Yeah, with few more (and hopefuly last) things to add: Not flushing after every line doesn't seem to make a difference for FileOutputStream in isolated tests (I was getting identical times as with flushing) - unless buffering of course - but it does make difference with logback which uses this FileOutputStream. However logback wraps OutputStreamWriter around it and then it really makes that difference - and also results become very close (almost identical) to FileWriter then. Java 1.5 only: OutputStreamWriter/FileOutputStream immediateFlush: 8435 OutputStreamWriter/FileOutputStream no-flush: 1160 BufferedWriter/OutputStreamWriter/FileOutputStream no-flush: 922 FileWriter immediateFlush: 8271 FileWriter no-flush: 1150 BufferedWriter/FileWriter no-flush: 918 In real logging scenarios it looks to me that immediateFlush=false decreases times to 1/2-1/3 and buffering can give further 10-15% improvement with properly sized buffer. So I definitely vote for bringing at least the immediateFlush=false option back. Bringing back buffering would also be great as one can get a bit more performance out of it - and every little bit does matter for us here. :)