This removes Elasticsearch's filter cache and uses Lucene's instead. It has some
implications:
- custom cache keys (`_cache_key`) are unsupported
- decisions are made internally and can't be overridden by users ('_cache`)
- not only filters can be cached but also all queries that do not need scores
- parent/child queries can now be cached, however cached entries are only
valid for the current top-level reader so in practice it will likely only
be used on read-only indices
- the cache deduplicates filters, which plays nicer with large keys (eg. `terms`)
- better stats: we already had ram usage and evictions, but now also hit count,
miss count, lookup count, number of cached doc id sets and current number of
doc id sets in the cache
- dynamically changing the filter cache size is not supported anymore
Internally, an important change is that it removes the NoCacheFilter infrastructure
in favour of making Query.rewrite specializing the query for the current reader so
that it will only be cached on this reader (look for IndexCacheableQuery).
Note that consuming filters with the query API (createWeight/scorer) instead of
the filter API (getDocIdSet) is important for parent/child queries because
otherwise a QueryWrapperFilter(ParentQuery) would run the wrapped query per
segment while relations might be cross segments.
The `cluster.routing.allocation.balance.primary` setting has caused
a lot of confusion in the past while it has very little benefit form a
shard allocatioon point of view. Users tend to modify this value to
evently distribute primaries across the nodes which is dangerous since
a prmiary flag on it's own can trigger relocations. The primary flag for a shard
is should not have any impact on cluster performance unless the high level feature
suffereing from primary hotspots is buggy. Yet, this setting was intended to be a
tie-breaker which is not necessary anymore since the algorithm is deterministic.
This commit removes this setting entriely.
In some situations the shard balanceing weight delta becomes negative. Yet,
a negative delta is always treated as `well balanced` which is wrong. I wasn't
able to reproduce the issue in any way other than useing the real world data
from issue #9023. This commit adds a fix for absolute deltas as well as a base
test class that allows to build tests or simulations from the cat API output.
Closes#9023
`allocation.disable_new_allocation`, `allocation.disable_allocation`, `allocation.disable_replica_allocation`,
in favour for the enable allocation decider which has a single option `allocation.enable` wich can be set to the following values:
`none`, `new_primaries`, `primaries` and `all` (default).
Closes#4488
Robin Clarke
Simon Willnauer
Clinton Gormley
Adrien Grand
Lee Hinman
gseng
Michael McCandless
mahdeto
Nik Everett
bleskes
Luca Cavanna
Martijn van Groningen