compactor, store-gateway: always upload sparse headers (#13089)

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#### What this PR does

follow-up of #10684. We've been running this at GL for some time without
problems. This is the next step towards removing the flag.

#### Which issue(s) this PR fixes or relates to

Fixes #<issue number>

#### Checklist

- [ ] Tests updated.
- [ ] Documentation added.
- [x] `CHANGELOG.md` updated - the order of entries should be
`[CHANGE]`, `[FEATURE]`, `[ENHANCEMENT]`, `[BUGFIX]`. If changelog entry
is not needed, please add the `changelog-not-needed` label to the PR.
- [ ]
[`about-versioning.md`](https://github.com/grafana/mimir/blob/main/docs/sources/mimir/configure/about-versioning.md)
updated with experimental features.

---------

Signed-off-by: Dimitar Dimitrov <dimitar.dimitrov@grafana.com>

Author: dimitarvdimitrov

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Grafana Mimir
 
 * [BUGFIX] Compactor: Fix potential concurrent map writes. #13053
+* [ENHANCEMENT] Compactor, Store-gateway: Change default value of `-compactor.upload-sparse-index-headers` to `true`. This improves lazy loading performance in the store-gateway. #13089
 
 ### Mixin
 

cmd/mimir/config-descriptor.json

@@ -11630,7 +11630,7 @@
           "required": false,
           "desc": "If enabled, the compactor constructs and uploads sparse index headers to object storage during each compaction cycle. This allows store-gateway instances to use the sparse headers from object storage instead of recreating them locally.",
           "fieldValue": null,
-          "fieldDefaultValue": false,
+          "fieldDefaultValue": true,
           "fieldFlag": "compactor.upload-sparse-index-headers",
           "fieldType": "boolean",
           "fieldCategory": "experimental"

cmd/mimir/help-all.txt.tmpl

@@ -1166,7 +1166,7 @@ Usage of ./cmd/mimir/mimir:
   -compactor.update-blocks-concurrency int
     	Number of goroutines to use when updating blocks metadata during bucket index updates. (default 1)
   -compactor.upload-sparse-index-headers
-    	[experimental] If enabled, the compactor constructs and uploads sparse index headers to object storage during each compaction cycle. This allows store-gateway instances to use the sparse headers from object storage instead of recreating them locally.
+    	[experimental] If enabled, the compactor constructs and uploads sparse index headers to object storage during each compaction cycle. This allows store-gateway instances to use the sparse headers from object storage instead of recreating them locally. (default true)
   -config.expand-env
     	Expands ${var} or $var in config according to the values of the environment variables.
   -config.file value

docs/sources/mimir/configure/configuration-parameters/index.md

@@ -5379,7 +5379,7 @@ sharding_ring:
 # store-gateway instances to use the sparse headers from object storage instead
 # of recreating them locally.
 # CLI flag: -compactor.upload-sparse-index-headers
-[upload_sparse_index_headers: <boolean> | default = false]
+[upload_sparse_index_headers: <boolean> | default = true]
 ```
 
 ### store_gateway

operations/mimir/mimir-flags-defaults.json

@@ -821,6 +821,7 @@
   "compactor.ring.wait-active-instance-timeout": 600000000000,
   "compactor.ring.auto-forget-unhealthy-periods": 10,
   "compactor.compaction-jobs-order": "smallest-range-oldest-blocks-first",
+  "compactor.upload-sparse-index-headers": true,
   "store-gateway.sharding-ring.store": "memberlist",
   "store-gateway.sharding-ring.prefix": "collectors/",
   "store-gateway.sharding-ring.consul.hostname": "localhost:8500",

pkg/compactor/compactor.go

@@ -161,7 +161,7 @@ func (cfg *Config) RegisterFlags(f *flag.FlagSet, logger log.Logger) {
 		"If 0, blocks will be deleted straight away. Note that deleting blocks immediately can cause query failures.")
 	f.DurationVar(&cfg.TenantCleanupDelay, "compactor.tenant-cleanup-delay", 6*time.Hour, "For tenants marked for deletion, this is the time between deletion of the last block, and doing final cleanup (marker files, debug files) of the tenant.")
 	f.BoolVar(&cfg.NoBlocksFileCleanupEnabled, "compactor.no-blocks-file-cleanup-enabled", false, "If enabled, will delete the bucket-index, markers and debug files in the tenant bucket when there are no blocks left in the index.")
-	f.BoolVar(&cfg.UploadSparseIndexHeaders, "compactor.upload-sparse-index-headers", false, "If enabled, the compactor constructs and uploads sparse index headers to object storage during each compaction cycle. This allows store-gateway instances to use the sparse headers from object storage instead of recreating them locally.")
+	f.BoolVar(&cfg.UploadSparseIndexHeaders, "compactor.upload-sparse-index-headers", true, "If enabled, the compactor constructs and uploads sparse index headers to object storage during each compaction cycle. This allows store-gateway instances to use the sparse headers from object storage instead of recreating them locally.")
 
 	// compactor concurrency options
 	f.IntVar(&cfg.MaxOpeningBlocksConcurrency, "compactor.max-opening-blocks-concurrency", 1, "Number of goroutines opening blocks before compaction.")

pkg/compactor/compactor_test.go

@@ -1769,6 +1769,8 @@ func prepareConfig(t *testing.T) Config {
 	// The new default is 25m, but tests rely on the previous value of 0s
 	compactorCfg.CompactionWaitPeriod = 0
 
+	compactorCfg.SparseIndexHeadersSamplingRate = 32
+
 	return compactorCfg
 }