I set up system copying all mails to a backup system.
This used to work without a hitch - now in the last few days mails would pile up in the Postfix Queue, waiting to be delivered using the lmtp transport into dovecot.
So dovecot was being slow, but why? After all, nothing changed.
After reading some articles on stackoverflow I found a way of finding out which file gets the most IO:
% sysdig -c topfiles_bytes;
This command quickly pointed to ~/mdbox/mailboxes/INBOX/dbox-Mails/dovecot.index.tmp That file was written excessively.
I then put ~/mdbox/mailboxes/INBOX/dbox-Mails/ into tmpfs and alas, the queue would drain quickly.
But why is that? Why would the index file be updated so often?
This is dovecot 2.3.7.2-1~bionic
# 2.3.7.2 (3c910f64b): /etc/dovecot/dovecot.conf # OS: Linux 5.0.0-29-generic x86_64 Ubuntu 18.04.3 LTS default_vsz_limit = 2 G lmtp_user_concurrency_limit = 10000 mail_attachment_dir = /home/copymail/attachments mail_attachment_hash = %{sha256} mail_fsync = never mail_location = mdbox:~/mdbox mail_plugins = zlib fts fts_lucene mdbox_rotate_size = 128 M namespace inbox { inbox = yes location = mailbox Drafts { special_use = \Drafts } mailbox Junk { special_use = \Junk } mailbox Sent { special_use = \Sent } mailbox "Sent Messages" { special_use = \Sent } mailbox Trash { special_use = \Trash } prefix = } passdb { args = username_format=%u /etc/dovecot/passwd driver = passwd-file } plugin { fts = lucene fts_languages = de,en fts_lucene = whitespace_chars=@. } protocols = " imap lmtp" service imap-login { inet_listener imap { address = 127.0.0.1 port = 143 } inet_listener imaps { port = 993 ssl = yes } } service lmtp { inet_listener lmtp { address = 10.0.5.208 port = 1025 } process_min_avail = 5 unix_listener /var/spool/postfix/private/dovecot-lmtp { group = postfix mode = 0660 user = postfix } } ssl_ca = /etc/ssl/certs/ca-certificates.crt ssl_cert =
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