How many pool connection size should be set for a 1000 users Jira system?

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For a Jira system, if use Jira's default connection configuration as below:

<?xml version="1.0" encoding="UTF-8"?>

<jira-database-config>
<name>defaultDS</name>
<delegator-name>default</delegator-name>
<database-type>postgres72</database-type>
<schema-name>public</schema-name>
<jdbc-datasource>
<url>jdbc:postgresql://[IP]:5432/jiradb</url>
<driver-class>org.postgresql.Driver</driver-class>
<username>jiradbuser</username>
<password>{PASSWORD}</password>
<pool-min-size>20</pool-min-size>
<pool-max-size>20</pool-max-size>
<pool-max-wait>30000</pool-max-wait>
<validation-query>select 1</validation-query>
<min-evictable-idle-time-millis>60000</min-evictable-idle-time-millis>
<time-between-eviction-runs-millis>300000</time-between-eviction-runs-millis>
<pool-max-idle>20</pool-max-idle>
<pool-remove-abandoned>true</pool-remove-abandoned>
<pool-remove-abandoned-timeout>300</pool-remove-abandoned-timeout>
<pool-test-on-borrow>false</pool-test-on-borrow>
<pool-test-while-idle>true</pool-test-while-idle>
</jdbc-datasource>
</jira-database-config>

In postgresql's config file:

postgresql.conf

```
max_connections = 300
shared_buffers = 80MB
```

In /etc/sysctl.conf file:

```
kernel.shmmax=100663296
```

At test stage, it can work. But in the production environment, for 1000 users use this system, if one app server serve 500 users, how many pool connection size is good to set in the postgresql.conf file?
And, if use pgbouncer, how many connections it can be reduced?