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+Dovecot performance tuning
+==========================
+
+Disk I/O optimization
+---------------------
+
+Usually heavily loaded IMAP and POP3 servers don't use much CPU, but they use
+all the disk I/O they can get. So reducing disk I/O is probably the most useful
+optimization you can do.
+
+ * See <MailLocation.LocalDisk.txt> for generic disk I/O optimizations.
+ * See <MailLocation.Mbox.txt> for mbox-specific optimizations.
+ * See <MailLocation.Maildir.txt> for Maildir-specific optimizations.
+ * See <dbox> [MailboxFormat.dbox.txt] for Dovecot's own high-performance
+   mailbox format. It usually gives much better performance than mbox/Maildir.
+ * See <full text search indexes> [Plugins.FTS.txt] for optimizing IMAP SEARCH
+   command.
+ * See <POP3Server.txt> for POP3 optimizations, especially
+   'pop3_no_flag_updates=yes'
+ * 'mailbox_list_index=yes' can help a lot by replying to IMAP STATUS (and
+   similar) lookups from a single index without having to open each mailbox
+   index separately. This is the default in v2.3+.
+    * Also 'mailbox_list_index_very_dirty_syncs=yes' makes Dovecot assume that
+      the list index is up-to-date.
+ * 'mail_prefetch_count' setting may be helpful with some mailbox formats
+ * 'mail_location = ...:VOLATILEDIR=/tmp/dovecot-volatile/%2.256Nu/%u' moves
+   e.g. lock files to the volatile directory. This is helpful especially if
+   mail_location otherwise points to a remote filesystem like NFS. (v2.2.32+)
+ * If acl plugin is used, but only global ACLs are needed, set
+   'acl_globals_only=yes' (v2.2.31+)
+
+CPU usage optimization
+----------------------
+
+ * See <LoginProcess.txt> for optimizing CPU usage caused by logins
+ * See 'auth_cache_size' setting for caching passdb and userdb lookups
+    * To distribute password hash calculations to multiple CPU cores (via
+      auth-worker processes), set 'auth_cache_verify_password_with_worker=yes'
+      (v2.2.34+)
+ * Services having client_limit>1 and process_limit>1, set process_min_avail to
+   the number of CPU cores
+ * To reduce forks by reusing existing processes for new requests increase
+   'service { service_count }' from 1 to higher (e.g. 100) for imap and pop3
+   services. It's better not to set it too high or unlimited (0), because
+   different users use different amounts of memory, and it's wasteful when a
+   lot of processes end up having a lot of "free" memory.
+
+Memory usage optimization
+-------------------------
+
+There aren't many settings which affect Dovecot's memory usage. In general
+Dovecot uses as much memory as it needs, which is usually quite little.
+
+ * 'auth_cache_size' controls maximum memory size for caching passdb/userdb
+   lookups
+ * <High-performance mode for login processes> [LoginProcess.txt].
+ * 'imap_hibernate_timeout' controls when to move IDLEing IMAP connections to
+   wait for changes in a shared imap-hibernate process. This frees up the imap
+   process.
+
+Note that these settings do not directly affect the memory usage:
+
+ * 'service { vsz_limit } ': These are simply safe guards against potential
+   memory leaks. If the process's virtual size reaches the limit, the process
+   is killed by the kernel.
+ * 'service { process_limit, client_limit } ': These are mostly to avoid DoS
+   attacks using up all your memory.
+
+(This file was created from the wiki on 2019-06-19 12:42)