[THRIFT-5231] Improve Haskell parsing performance

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 0.13.0
• Component/s: Haskell - Library
• Assignee: Unassigned
• Reporter: Philipp Hausmann
• Created: 08/Jun/20 08:47
• Updated: 22/Mar/21 08:47
• Resolved: 22/Mar/21 08:47

Description

We are using Thrift for (de-)serializing some Kafka messages and noticed that already at low throughput (1000 messages / second) a lot of CPU is used.

 

I did a small benchmark just parsing a single T_BINARY value and if I use `readVal` for that it takes ~3ms per iteration. If instead I directly run the attoparsec parser, it only takes ~ 300ns. This is a difference by 4 orders of magnitude! Some difference is reasonable as when using `readVal` some IO and shuffling around bytestrings is involved, but the difference looks huge.

 

I strongly suspect the implementation of `runParser` is not optimal. Basically it runs the parser with 1 Byte, and until it succeeds it appends 1 byte and retries. This means that for a value of size 1024 bytes, we e.g. try to parse it 1023 times. This seems rather inefficient.

 

I am not really sure how to best fix this. In principle, it makes sense to feed bigger chunks to attoparsec and store the left-overs somewhere for the next parse. However, if we store it in the transport or protocol we have to implement it for each transport/protocol. Maybe an API change is necessary?