Documentation and CHANGELOG.md entry for #2579. (#2618)

* Documentation and CHANGELOG.md entry for #2579.

Signed-off-by: Peter Štibraný <peter.stibrany@grafana.com>

* Document hidden option to configure caching bucket, to make it less hidden.

Signed-off-by: Peter Štibraný <peter.stibrany@grafana.com>

* Removed mention of caching_config.

Signed-off-by: Peter Štibraný <peter.stibrany@grafana.com>

* Added periods.

Signed-off-by: Peter Štibraný <peter.stibrany@grafana.com>

CHANGELOG.md

@@ -23,7 +23,8 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 - [#2502](https://github.com/thanos-io/thanos/pull/2502) Added `hints` field to `SeriesResponse`. Hints in an opaque data structure that can be used to carry additional information from the store and its content is implementation specific.
 - [#2521](https://github.com/thanos-io/thanos/pull/2521) Sidecar: add `thanos_sidecar_reloader_reloads_failed_total`, `thanos_sidecar_reloader_reloads_total`, `thanos_sidecar_reloader_watch_errors_total`, `thanos_sidecar_reloader_watch_events_total` and `thanos_sidecar_reloader_watches` metrics.
 - [#2412](https://github.com/thanos-io/thanos/pull/2412) ui: add React UI from Prometheus upstream. Currently only accessible from Query component as only `/graph` endpoint is migrated.
-- [#2532](https://github.com/thanos-io/thanos/pull/2532) Store: Added hidden option for experimental caching bucket, that can cache chunks into shared memcached. This can speed up querying and reduce number of requests to object storage.
+- [#2532](https://github.com/thanos-io/thanos/pull/2532) Store: Added hidden option `--store.caching-bucket.config=<yaml content>` (or `--store.caching-bucket.config-file=<file.yaml>`) for experimental caching bucket, that can cache chunks into shared memcached. This can speed up querying and reduce number of requests to object storage.
+- [#2579](https://github.com/thanos-io/thanos/pull/2579) Store: Experimental caching bucket can now cache metadata as well. Config has changed from #2532.
 
 ### Changed
 

docs/components/store.md

@@ -280,31 +280,45 @@ While the remaining settings are **optional**:
 
 ## Caching Bucket
 
-Thanos Store Gateway supports a "caching bucket" with chunks caching to speed up loading of chunks from TSDB blocks. Currently only memcached "backend" is supported:
+Thanos Store Gateway supports a "caching bucket" with chunks and metadata caching to speed up loading of chunks from TSDB blocks. To configure caching, one needs to use `--store.caching-bucket.config=<yaml content>` or `--store.caching-bucket.config-file=<file.yaml>`.
+
+Currently only memcached "backend" is supported:
 
 ```yaml
 backend: memcached
 backend_config:
   addresses:
     - localhost:11211
 
-caching_config:
-  chunk_subrange_size: 16000
-  max_chunks_get_range_requests: 3
-  chunk_object_size_ttl: 24h
-  chunk_subrange_ttl: 24h
+chunk_subrange_size: 16000
+max_chunks_get_range_requests: 3
+chunk_object_size_ttl: 24h
+chunk_subrange_ttl: 24h
+blocks_iter_ttl: 5m
+metafile_exists_ttl: 2h
+metafile_doesnt_exist_ttl: 15m
+metafile_content_ttl: 24h
+metafile_max_size: 1MiB
 ```
 
 `backend_config` field for memcached supports all the same configuration as memcached for [index cache](#memcached-index-cache).
 
-`caching_config` is a configuration for chunks cache and supports the following optional settings:
+Additional options to configure various aspects of chunks cache are available:
 
 - `chunk_subrange_size`: size of segment of chunks object that is stored to the cache. This is the smallest unit that chunks cache is working with.
 - `max_chunks_get_range_requests`: how many "get range" sub-requests may cache perform to fetch missing subranges.
 - `chunk_object_size_ttl`: how long to keep information about chunk file length in the cache.
 - `chunk_subrange_ttl`: how long to keep individual subranges in the cache.
 
-Note that chunks cache is an experimental feature, and these fields may be renamed or removed completely in the future.
+Following options are used for metadata caching (meta.json files, deletion mark files, iteration result):
+
+- `blocks_iter_ttl`: how long to cache result of iterating blocks.
+- `metafile_exists_ttl`: how long to cache information about whether meta.json or deletion mark file exists.
+- `metafile_doesnt_exist_ttl`: how long to cache information about whether meta.json or deletion mark file doesn't exist.
+- `metafile_content_ttl`: how long to cache content of meta.json and deletion mark files.
+- `metafile_max_size`: maximum size of cached meta.json and deletion mark file. Larger files are not cached.
+
+Note that chunks and metadata cache is an experimental feature, and these fields may be renamed or removed completely in the future.
 
 ## Index Header