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HDDS-14106. Add -XX:NewRatio=3 to default GC options for CMS #9967

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Merged
adoroszlai merged 2 commits into from
Mar 24, 2026
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HDDS-14106. Add -XX:NewRatio=3 to default GC options for CMS #9967

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9dc337d
Set NewRatio explicitly with ConcurrentMarkSweep GC
rnblough Mar 23, 2026
e7a2037
Merge branch 'apache:master' into HDDS-14106
rnblough Mar 23, 2026
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4 changes: 2 additions & 2 deletions hadoop-ozone/dist/src/shell/ozone/ozone-functions.sh
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Expand Up @@ -1525,8 +1525,8 @@ function ozone_add_default_gc_opts
if [[ ! "$OZONE_OPTS" =~ "-XX" ]] ; then
OZONE_OPTS="${OZONE_OPTS} -XX:ParallelGCThreads=8"
if [[ "$java_major_version" -lt 15 ]]; then
OZONE_OPTS="${OZONE_OPTS} -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=70 -XX:+CMSParallelRemarkEnabled"
ozone_error "No '-XX:...' jvm parameters are set. Adding safer GC settings '-XX:ParallelGCThreads=8 -XX:+UseConcMarkSweepGC -XX:CMSInitiatingOccupancyFraction=70 -XX:+CMSParallelRemarkEnabled' to the OZONE_OPTS"
OZONE_OPTS="${OZONE_OPTS} -XX:+UseConcMarkSweepGC -XX:NewRatio=3 -XX:CMSInitiatingOccupancyFraction=70 -XX:+CMSParallelRemarkEnabled"
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@yandrey321 yandrey321 Mar 23, 2026

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what would be the equivalent for G1GC?

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@rnblough rnblough Mar 23, 2026 •
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Happily there isn't one. The root cause of the problem is an ergonomic detail unique to CMS, from which G1GC does not suffer. This isn't even a bug, it is intended behavior, just from 2004 when there was nothing like modern scale challenges or the individual server resources to meet them.

If we switch to the question of "can G1GC performance be improved with this property" the answer is no as I understand it; G1GC depends on adaptive sizing of the young gen for meeting the pause goals that are set. Any property that fixes the young gen heap size, whether NewRatio, Xmn, or NewSize=MaxNewSize, would stop that mechanism from working. This wouldn't break G1GC, but it would likely mean that we would start consistently exceeding its pause target above some threshold.

ozone_error "No '-XX:...' jvm parameters are set. Adding safer GC settings '-XX:ParallelGCThreads=8 -XX:+UseConcMarkSweepGC -XX:NewRatio=3 -XX:CMSInitiatingOccupancyFraction=70 -XX:+CMSParallelRemarkEnabled' to the OZONE_OPTS"
else
ozone_error "No '-XX:...' jvm parameters are set. Adding safer GC settings '-XX:ParallelGCThreads=8' to the OZONE_OPTS"
fi
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