nickva opened a new pull request, #5:
URL: https://github.com/apache/couchdb-folsom/pull/5
Benchmarking CouchDB in a Kubernetes cluster with lock counting enabled,
noticed `folsom_slide_uniform` ets folsom histogram table locks were at the top
with lot of collisions and time spent waiting on them. Folsom sliding window
histograms add their data using an `ets:insert/2` operation. `ets:insert/2` has
to acquire an ets metadata lock in order to atomically update the ets size and
memory usage. In our case, we don't need to atomically track `ets:info/2` so we
can use the new (since Erlang 23+) `{decentralized_counters, true}` to reduce
some of the lock contention.
```
> lcnt:rt_opt({copy_save, true}), lcnt:clear(), timer:sleep(10000),
lcnt:collect(), lcnt:conflicts().
lock id #tries #collisions collisions [%]
time [us] duration [%]
----- --- ------- ------------ ---------------
---------- -------------
db_hash_slot 2432 3073630 155606 5.0626
80812927 807.3885
run_queue 22 12050789 1823812 15.1344
74547468 744.7913
proc_main 64973 6287153 2020053 32.1299
19640746 196.2274
pix_lock 1024 320419 272 0.0849
3071989 30.6917
proc_status 64973 5666139 92365 1.6301
1792422 17.9078
alcu_allocator 10 1146957 108469 9.4571
1674152 16.7262
dirty_run_queue_sleep_list 2 1920837 276037 14.3707
1355878 13.5464
proc_msgq 64973 7011355 24101 0.3437
78924 0.7885
dist_entry_out_queue 7 367096 1676 0.4566
6023 0.0602
atom_tab 1 4760261 46 0.0010
4167 0.0416
port_sched_lock 101 390590 353 0.0904
1705 0.0170
dist_entry_links 6 23389 14 0.0599
323 0.0032
db_tab 399 4968232 13 0.0003
146 0.0015
drv_ev_state 128 72977 6 0.0082
40 0.0004
```
```
> lcnt:inspect(db_hash_slot).
lock id #tries #collisions collisions [%]
time [us] duration [%] histogram [log2(us)]
----- --- ------- ------------ ---------------
---------- ------------- ---------------------
db_hash_slot folsom_slide_uniform 21808 13020 59.7029
7075598 70.6911 | ............XX. . |
db_hash_slot folsom_slide_uniform 24165 12706 52.5802
6640890 66.3480 | .............XX.. |
db_hash_slot folsom_slide_uniform 25239 10766 42.6562
5779694 57.7440 | ............XX.. |
db_hash_slot folsom_slide_uniform 23089 9987 43.2544
5082403 50.7774 | ............XX... |
db_hash_slot folsom_slide_uniform 23590 9598 40.6867
4994044 49.8947 | .............XX... |
db_hash_slot folsom_slide_uniform 19252 6916 35.9235
4676219 46.7193 | .............Xx.... |
db_hash_slot folsom_slide_uniform 26561 7277 27.3973
4173067 41.6924 | .............XX.. .. |
db_hash_slot folsom_slide_uniform 19250 5136 26.6805
4018223 40.1454 | ............XX.... |
db_hash_slot folsom_slide_uniform 23604 8058 34.1383
3995173 39.9151 | ............XX.. |
db_hash_slot folsom_slide_uniform 22218 4877 21.9507
3647108 36.4376 | ............XX..... |
db_hash_slot folsom_slide_uniform 26549 6959 26.2119
3558691 35.5543 | ............XX... |
db_hash_slot folsom_slide_uniform 22716 6124 26.9590
3097839 30.9500 | ............XX.. |
db_hash_slot folsom_slide_uniform 25615 5936 23.1739
2921810 29.1913 | .............XX. |
db_hash_slot folsom_slide_uniform 26012 5798 22.2897
2853857 28.5124 | ............XX.. |
db_hash_slot folsom_slide_uniform 25615 5137 20.0547
2486628 24.8435 | .............XX. |
db_hash_slot folsom_slide_uniform 27787 4392 15.8060
2110240 21.0831 | ............XX.. |
db_hash_slot folsom_slide_uniform 23168 4041 17.4422
2056501 20.5462 | .............XX. |
db_hash_slot folsom_slide_uniform 21923 3927 17.9127
2055016 20.5313 | ............XX.. |
db_hash_slot folsom_slide_uniform 27816 4092 14.7110
1878684 18.7696 | .............XX. |
db_hash_slot folsom_slide_uniform 26001 3802 14.6225
1774354 17.7273 | ............XX.. |
```
https://www.erlang.org/blog/scalable-ets-counters/
https://www.erlang.org/doc/man/ets.html#new-2
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