=50850,localport=6379] Received Ping [List()] Sending response to client at 50850. Received Replconf [List(listening-port, 1235)] Adding Socket[addr=/127.0.0.1,port=50850,localport=6379] to slaves. Sending response to client at 50850. Received Replconf [List(capa, psync2)] Sending response to client at 50850. Sending response to client at 50850. Sending RDB to slave: 50850 Accepted connection from Socket[addr=/127.0.0.1,port=33302,localport=6379] Received Set [List(asd, qwe)] Sending response to client at 33302. Propogating write request to 2 replicas. Propogating req to socket Socket[addr=/127.0.0.1,port=54530,localport=6379] Propogating req to socket Socket[addr=/127.0.0.1,port=50850,localport=6379] End of input stream. Closing socket. Accepted connection from Socket[addr=/127.0.0.1,port=43506,localport=6379] Received Set [List(foo, bar)] Sending response to client at 43506. Propogating write request to 2 replicas. Propogating req to socket Socket[addr=/127.0.0.1,port=54530,localport=6379] Propogating req to socket Socket[addr=/127.0.0.1,port=50850,localport=6379] End of input stream. Closing socket. ``` From the 1st slave: ```auto Bound to port 1234. [Handshake] Starting handshake. [Handshake] Opened socket Socket[addr=localhost/127.0.0.1,port=6379,localport=54530] [Handshake] Sending PING to 6379 [Handshake] Received PONG [Handshake] Sending first replconf to 6379 [Handshake] Received OK [Handshake] Sending second replconf to 6379 [Handshake] Received OK [Handshake] Sending psync to 6379 [Handshake] Receiving Database... [Handshake] Received 88 bytes of database. [Handshake] Handshake complete! Waiting for requests. Accepted connection from 6379 with acceptWriteRequests = true Received Set [List(asd, qwe)] Received Set [List(foo, bar)] ``` From the second slave: ```auto Bound to port 1235. [Handshake] Starting handshake. [Handshake] Opened socket Socket[addr=localhost/127.0.0.1,port=6379,localport=50850] [Handshake] Sending PING to 6379 [Handshake] Received PONG [Handshake] Sending first replconf to 6379 [Handshake] Received OK [Handshake] Sending second replconf to 6379 [Handshake] Received OK [Handshake] Sending psync to 6379 [Handshake] Receiving Database... [Handshake] Received 88 bytes of database. [Handshake] Handshake complete! Waiting for requests. Accepted connection from 6379 with acceptWriteRequests = true Received Set [List(asd, qwe)] Received Set [List(foo, bar)] ``` and finally the output of `codecrafters test`: ```auto ...(build steps)... [tester::#HD5] Running tests for Stage #HD5 (Replication - Multi Replica Command Propagation) [tester::#HD5] $ ./your_program.sh --port 6379 [your_program] Bound to port 6379. [your_program] Waiting for connections. [tester::#HD5] [handshake] Creating replica: 1 [tester::#HD5] [handshake] replica-1: $ redis-cli PING [tester::#HD5] [handshake] replica-1: Sent bytes: "*1\r\n$4\r\nPING\r\n" [your_program] Accepted connection from Socket[addr=/127.0.0.1,port=46370,localport=6379] [your_program] Accepted connection from Socket[addr=/127.0.0.1,port=46374,localport=6379] [your_program] Received Ping [List()] [your_program] Sending response to client at 46374. [tester::#HD5] [handshake] replica-1: Received bytes: "+PONG\r\n" [tester::#HD5] [handshake] replica-1: Received RESP simple string: "PONG" [tester::#HD5] [handshake] Received "PONG" [tester::#HD5] [handshake] replica-1: > REPLCONF listening-port 6380 [tester::#HD5] [handshake] replica-1: Sent bytes: "*3\r\n$8\r\nREPLCONF\r\n$14\r\nlistening-port\r\n$4\r\n6380\r\n" [your_program] Received Replconf [List(listening-port, 6380)] [your_program] Adding Socket[addr=/127.0.0.1,port=46374,localport=6379] to slaves. [your_program] Sending response to client at 46374. [tester::#HD5] [handshake] replica-1: Received bytes: "+OK\r\n" [tester::#HD5] [handshake] replica-1: Received RESP simple string: "OK" [tester::#HD5] [handshake] Received "OK" [tester::#HD5] [handshake] replica-1: > REPLCONF capa psync2 [tester::#HD5] [handshake] replica-1: Sent bytes: "*3\r\n$8\r\nREPLCONF\r\n$4\r\ncapa\r\n$6\r\npsync2\r\n" [your_program] Received Replconf [List(capa, psync2)] [tester::#HD5] [handshake] replica-1: Received bytes: "+OK\r\n" [tester::#HD5] [handshake] replica-1: Received RESP simple string: "OK" [your_program] Sending response to client at 46374. [tester::#HD5] [handshake] Received "OK" [tester::#HD5] [handshake] replica-1: > PSYNC ? -1 [tester::#HD5] [handshake] replica-1: Sent bytes: "*3\r\n$5\r\nPSYNC\r\n$1\r\n?