Add a caution about REALLOCATE DATABASES moving too much (#1762)

If there are lots of databases to move, an unbounded REALLOCATE can be
stressful for the cluster and the databases involved. With the newly
public limited reallocate procedures, they provide a gentler way to
achieve the balancing incrementally.

Author: nick-giles-neo

modules/ROOT/pages/clustering/databases.adoc

@@ -166,7 +166,8 @@ To rebalance all database allocations across the cluster, for example, because y
 [[reallocate-databases-procedure]]
 === Reallocate databases using a procedure
 
-You can use the procedure xref:reference/procedures.adoc#procedure_dbms_cluster_reallocateDatabase[`dbms.cluster.reallocateDatabase()`] to offload a specific database from all servers containing it onto new servers or xref:reference/procedures.adoc#procedure_dbms_cluster_reallocateNumberOfDatabases[dbms.cluster.reallocateNumberOfDatabases] to rebalance all database allocations across the cluster and relieve overloaded servers.
+You can use the procedure xref:reference/procedures.adoc#procedure_dbms_cluster_reallocateDatabase[`dbms.cluster.reallocateDatabase`] to rebalance a specific database across the cluster, or xref:reference/procedures.adoc#procedure_dbms_cluster_reallocateNumberOfDatabases[`dbms.cluster.reallocateNumberOfDatabases`] to rebalance a number of database allocations across the cluster and relieve overloaded servers.
+Note that if the cluster is already balanced, no reallocations will happen when running these procedures.
 These procedures do not require a server name and can be executed with or without a dry run.
 
 [NOTE]
@@ -202,6 +203,12 @@ neo4j@system> CALL dbms.cluster.reallocateNumberOfDatabases(3);
 You can use the Cypher command `REALLOCATE DATABASES` to rebalance all database allocations across the cluster and relieve overloaded servers.
 This command can also be used with `DRYRUN` to preview the new allocation of databases.
 
+[CAUTION]
+====
+`REALLOCATE DATABASES` on a large cluster with many databases has the potential to move a lot of allocations at once, which might stress the cluster.
+Consider starting with more limited reallocations, such as xref:reference/procedures.adoc#procedure_dbms_cluster_reallocateNumberOfDatabases[`dbms.cluster.reallocateNumberOfDatabases`] with a small number, and let the databases complete their reallocation before calling it again, until no more reallocations are necessary.
+====
+
 [NOTE]
 ====
 `DRYRUN` is available from Neo4j 5.2 and later.