How to Open a 50GB Log File — and Reopen It in 0.05 Seconds. A klogg Alternative, Benchmarked

If you searched for a klogg alternative , you probably already know klogg is good. It is fast, it is free, it is open source, and it runs on Windows, macOS and Linux. Most people who go looking for something else are not unhappy with klogg as a viewer. They are unhappy with one specific moment in their day: Opening the file again. You investigated a 48GB log yesterday. You closed it. This morning your colleague asks about a different error, and you have to wait through the whole index build a second time. On a USB HDD that is nine minutes of staring at a progress bar — and while it builds, klogg only shows you the beginning of the file. That is the problem this article is about. Below is a measured comparison on a real 47.73GB file, including the rows where klogg wins . The test File OpenStreetMap Japan japan-latest.osm — 47.73 GB, 892,239,125 lines Machine MacBook Air / Apple M4 (10 cores) / 32GB RAM Storage (measured with dd ) USB HDD 0.10 GB/s ／ USB SSD 0.41 GB/s ／ Internal SSD 3.29 GB/s Versions klogg 24.11.0 ／ UwView Pro Search hit counts were verified to match exactly across klogg, UwView Pro, and a direct search of the raw file — so we know both tools are answering the same question. The numbers klogg 24.11.0 UwView Pro Ratio First open HDD ~9 min ／ USB SSD ~110 s ／ Internal SSD ~15 s — every time HDD 10.6 min ／ USB SSD 138.5 s ／ Internal SSD 23.3 s — first time only klogg wins Reopening Same as the first open (re-indexes every time) 0.01–0.07 s ~1,250–50,000x Search, literal "Tokyo" ~585 s ／ 120–135 s ／ 15–20 s 74.8 s ／ 14.3 s ／ 5.1 s ~7.8x ／ ~9x ／ 3–4x Search, regex "Tok[yi]o" ≈ literal (I/O bound, pattern-independent) 29.8 s (USB SSD) ／ 11.0 s (Internal SSD) ~4.4x ／ ~1.5x Disk used to keep the file 48 GB (original required) 5.3 GB (original can be deleted) 1/9 Two things are worth saying plainly. klogg opens the file faster the first time. UwView Pro is slower on the first open because it is building a compressed cache while it reads. That is a real cost a