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new 603493b Suggest adjust bookkeekper.conf default FlushEntryLogBytes to
256MB to improve bookie io throughput (#6915)
603493b is described below
commit 603493b50b9a53b8f84f837d20b4ee87b60de945
Author: hangc0276 <[email protected]>
AuthorDate: Sat May 9 14:41:00 2020 +0800
Suggest adjust bookkeekper.conf default FlushEntryLogBytes to 256MB to
improve bookie io throughput (#6915)
### Motivation
When AddEntry to bookie, entries will be written to memtable first and then
written to the journal log. If it blocked in memtable write, the total AddEntry
operation will be blocked, and the 99th AddEntry latency will increase.
When memtable full or checkpoint scheduled by timer, memtable will be
swapped with backup one. However, if the backup memtable has not been flushed
to disk complete yet, the memtable swap will be blocked, and the `AddEntry`
operation will be blocked. So in which situation the backup memtable will be
blocked?
When pulsar doing `catch-up read`, large amount of data will be read from
ledger disk, and ledger disk io util will increase. At the same time, backup
memtable will flush data from PageCache to disk triggered by OS (default is
30s) or rolling file no matter for HDD or SSD. It is hard to control the flush
frequency and batch size in each flush cycle. In most cases, the flush batch
size of each flush cycle is from 500MB to 1GB, which will lead to the ledger
disk io util to 100% from 1s [...]
### Changes
In order to decrease ledger disk high io util duration, we can control the
backup memtable flush batch size from pageCache to disk. In my practice, the
flush batch set to 256MB may perform better for HDD disk.
So I suggest adjust the default configuration `FlushEntryLogBytes` to 256MB
in bookkeeper.conf to increase bookie io throughput.
---
conf/bookkeeper.conf | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/conf/bookkeeper.conf b/conf/bookkeeper.conf
index 869a35e..4b17ddc 100644
--- a/conf/bookkeeper.conf
+++ b/conf/bookkeeper.conf
@@ -442,7 +442,7 @@ entryLogFilePreallocationEnabled=true
# happens on log rotation.
# Flushing in smaller chunks but more frequently reduces spikes in disk
# I/O. Flushing too frequently may also affect performance negatively.
-# flushEntrylogBytes=0
+flushEntrylogBytes=268435456
# The number of bytes we should use as capacity for BufferedReadChannel.
Default is 512 bytes.
readBufferSizeBytes=4096
