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Author	SHA1	Message	Date
Julius Volz	740d448983	Use custom timestamp type for sample timestamps and related code. So far we've been using Go's native time.Time for anything related to sample timestamps. Since the range of time.Time is much bigger than what we need, this has created two problems: - there could be time.Time values which were out of the range/precision of the time type that we persist to disk, therefore causing incorrectly ordered keys. One bug caused by this was: https://github.com/prometheus/prometheus/issues/367 It would be good to use a timestamp type that's more closely aligned with what the underlying storage supports. - sizeof(time.Time) is 192, while Prometheus should be ok with a single 64-bit Unix timestamp (possibly even a 32-bit one). Since we store samples in large numbers, this seriously affects memory usage. Furthermore, copying/working with the data will be faster if it's smaller. MEMORY USAGE RESULTS Initial memory usage comparisons for a running Prometheus with 1 timeseries and 100,000 samples show roughly a 13% decrease in total (VIRT) memory usage. In my tests, this advantage for some reason decreased a bit the more samples the timeseries had (to 5-7% for millions of samples). This I can't fully explain, but perhaps garbage collection issues were involved. WHEN TO USE THE NEW TIMESTAMP TYPE The new clientmodel.Timestamp type should be used whenever time calculations are either directly or indirectly related to sample timestamps. For example: - the timestamp of a sample itself - all kinds of watermarks - anything that may become or is compared to a sample timestamp (like the timestamp passed into Target.Scrape()). When to still use time.Time: - for measuring durations/times not related to sample timestamps, like duration telemetry exporting, timers that indicate how frequently to execute some action, etc. NOTE ON OPERATOR OPTIMIZATION TESTS We don't use operator optimization code anymore, but it still lives in the code as dead code. It still has tests, but I couldn't get all of them to pass with the new timestamp format. I commented out the failing cases for now, but we should probably remove the dead code soon. I just didn't want to do that in the same change as this. Change-Id: I821787414b0debe85c9fffaeb57abd453727af0f	11 years ago
Matt T. Proud	e86f4d9dfd	Convert time readers to represent time in UTC. Go's time.Time represents time as UTC in its fundamental data type. That said, when using ``time.Unix(...)``, it sets the zone for the time representation to the local. Unfortunately with diagnosis and our tests, it is a PITA to jump between various zones, even though the serialized version remains the same. To keep things easy, all places where times are generated or read are converted into UTC. These conversions are cheap, for ``Time.In`` merely changes a pointer reference in the struct, nothing more. This enables me to diagnose test failures with fixture data very easily.	12 years ago
Matt T. Proud	13ae29b304	Initial in-memory arena implementation. It is unbounded, and nothing uses it except for a gating flag in main.	12 years ago
Julius Volz	d67e4b9131	Address outstanding comments from PR/47 and other cleanups.	12 years ago
Matt T. Proud	44f8802ae7	Add Apache License 2.0 boilerplate.	12 years ago
Matt T. Proud	6072143505	Initial commit of external resources.	12 years ago