# Quorum-based Synchronous Replication

> Source chapter 3.7 for PostgreSQL 10.

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LLMS index: [llms.txt](/en/llms.txt)

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<div class="feature-source-note"><span class="feature-edition-badge">Beta 1</span><span><strong>Source pages:</strong> PDF 60-61</span><span><a href="https://github.com/nori-shinoda/documents/blob/1773200c5362476c4a549222b7d17fa91f546cae/postgresql10_beta1_new_features_en_20170522-1.pdf">Original PDF on GitHub</a></span></div>

<p class="feature-page-marker" id="pgfeat-10-synchronous-pdf-page-60">PDF page 60</p>

In PostgreSQL 9.5 and earlier, only one instance was available for synchronous replication. In PostgreSQL 9.6, synchronous replication can be performed on multiple instances. PostgreSQL 10 implements Quorum-based synchronous replication, which arbitrarily selects an instance to perform synchronous replication. The synchronous replication environment is set by the synchronous_standby_names configuration parameter as before.

#### Syntax 8 - Up to PostgreSQL 9.5 {#pg10-syntax-8}

```sql
synchronous_standby_names = application_name, application_name, …
```

#### Syntax 9 - PostgreSQL 9.6 {#pg10-syntax-9}

```sql
synchronous_standby_names
=
num_sync
(application_name,
application_name, …)
```

#### Syntax 10 - PostgreSQL 10 {#pg10-syntax-10}

```sql
synchronous_standby_names = FIRST | ANY  num_sync (application_name,
application_name, …)
```

Specifying FIRST or omitting it will have the same behavior as PostgreSQL 9.6. Priorities are determined in the order described in the parameter application_name, and synchronous replication is performed for the number of instances specified by num_sync. If ANY is specified, it will not depend on the order of the instances specified in parameter application_name, and will determine the completion of synchronous replication when WAL is transferred to the slave instance specified by num_sync. If ANY is specified for the configuration parameter synchronous_standby_names, "quorum" is output in the sync_state column of the pg_stat_replication catalog.

<p class="feature-page-marker" id="pgfeat-10-synchronous-pdf-page-61">PDF page 61</p>

**Example 62.** Quorum\-based synchronous replication

```text
postgres=> SHOW synchronous_standby_names ;
        synchronous_standby_names
--------------------------------------
 any 2 (standby1, standby2, standby3)
(1 row)
postgres=> SELECT application_name,sync_state, sync_priority
FROM pg_stat_replication ;
 application_name | sync_state | sync_priority
------------------+------------+---------------
 standby1         | quorum     |             1
 standby2         | quorum     |             1
 standby3         | quorum     |             1
(3 rows)
```