Caleb Rackliffe maedhroz

CASSANDRA-15452 + CASSANDRA-20551: Read-Ahead Buffer for Compressed SSTable Scans

CASSANDRA-15452: Read-Ahead Buffer for Compressed SSTable Scans

1. Executive Summary

Introduces a thread-local read-ahead buffer for sequential scan workloads (compaction, range queries) over compressed SSTables. The existing path issued one channel.read() syscall per compressed chunk (~64 KiB); by pre-reading 256 KiB at a time and serving subsequent chunk reads from that in-process buffer, the patch cuts syscall count ~4× for sequential scans without touching the random-access path.

REPAIRED preview for fully-migrated tracked keyspaces — design summary

Goal and scope

Provide a REPAIRED preview that audits already-reconciled data across replicas for a tracked keyspace, validating that data backing reconciled offsets is byte-identical across replicas. Reject the operation if the keyspace isn't fully migrated to mutation tracking or if topology changes during any phase. ALL and UNREPAIRED previews on tracked keyspaces are a separate (simpler) design — out of scope here.

Operator-facing interface

Identical to classic REPAIRED preview:

	brew install hub

	...then in ~/.gitconfig...

	[alias]
	# public repo
	cpr = "!f() { curl https://github.com/cqlengine/cqlengine/pull/${1}.patch \| git apply -3 - ; }; f "

	# private repo
	spr = "!f() { hub apply -3 https://github.com/[your org]/[your project]/pull/${1} ; }; f "

	GOVERSION=$(brew list go \| head -n 1 \| cut -d '/' -f 6)
	export GOROOT=$(brew --prefix)/Cellar/go/$GOVERSION/libexec
	export GOPATH=/Users/[user]/go