From tequilaron at gmail.com Mon Mar 4 21:57:26 2019 From: tequilaron at gmail.com (Ron Reynolds) Date: Mon, 4 Mar 2019 13:57:26 -0800 Subject: gc-log is within STW event? Message-ID: this blog https://engineering.linkedin.com/blog/2016/02/eliminating-large-jvm-gc-pauses-caused-by-background-io-traffic raises the question i my mind - why would logging to gc-log be done during a STW event at all? wouldn't it make sense to defer gc-logging to after the STW event? i suppose writing/flushing to gc-log would allow one to monitor GC progress DURING a STW event but is that worth the risk of being suspended during a STW by IO operations? sorry if this is the wrong channel to ask such questions. .....................ron. -------------- next part -------------- An HTML attachment was scrubbed... URL: From thomas.schatzl at oracle.com Thu Mar 14 09:47:18 2019 From: thomas.schatzl at oracle.com (Thomas Schatzl) Date: Thu, 14 Mar 2019 10:47:18 +0100 Subject: gc-log is within STW event? In-Reply-To: References: Message-ID: Hi Ron, On Mon, 2019-03-04 at 13:57 -0800, Ron Reynolds wrote: > this blog > https://engineering.linkedin.com/blog/2016/02/eliminating-large-jvm-gc-pauses-caused-by-background-io-traffic > raises the question i my mind - why would logging to gc-log be done > during a STW event at all? wouldn't it make sense to defer gc- > logging to after the STW event? i suppose writing/flushing to gc-log > would allow one to monitor GC progress DURING a STW event but is that > worth the risk of being suspended during a STW by IO operations? > sorry if this is the wrong channel to ask such questions. > .....................ron. > _______________________________________________ the GC log has traditionally been a tool for developer debugging, also ease of adding new events (i.e. a "printf" is easy to add) for the dev has been driving this. So can be quite important to not loose information. JFR has only been introduced much later for end-user use which implements the writing out in a separate thread as suggested as far as I know. So JFR events are not as detailed as the GC log at this time for most if not all collectors, but getting better with more recent releases. My personal opinion would be to add more JFR events instead of fixing the logging, but I think contributions in either direction are welcome. Thanks, Thomas