[#23695] docdb: Improve help strings for tablet replica limit flags.

Summary:
Adds additional detail to the main flag. Tweaks help strings for the other flags.
Jira: DB-12604

Test Plan: n/a

Reviewers: mlillibridge

Reviewed By: mlillibridge

Subscribers: slingam, asrivastava, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D37615

src/yb/common/tablet_limits.cc

@@ -18,12 +18,12 @@
 #include "yb/util/size_literals.h"
 
 DEFINE_RUNTIME_uint32(tablet_replicas_per_gib_limit, 1024 / 0.7,
-    "The maximum number of tablets the cluster can support per GiB of RAM reserved by TServers for "
-    "tablet overheads. 0 means no limit.");
+    "The maximum number of tablets the universe can support per GiB of RAM reserved by TServers "
+    "for tablet overheads. 0 means no limit.");
 TAG_FLAG(tablet_replicas_per_gib_limit, advanced);
 
 DEFINE_RUNTIME_uint32(tablet_replicas_per_core_limit, 0,
-    "The maximum number of tablets the cluster can support per vCPU being used by TServers. 0 "
+    "The maximum number of tablets the universe can support per vCPU being used by TServers. 0 "
     "means no limit.");
 TAG_FLAG(tablet_replicas_per_core_limit, advanced);
 

src/yb/master/tablet_creation_limits.cc

@@ -20,7 +20,10 @@
 #include "yb/util/atomic.h"
 
 DEFINE_RUNTIME_bool(enforce_tablet_replica_limits, false,
-                    "Whether to enforce the tablet replica limits.");
+    "When set, create table and split tablet operations will be blocked if they would cause the "
+    "total number of tablet replicas running in the universe to be too large. The limit for the "
+    "maximum number of tablet replicas the universe can support is set by the flags "
+    "tablet_replicas_per_gib_limit and tablet_replicas_per_core_limit.");
 TAG_FLAG(enforce_tablet_replica_limits, advanced);
 
 namespace yb::master {

src/yb/master/tablet_split_manager.cc

@@ -113,9 +113,9 @@ TAG_FLAG(pitr_split_disable_check_freq_ms, advanced);
 
 DEFINE_RUNTIME_bool(
     split_respects_tablet_replica_limits, false,
-    "Whether to check the cluster tablet replica limit before splitting a tablet. If true, the "
-    "system will no longer split tablets when the limit machinery determines the cluster cannot "
-    "support any more tablet replicas.");
+    "Whether to check the universe tablet replica limit before splitting a tablet. When this flag "
+    "and enforce_tablet_replica_limits are both true, the system will no longer split tablets when "
+    "the limit machinery determines the universe cannot support any more tablet replicas.");
 TAG_FLAG(split_respects_tablet_replica_limits, advanced);
 
 METRIC_DEFINE_gauge_uint64(server, automatic_split_manager_time,