This isn't going to noticeably improve performance, but enables future
optimisations, e.g. more compact representations of LatestMaps where
many/all entries share the same timestamp.
We want the middle ground between a small compression size, a fast
compression time and a fast decompression time.
Tests suggest that the default compression level is better than the
maximum compression level: although the reports are 4% bigger and
decompress slower, they compress 33% faster.
See discussion on https://github.com/weaveworks/scope/issues/1457#issuecomment-293288682
By reducing the number of times we refer to every topology by name line by line,
we make it easier to add new topologies, reduce the risk of bugs where a topology is not listed,
and reduce the risk of the repeated lines getting out of sync with each other.
We introduce two new methods to assist this:
WalkPairedTopologies, a modified WalkTopologies that gives the called function
the same topology from two reports. This is used, for example, to implement Copy and Merge.
TopologyMap, which returns a map of all topologies by name. This is then used to implement all other methods.
This leaves only 4 instances of listing topologies:
In the consts at the top of the file, to give it a name
In the struct itself
In the constructor, where we need to set per-topology settings
In TopologyMap
Structs like StringLatestMap now use ps.Map directly, which saves
a memory allocation for LatestEntry.Value to point to.
The values in the ps.Map are now pointers, which saves a memory
allocation indirecting a value type to an interface{}
This is important for two reasons:
* It prevents nasty false-equality bugs when two different services from different ECS clusters
are present in the same report
* It allows us to retrieve the cluster and service name - all the info we need to look up the service -
using only the node ID. This matters, for example, when trying to handle a control request.
The new probe will convert all node's LatestControls to Controls, so
the old app can consume them. Also, the new app will convert all
node's Controls to LatestControl, so it can consume the reports from
old probes.
This allows plugins to add controls to nodes that already have some
controls set by other plugin. Previously only the last plugin that
sets the controls in the node would have its controls visible. That
was because of NodeControls' Merge function that actually weren't
merging data from two inputs, but rather returning data that was newer
and discarding the older one.
This commit makes the LatestMap type a sort of a base class, that
should not be used directly. This also adds a generator for LatestMap
"concrete" types with a specific data type in the LatestEntry.
