So you are proposing writing two logs - one compressed and one uncompressed - to handle this. I am wondering what the break-even point of this would be. Many users use a size-base trigger instead so that a) the compression won't take long and b) manipulating a large file is not so much of a problem.
What has me wondering about the usefulness of this is that when the file gets so large that compression at rollover is a problem the file is probably too large to manipulate effectively in something like vi. Ralph Sent from my iPad > On May 28, 2014, at 10:27 AM, David Hoa <[email protected]> wrote: > > Yup, the tricky part would come on crash before close, interrupt, etc, > because I assume that that partially compressed file would be irrecoverable > (haven't verified this). Ideally, we'd be able to close it properly, but if > not, the log could, on startup, be recovered and compressed from the parallel > uncompressed log that was simultaneously being written by another/the same > appender. > > That would incur start up time to recover, which may be more acceptable in > the rare case of a crash. Else, if there's another compression technique that > leaves behind readable files even if not closed properly, that'd eliminate > the need for recovery. > > I'll open a jira ticket. Thanks for letting me share my thoughts on this. > > - David > > >> On Wed, May 28, 2014 at 9:39 AM, Matt Sicker <[email protected]> wrote: >> We can use GZIPOutputStream, DeflaterOutputStream, and ZipOutputStream all >> out of the box. >> >> What happens if you interrupt a stream in progress? No idea! But Gzip at >> least has CRC32 checksums on hand, so it can be detected if it's corrupted. >> We'll have to experiment a bit to see what really happens. I couldn't find >> anything in zlib.net's FAQ. >> >> >>> On 28 May 2014 08:56, Ralph Goers <[email protected]> wrote: >>> What would happen to the file if the system crashed before the file is >>> closed? Would the file be able to be decompressed or would it be corrupted? >>> >>> Sent from my iPad >>> >>>> On May 28, 2014, at 6:35 AM, Remko Popma <[email protected]> wrote: >>>> >>>> David, thank you for the clarification. I understand better what you are >>>> trying to achieve now. >>>> >>>> Interesting idea to have an appender that writes to a GZipOutputStream. >>>> Would you mind raising a Jira ticket for that feature request? >>>> >>>> I would certainly be interested in learning about efficient techniques for >>>> compressing very large files. Not sure if or how the dd/direct I/O >>>> mentioned in the blog you linked to could be leveraged from java. If you >>>> find a way that works well for log file rollover, and you're interested in >>>> sharing it, please let us know. >>>> >>>> >>>> >>>>> On Wed, May 28, 2014 at 3:42 PM, David Hoa <[email protected]> wrote: >>>>> Hi Remko, >>>>> >>>>> My point about gzip, which we've experienced, is that compressing very >>>>> large files (multi-GB) does have considerable impact on the system. The >>>>> dd/direct I/O workaround avoid putting that much log data into your >>>>> filesystem cache. For that problem, after I sent the email, I did look at >>>>> the log4j2 implementation, and saw that in >>>>> DefaultRolloverStrategy::rollover() it calls GZCompressionAction, so I >>>>> see how I can write my own strategy and Action to customize how gzip is >>>>> called. >>>>> >>>>> My second question was not about adding to existing gzip files; from what >>>>> I know that's not possible. But if the GZipOutputStream is kept open and >>>>> written to until closed by a rollover event, then the cost of gzipping is >>>>> amortized over time rather than incurred when the rollover event gets >>>>> triggered. The benefit is amortization of gzip so there's no resource >>>>> usage spike; downside would be writing both compressed and uncompressed >>>>> log files and maintaining rollover strategies for both of them. So a >>>>> built in appender that wrote directly to gz files would be useful for >>>>> this. >>>>> >>>>> Thanks, >>>>> David >>>>> >>>>> >>>>>> On Tue, May 27, 2014 at 4:52 PM, Remko Popma <[email protected]> >>>>>> wrote: >>>>>> Hi David, >>>>>> >>>>>> I read the blog post you linked to. It seems that the author was very, >>>>>> very upset that a utility called cp only uses a 512 byte buffer. He then >>>>>> goes on to praise gzip for having a 32KB buffer. >>>>>> So just based on your link, gzip is actually pretty good. >>>>>> >>>>>> That said, there are plans to improve the file rollover mechanism. These >>>>>> plans are currently spread out over a number of Jira tickets. One >>>>>> existing request is to delete archived log files that are older than >>>>>> some number of days. (https://issues.apache.org/jira/browse/LOG4J2-656, >>>>>> https://issues.apache.org/jira/browse/LOG4J2-524 ) >>>>>> This could be extended to cover your request to keep M compressed files. >>>>>> >>>>>> I'm not sure about appending to existing gzip files. Why is this >>>>>> desirable/What are you trying to accomplish with that? >>>>>> >>>>>> Sent from my iPhone >>>>>> >>>>>>> On 2014/05/28, at 3:22, David Hoa <[email protected]> wrote: >>>>>>> >>>>>>> hi Log4j Dev, >>>>>>> >>>>>>> I am interested in the log rollover and compression feature in log4j2. >>>>>>> I read the documentation online, and still have some questions. >>>>>>> >>>>>>> - gzipping large files has performance impact on latencies/cpu/file >>>>>>> cache, and there's a workaround for that using dd and direct i/o. Is it >>>>>>> possible to customize how log4j2 gzips files (or does log4j2 already do >>>>>>> this)? See this link for a description of the common problem. >>>>>>> http://kevinclosson.wordpress.com/2007/02/23/standard-file-utilities-with-direct-io/ >>>>>>> >>>>>>> - is it possible to use the existing appenders to output directly to >>>>>>> their final gzipped files, maintain M of those gzipped files, and >>>>>>> rollover/maintain N of the uncompressed logs? I suspect that the >>>>>>> complicated part would be in JVM crash recovery/ application restart. >>>>>>> Any suggestions on how best to add/extend/customize support for this? >>>>>>> >>>>>>> >>>>>>> Thanks, >>>>>>> David >> >> >> >> -- >> Matt Sicker <[email protected]> >
