You can perform following tasks to improve the performance of your alfresco and I hope this might help you..
1. Ask your DBA to re-build indexes and build database statistics (In mysql and postgres this is quite easy).
2. Disable activities feed, I mean you can ignore alfresco activities feeds which are not required and necessary (record limited activities) like below in alfresco-global.properties file
3. Do not run alfresco activities.feed.cleaner job by default which runs every 15 minutes, this causes database performance issues due to more frequent delete of data, you can schedule it to run every night and have the database script to reindex this table every day after delete.
activities.feed.cleaner.cronExpression=0 0 1 * * ?
Insert in to database is never a problem but delete always takes time, indexes need to be rebuild.
4. if you have enabled alfresco audit then do not record all the event and you should customize it to record limit number of events
5. Push all the schedule job in night like ldap sync,solr index backup, custom schedule job if any and you can.
6. Configure the schedule job to delete the user's trashcan after 90 days which will deletes lots of records form database.