app/{vmstorage,vmselect}: disable vmstorage->vmselect RPC compression by default in order to improve query performance

docs/CHANGELOG.md

@@ -60,6 +60,7 @@ The sandbox cluster installation is running under the constant load generated by
 * FEATURE: [vmui](https://docs.victoriametrics.com/#vmui): add `-vmui.defaultTimezone` flag to set a default timezone. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5375) and [these docs](https://github.com/VictoriaMetrics/VictoriaMetrics/tree/master/app/vmui#timezone-configuration).
 * FEATURE: [vmui](https://docs.victoriametrics.com/#vmui): include UTC in the timezone selection dropdown for standardized time referencing. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5375).
 * FEATURE: add [VictoriaMetrics datasource](https://github.com/VictoriaMetrics/grafana-datasource) to docker compose environment. See [this pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/5363).
+* FEATURE: [VictoriaMetrics cluster](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html): disable compression for RPC responses sent from `vmstorage` to `vmselect`. This improves query performance at the cost of increased network bandwidth usage. The compression can be enabled back by passing `-rpc.disableCompression=false` command-line flag to `vmstorage`. The compression can be enabled back in [multi-level cluster setup](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#multi-level-cluster-setup) by passing `-clusternative.disableCompression=false` command-line flag to lower-level `vmselect` nodes.
 
 * BUGFIX: properly return errors from [export APIs](https://docs.victoriametrics.com/#how-to-export-time-series). Previously these errors were silently suppressed. See [this pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/5649).
 * BUGFIX: [VictoriaMetrics cluster](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html): properly return full results when `-search.skipSlowReplicas` command-line flag is passed to `vmselect` and when [vmstorage groups](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#vmstorage-groups-at-vmselect) are in use. Previously partial results could be returned in this case.

docs/Cluster-VictoriaMetrics.md

@@ -596,7 +596,6 @@ Some capacity planning tips for VictoriaMetrics cluster:
 - Query latency can be reduced by increasing CPU resources per each `vmselect` node, since each incoming query is processed by a single `vmselect` node. Performance for heavy queries scales with the number of available CPU cores at `vmselect` node, since `vmselect` processes time series referred by the query on all the available CPU cores.
 - If the cluster needs to process incoming queries at a high rate, then its capacity can be increased by adding more `vmselect` nodes, so incoming queries could be spread among bigger number of `vmselect` nodes.
 - By default `vminsert` compresses the data it sends to `vmstorage` in order to reduce network bandwidth usage. The compression takes additional CPU resources at `vminsert`. If `vminsert` nodes have limited CPU, then the compression can be disabled by passing `-rpc.disableCompression` command-line flag at `vminsert` nodes.
-- By default `vmstorage` compresses the data it sends to `vmselect` during queries in order to reduce network bandwidth usage. The compression takes additional CPU resources at `vmstorage`. If `vmstorage` nodes have limited CPU, then the compression can be disabled by passing `-rpc.disableCompression` command-line flag at `vmstorage` nodes.
 
 See also [resource usage limits docs](#resource-usage-limits).
 
@@ -1187,7 +1186,7 @@ Below is the output for `/path/to/vmselect -help`:
   -cluster.tlsKeyFile string
      Path to client-side TLS key file to use when connecting to -storageNode if -cluster.tls flag is set. See https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#mtls-protection . This flag is available only in VictoriaMetrics enterprise. See https://docs.victoriametrics.com/enterprise.html
   -clusternative.disableCompression
-     Whether to disable compression of the data sent to vmselect via -clusternativeListenAddr. This reduces CPU usage at the cost of higher network bandwidth usage
+     Whether to disable compression of the data sent to vmselect via -clusternativeListenAddr. This reduces CPU usage at the cost of higher network bandwidth usage (default true)
   -clusternative.maxConcurrentRequests int
      The maximum number of concurrent vmselect requests the server can process at -clusternativeListenAddr. It shouldn't be high, since a single request usually saturates a CPU core at the underlying vmstorage nodes, and many concurrently executed requests may require high amounts of memory. See also -clusternative.maxQueueDuration (default 32)
   -clusternative.maxQueueDuration duration
@@ -1608,7 +1607,7 @@ Below is the output for `/path/to/vmstorage -help`:
   -retentionTimezoneOffset duration
      The offset for performing indexdb rotation. If set to 0, then the indexdb rotation is performed at 4am UTC time per each -retentionPeriod. If set to 2h, then the indexdb rotation is performed at 4am EET time (the timezone with +2h offset)
   -rpc.disableCompression
-     Whether to disable compression of the data sent from vmstorage to vmselect. This reduces CPU usage at the cost of higher network bandwidth usage
+     Whether to disable compression of the data sent from vmstorage to vmselect. This reduces CPU usage at the cost of higher network bandwidth usage (default true)
   -search.maxConcurrentRequests int
      The maximum number of concurrent vmselect requests the vmstorage can process at -vmselectAddr. It shouldn't be high, since a single request usually saturates a CPU core, and many concurrently executed requests may require high amounts of memory. See also -search.maxQueueDuration (default 32)
   -search.maxQueueDuration duration