From 14b3c5bc64a16df07583fe4b5ef2e0129d063893 Mon Sep 17 00:00:00 2001 From: Jeremy Harris Date: Thu, 17 Sep 2015 13:35:16 +0100 Subject: DNS: time-limit cached returns, using TTL. Bug 1395 This can matter for fast-changing data such as DNSBLs. --- doc/doc-docbook/spec.xfpt | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) (limited to 'doc/doc-docbook') diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index 34fbed88f..ed3533a0c 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -6993,6 +6993,15 @@ Retries for the dnsdb lookup can be controlled by a retry modifier. The form if &"retry_VAL"& where VAL is an integer. The default count is set by the main configuration option &%dns_retry%&. +.new +.cindex cacheing "of dns lookup" +.cindex TTL "of dns lookup" +.cindex DNS TTL +Dnsdb lookup results are cached within a single process (and its children). +The cache entry lifetime is limited to the smallest time-to-live (TTL) +value of the set of returned DNS records. +.wen + .section "Pseudo dnsdb record types" "SECID66" .cindex "MX record" "in &(dnsdb)& lookup" @@ -29208,9 +29217,15 @@ deny dnslists = blackholes.mail-abuse.org warn message = X-Warn: sending host is on dialups list dnslists = dialups.mail-abuse.org .endd -DNS list lookups are cached by Exim for the duration of the SMTP session, +.cindex cacheing "of dns lookup" +.cindex DNS TTL +DNS list lookups are cached by Exim for the duration of the SMTP session +.new +(but limited by the DNS return TTL value), +.wen so a lookup based on the IP address is done at most once for any incoming -connection. Exim does not share information between multiple incoming +connection (assuming long-enough TTL). +Exim does not share information between multiple incoming connections (but your local name server cache should be active). -- cgit v1.2.3