\r\n$2\r\n-1\r\n" [your_program] Sending response to client at 46374. [your_program] Sending RDB to slave: 46374 [tester::#HD5] [handshake] replica-1: Received bytes: "+FULLRESYNC mgwcM0vHZba5zg7bDypkRWmIopxi4V5EBIJT8y75 0\r\n" [tester::#HD5] [handshake] replica-1: Received RESP simple string: "FULLRESYNC mgwcM0vHZba5zg7bDypkRWmIopxi4V5EBIJT8y75 0" [tester::#HD5] [handshake] Received "FULLRESYNC mgwcM0vHZba5zg7bDypkRWmIopxi4V5EBIJT8y75 0" [tester::#HD5] [handshake] Reading RDB file... [tester::#HD5] [handshake] replica-1: Received bytes: "$88\r\nREDIS0011\xfa\tredis-ver\x057.2.0\xfa\nredis-bits\xc0@\xfa\x05ctime\xc2m\b\xbce\xfa\bused-mem°\xc4\x10\x00\xfa\baof-base\xc0\x00\xff\xf0n;\xfe\xc0\xffZ\xa2" [tester::#HD5] [handshake] Received RDB file [tester::#HD5] Creating replica: 2 [tester::#HD5] [handshake] replica-2: $ redis-cli PING [tester::#HD5] [handshake] replica-2: Sent bytes: "*1\r\n$4\r\nPING\r\n" [tester::#HD5] Received: "" (no content received) [tester::#HD5] ^ error [tester::#HD5] Error: Expected start of a new RESP2 value (either +, -, :, $ or *) [tester::#HD5] Test failed [tester::#HD5] Terminating program [your_program] End of input stream. Closing socket. [your_program] Accepted connection from Socket[addr=/127.0.0.1,port=46382,localport=6379] [your_program] Received Ping [List()] [your_program] Sending response to client at 46382. [tester::#HD5] Program terminated successfully ``` Any help would be greatly appreciated! ---
**Author:** ![andy1li](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/andy1li/32/10_2.png) [@andy1li](https://forum.codecrafters.io/u/andy1li)\ **Post date:** [January 16, 2025, 4:09am UTC](https://forum.codecrafters.io/t/second-replica-fails-handshake-hd5/4216/2 "2025-01-16T04:09:34Z")
I’ll take a look shortly. ---
**Author:** ![andy1li](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/andy1li/32/10_2.png) [@andy1li](https://forum.codecrafters.io/u/andy1li)\ **Post date:** [January 16, 2025, 11:29am UTC](https://forum.codecrafters.io/t/second-replica-fails-handshake-hd5/4216/4 "2025-01-16T11:29:28Z")
Hi @hlud6646, I added some logs, and it seems that `Future` hangs when the second replica tries to send PING. ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/a/a4a8c2243b3c745679f50ad2f17d96d93a667592.png) `Future` only continues to execute after our tester tried to terminate your program: ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/4/4b571d927008149a17d574daa461f3c6a8534f8c.png) * * * However, the issue can be resolved by using `Thread` : ```auto val clientThread = new Thread(() => { handleClient(clientSocket, acceptWriteRequests = true) }) clientThread.start() ``` ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/2/26190daa8861912c555af45ef710002609333b54.png) * * * But why? It seems that the default size of the thread pool for `Future` is determined by the number of CPU cores: ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/d/dc56456486cb38ea1470e88f0e9b3c1a021d776a.png) However, the CPUs of our testers only have 2 cores, which makes them unable to handle a 3rd connection: ![image](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/2X/e/ed166edaf6982f4c1414a9016f10f72a64aa47a8.png) 1. ✅ Client 2. ✅ Replica 1 3. ❌ Replica 2 ---
**Author:** ![hlud6646](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/hlud6646/32/1151_2.png) [@hlud6646](https://forum.codecrafters.io/u/hlud6646)\ **Post date:** [January 16, 2025, 8:51pm UTC](https://forum.codecrafters.io/t/second-replica-fails-handshake-hd5/4216/6 "2025-01-16T20:51:43Z")
Fantastic. Thank you Andy for another instant reply! Serves me right for ignoring all the warnings about blindly importing the default execution context! ---
**Author:** ![hlud6646](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/hlud6646/32/1151_2.png) [@hlud6646](https://forum.codecrafters.io/u/hlud6646)\ **Post date:** [January 17, 2025, 4:04am UTC](https://forum.codecrafters.io/t/second-replica-fails-handshake-hd5/4216/7 "2025-01-17T04:04:31Z")
One other thing @andy1li How do you get that cool looking italic font for classes 😂 ---
**Author:** ![andy1li](https://yyz1.discourse-cdn.com/flex003/user_avatar/forum.codecrafters.io/andy1li/32/10_2.png) [@andy1li](https://forum.codecrafters.io/u/andy1li)\ **Post date:** [January 17, 2025, 11:55am UTC](https://forum.codecrafters.io/t/second-replica-fails-handshake-hd5/4216/8 "2025-01-17T11:55:46Z")
Oh, it’s part of the font I use. Here’re some fonts that support cursive italics: [https://www.reddit.com/r/ProgrammingFonts/comments/1foeqzt/cursive\_italic\_font/](https://www.reddit.com/r/ProgrammingFonts/comments/1foeqzt/cursive_italic_font/) ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex003/uploads/codecrafters/original/3X/7/0/700657133935c15703e22c7c8870394f6e6dc27d.svg) [@system](https://forum.codecrafters.io/u/system)\ **Post date:** [January 22, 2025, 11:56am UTC](https://forum.codecrafters.io/t/second-replica-fails-handshake-hd5/4216/9 "2025-01-22T11:56:25Z")
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