Wow. I didn’t expect them to be that much faster. That makes me very reluctant to be ok with switching.
Ralph > On Oct 14, 2024, at 1:51 PM, Volkan Yazıcı <vol...@yazi.ci.INVALID> wrote: > > Some results using Java 17: > > > *yyyy-MM-dd'T'HH:mm:ss.SSS*DateTimeFormatter 2.844 ± 0.310 ops/ms > FastDateFormat 6.847 ± 1.302 ops/ms > FixedDateFormat 39.497 ± 6.423 ops/ms > > *HH:mm:ss.SSS* > DateTimeFormatter 3.881 ± 0.447 ops/ms > FastDateFormat 10.862 ± 1.915 ops/ms > FixedDateFormat 39.618 ± 9.318 ops/ms > > > I used distinct instants within the same day to avoid cache misses in > `FixedDateFormat`'s cache on the `yyyy-MM-dd` part, which is updated daily > at midnight. That is why `FixedDF` figures are more or less the same for > both patterns. > > On Mon, Oct 14, 2024 at 9:48 PM Ralph Goers <ralph.go...@dslextreme.com> > wrote: > >> Before I can weigh in one way or another I would need to know what the >> performance difference is between DateTimeFormatter and the Fixed and Fast >> classes, at least where they are working properly. Any such test should >> include the caching otherwise you would be comparing worst case performance. >> >> Ralph >> >>> On Oct 14, 2024, at 12:30 PM, Volkan Yazıcı <vol...@yazi.ci.INVALID> >> wrote: >>> >>> *Abstract:* Log4j contains two custom date & time formatting classes. All >>> our competitors (Logback >>> < >> https://github.com/qos-ch/logback/blob/master/logback-core/src/main/java/ch/qos/logback/core/util/CachingDateFormatter.java >>> , >>> Tinylog >>> < >> https://github.com/tinylog-org/tinylog/blob/7590ad150b1523691ae6f26ae24a291b81d804c9/tinylog-api/src/main/java/org/tinylog/runtime/PreciseTimestampFormatter.java >>> , >>> etc.) use Java's `DateTimeFormatter` and I know of no user complaints >> about >>> their performance issues. Shall we switch to `DateTimeFormatter` as the >>> default in the next minor release and make the custom implementations >>> opt-in? >>> >>> Log4j ships two custom date & time formatting classes: >>> >>> - `FixedDateFormat` >>> - Supports a hardcoded list of formats >>> - Bug: Conflates `n` directive with `S` >>> - Bug: It cannot calculate DST correctly for all time zones >>> <https://github.com/apache/logging-log4j2/issues/2943> >>> - `FastDateFormat` >>> - Copied from Commons Lang in 2015 >>> >>> I recently ran a test comparing the output of these with >>> `DateTimeFormatter` – the difference is *big*! I can spend months fixing >>> these issues, but... Do we really need them? >>> >>> 1. No other competitors have such an optimization (both Logback >>> < >> https://github.com/qos-ch/logback/blob/master/logback-core/src/main/java/ch/qos/logback/core/util/CachingDateFormatter.java >>> >>> and Tinylog >>> < >> https://github.com/tinylog-org/tinylog/blob/7590ad150b1523691ae6f26ae24a291b81d804c9/tinylog-api/src/main/java/org/tinylog/runtime/PreciseTimestampFormatter.java >>> >>> use >>> `DateTimeFormatter`) >>> 2. Date & time formatting is very fragile (DST is more voodoo than >>> science) >>> 3. If date & time formatting during logging is found to be the >>> bottleneck of an application, shouldn't they instead encode it >> differently, >>> e.g., encoding epoch numbers? >>> 4. `DateTimeFormatter` performance will only get better over time >>> >>> Hence, I propose switching all layouts to use `DateTimeFormatter`, unless >>> the `log4j.time.legacyFormatterEnabled` property is provided. Objections? >>> >>> Note that the caching optimization we have for the last formatted >> timestamp >>> will stay untouched. >> >>
