Problem Definition

Jira 8.13.x has PostgresSQL driver version 42.2.6. This version has a bug regarding socketTimeout parameter (see https://github.com/pgjdbc/pgjdbc/pull/1831)

This is fixed in Version 42.2.15 (2020-08-14). Please search for 'Make sure socketTimeout is enforced PR 1831 210b27a6' at https://jdbc.postgresql.org/documentation/changelog.html#version_42.2.0

Suggested Solution

Upgrade bundled PostgresSQL JDBC driver to 42.2.16+ version

Note on fix

Staring from Jira 8.16.0 we introduced additional PostgresJdbcConnectionHealthCheck which suggests adding "tcpKeepAlive=true and socketTimeout" parameters and generates the warning in case they are not present:
"We've detected that your Jira instance is not using optimal PostgreSQL JDBC configuration"

See related KB: Connection problems to PostgreSQL result in stuck threads in Jira

Workaround

Upgrade driver manually