I am facing issues with Apache Solr and Dovecot. Everything is working fine and the email messages are indexed correctly but randomly (especially during the night, when in general the email traffic is more relaxed, but also during the day) the Solr server has a high cpu load and a very high I/O activity which leads to slow down the queries to Solr so much that the users receive a timeout during the search in their mailboxes and also during message write (append to the mailbox).

This is my configuration:

• Solr 7.7.3 on CentOS 7
• Dovecot 2.3.18 on CentOS 7
• /var/solr is around 250GB
• The Solr server has 40GB of ram / 2GB of swap (not used).
• SOLR_HEAP="30240m"
• Dovecot is configured with "fts_autoindex = yes"

The solr-config and solr-schema are taken from the Dovecot public repository:

https://raw.githubusercontent.com/dovecot/core/master/doc/solr-schema-7.7.0.xml https://raw.githubusercontent.com/dovecot/core/master/doc/solr-config-7.7.0.xml

I followed the official Dovecot guide here: https://doc.dovecot.org/configuration_manual/fts/solr/

In the Solr logs I don't see any particular/strange behavior when the problem occur.

Probably there is something to tune, but I honestly don't know what to change for my specific configuration.

Can you help me?