From c50a3eccce2e0a26407bf5771cb9e6f83628c05e Mon Sep 17 00:00:00 2001
From: Frederic Branczyk <fbranczyk@gmail.com>
Date: Fri, 12 May 2017 11:48:51 +0200
Subject: [PATCH] prometheus: default max-block-duration to 10% of retention

---
 cmd/prometheus/config.go | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/cmd/prometheus/config.go b/cmd/prometheus/config.go
index a7986b99c..273e09408 100644
--- a/cmd/prometheus/config.go
+++ b/cmd/prometheus/config.go
@@ -134,8 +134,8 @@ func init() {
 		"Minimum duration of a data block before being persisted.",
 	)
 	cfg.fs.DurationVar(
-		&cfg.tsdb.MaxBlockDuration, "storage.tsdb.max-block-duration", 36*time.Hour,
-		"Maximum duration compacted blocks may span.",
+		&cfg.tsdb.MaxBlockDuration, "storage.tsdb.max-block-duration", 0,
+		"Maximum duration compacted blocks may span. (Defaults to 10% of the retention period)",
 	)
 	cfg.fs.IntVar(
 		&cfg.tsdb.AppendableBlocks, "storage.tsdb.appendable-blocks", 2,
@@ -210,6 +210,10 @@ func parse(args []string) error {
 		}
 	}
 
+	if cfg.tsdb.MaxBlockDuration == 0 {
+		cfg.tsdb.MaxBlockDuration = cfg.tsdb.Retention / 10
+	}
+
 	return nil
 }