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52 commits

Author SHA1 Message Date
Bjoern Rabenstein 6bc083f38b Major code cleanup in storage.
- Mostly docstring fixed/additions.
  (Please review these carefully, since most of them were missing, I
  had to guess them from an outsider's perspective. (Which on the
  other hand proves how desperately required many of these docstrings
  are.))

- Removed all uses of new(...) to meet our own style guide (draft).

- Fixed all other 'go vet' and 'golint' issues (except those that are
  not fixable (i.e. caused by bugs in or by design of 'go vet' and
  'golint')).

- Some trivial refactorings, like reorder functions, minor renames, ...

- Some slightly less trivial refactoring, mostly to reduce code
  duplication by embedding types instead of writing many explicit
  forwarders.

- Cleaned up the interface structure a bit. (Most significant probably
  the removal of the View-like methods from MetricPersistenc. Now they
  are only in View and not duplicated anymore.)

- Removed dead code. (Probably not all of it, but it's a first
  step...)

- Fixed a leftover in storage/metric/end_to_end_test.go (that made
  some parts of the code never execute (incidentally, those parts
  were broken (and I fixed them, too))).

Change-Id: Ibcac069940d118a88f783314f5b4595dce6641d5
2014-02-27 15:22:37 +01:00
Julius Volz 61d26e8445 Add optional sample replication to OpenTSDB.
Prometheus needs long-term storage. Since we don't have enough resources
to build our own timeseries storage from scratch ontop of Riak,
Cassandra or a similar distributed datastore at the moment, we're
planning on using OpenTSDB as long-term storage for Prometheus. It's
data model is roughly compatible with that of Prometheus, with some
caveats.

As a first step, this adds write-only replication from Prometheus to
OpenTSDB, with the following things worth noting:

1)
I tried to keep the integration lightweight, meaning that anything
related to OpenTSDB is isolated to its own package and only main knows
about it (essentially it tees all samples to both the existing storage
and TSDB). It's not touching the existing TieredStorage at all to avoid
more complexity in that area. This might change in the future,
especially if we decide to implement a read path for OpenTSDB through
Prometheus as well.

2)
Backpressure while sending to OpenTSDB is handled by simply dropping
samples on the floor when the in-memory queue of samples destined for
OpenTSDB runs full.  Prometheus also only attempts to send samples once,
rather than implementing a complex retry algorithm. Thus, replication to
OpenTSDB is best-effort for now.  If needed, this may be extended in the
future.

3)
Samples are sent in batches of limited size to OpenTSDB. The optimal
batch size, timeout parameters, etc. may need to be adjusted in the
future.

4)
OpenTSDB has different rules for legal characters in tag (label) values.
While Prometheus allows any characters in label values, OpenTSDB limits
them to a to z, A to Z, 0 to 9, -, _, . and /. Currently any illegal
characters in Prometheus label values are simply replaced by an
underscore. Especially when integrating OpenTSDB with the read path in
Prometheus, we'll need to reconsider this: either we'll need to
introduce the same limitations for Prometheus labels or escape/encode
illegal characters in OpenTSDB in such a way that they are fully
decodable again when reading through Prometheus, so that corresponding
timeseries in both systems match in their labelsets.

Change-Id: I8394c9c55dbac3946a0fa497f566d5e6e2d600b5
2014-01-02 18:21:38 +01:00