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 > <https://issues.apache.org/jira/browse/LOG4J2>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]>
