### 23.7.1 NDB Cluster Replication: Abbreviations and Symbols

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 Throughout this section, we use the following abbreviations or symbols for referring to the source and replica clusters, and to processes and commands run on the clusters or cluster nodes:

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**Table 23.68 Abbreviations used throughout this section referring to source and replica clusters, and to processes and
commands run on cluster nodes**

|Symbol or Abbreviation|                                    Description (Refers to...)                                    |
|----------------------|--------------------------------------------------------------------------------------------------|
|        *`S`*         |                     The cluster serving as the (primary) replication source                      |
|        *`R`*         |                           The cluster acting as the (primary) replica                            |
|    `shell*`S`*>`     |                         Shell command to be issued on the source cluster                         |
|    `mysql*`S`*>`     |MySQL client command issued on a single MySQL server running as an SQL node on the source cluster |
|    `mysql*`S*`*>`    |MySQL client command to be issued on all SQL nodes participating in the replication source cluster|
|    `shell*`R`*>`     |                        Shell command to be issued on the replica cluster                         |
|    `mysql*`R`*>`     |MySQL client command issued on a single MySQL server running as an SQL node on the replica cluster|
|    `mysql*`R*`*>`    |     MySQL client command to be issued on all SQL nodes participating in the replica cluster      |
|        *`C`*         |                                   Primary replication channel                                    |
|        *`C'`*        |                                  Secondary replication channel                                   |
|        *`S'`*        |                                   Secondary replication source                                   |
|        *`R'`*        |                                        Secondary replica                                         |

