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Reduce how much old WAL we keep around. (#7098) 

Previously we were keeping up to around 6 hours of WAL around by
removing 1/3 every hours. This was excessive, so switch to removing 2/3
which will up to around 3 hours of WAL around.

This will roughly halve the size of the WAL and halve startup time for
those who are I/O bound. This may increase the checkpoint size for
those with certain churn patterns, but by much less than we're saving
from the segments.

Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>
This commit is contained in:
Brian Brazil 2020-04-07 11:25:57 +01:00 committed by GitHub
parent 3348930df5
commit cd73b3d33e
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1 changed files with 5 additions and 3 deletions
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8
tsdb/head.go
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@ -681,9 +681,11 @@ func (h *Head) Truncate(mint int64) (err error) {
if last < 0 { if last < 0 {
return nil // no segments yet. return nil // no segments yet.
} }
// The lower third of segments should contain mostly obsolete samples. // The lower two thirds of segments should contain mostly obsolete samples.
// If we have less than three segments, it's not worth checkpointing yet. // If we have less than two segments, it's not worth checkpointing yet.
last = first + (last-first)/3 // With the default 2h blocks, this will keeping up to around 3h worth
// of WAL segments.
last = first + (last-first)*2/3
if last <= first { if last <= first {
return nil return nil
} }