# How to speed up the segment merging
**URL:** https://discuss.elastic.co/t/how-to-speed-up-the-segment-merging/260044
**Category:** Elasticsearch
**Created:** [January 4, 2021, 1:44am UTC](https://discuss.elastic.co/t/how-to-speed-up-the-segment-merging/260044 "2021-01-04T01:44:57Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@chemboking](https://discuss.elastic.co/u/chemboking)
#### Post date: [January 4, 2021, 1:44am UTC](https://discuss.elastic.co/t/how-to-speed-up-the-segment-merging/260044/1 "2021-01-04T01:44:57Z")
I don't understand why merging a 8GB(total) shard into one 3GB segment shard should take about 6 minutes, while all the indicators(io/cpu/memory/gc) of the machine(ssd/32 cores/30GB jvm/64GB total/swap disabled) are very low.
I have tried the following configurations:
- set the thread\_pool.force\_merge.size to 4, I understand that merging is one thread per shard, but there is still one merge thread(through remote debug) after i put two shards in one ES node, and the merging time is twice that of the one shard. What did i miss?
- set the data directory to the /dev/shm, and the process doesn't seem to have changed much.
BTW, here is my scenario(3 ES nodes in 3 machines separately， one index with 6 shards, 0 replica, each machine shall have two shards, ES version 7.7.1)
1. create the index, set the refresh interval to -1
2. bulk into the es
3. stop writing, call refresh and set refresh interval to 60s
4. force merge into 1 segments by calling the \_forcemerge?max\_num\_segments=1
5. wait until the segments become 1 and prepare the alias to take traffic
After merging into 1 segment, the size of the whole index is about 14GB, 2 million docs.
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [February 1, 2021, 1:45am UTC](https://discuss.elastic.co/t/how-to-speed-up-the-segment-merging/260044/2 "2021-02-01T01:45:07Z")
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