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Load Testing Caching strategies#

What the load test does#

See kzs_loadtest. The general idea is:

  1. For each caching strategy:
  2. flush the document cache
  3. select a subset of doc IDs from the system_schemas database
  4. spawn_monitor N workers
    1. Choose a random doc ID and use {'ok', _} = kz_datamgr:open_cache_doc(<<"system_schemas">>, DocId).
  5. wait for all workers to finish, collecting their run times (or noting if a worker failed).
  6. print results for the caching strategy.

TL;DR#

The various strategies allowed will have different impacts on the local Erlang node and the database cluster.

The table below shows that for N processes accessing a nonexistent key, there will be: - 1..N database requests - 1..N store messages to the cache process - potential for the calling process to crash

Strategy DB operations Store messages Crash
none N N yes
async N N no
stampede 1 1 no
stampede_async N 1 no

Briefly:

  • none: stampedes on a non-existing cache key will result in database calls for every request until the cache is populated. It will also cause mailbox pressure on the cache process as the stores come in from the requests. This can backup / crash the processes requesting the data (due to store being a blocking operation).
  • async: similar to none, stampeding processes will result in database calls for every request. However, the processes won't block waiting for the store to complete. Mailbox pressure will still exist on the cache process.
  • stampede: stampedes on a non-existing cache key will result in a single database request. All other processes will block until that request is populated in the cache. A single store will be put in the cache's mailbox. However, the monitor table will see some activity as each process that blocks on the key writes an entry to the monitor table.
  • stampede_async: stampedes will result in database requests for each process, similar to none and async. However, the store will first try to lock the key; if successful the process will issue the an async store. If the process fails to get the lock, it will ignore storing the value and continue.

Scaled Document ID Results#

35> kzs_loadtest:start(10).
using 1 document IDs
starting none...
  finished in 9ms
  min/mean/max: 6 < 7 < 9 (78)
  percentiles: 8(50) 9(75) 9(90) 9(95) 9(99)
  calls: fetch_doc: 10 store_local: 10
starting async...
  finished in 8ms
  min/mean/max: 6 < 6 < 8 (68)
  percentiles: 7(50) 7(75) 7(90) 8(95) 8(99)
  calls: fetch_doc: 10 store_local_async: 10
starting stampede...
  finished in 4ms
  min/mean/max: 4 < 4 < 4 (40)
  percentiles: 4(50) 4(75) 4(90) 4(95) 4(99)
  calls: fetch_doc: 1 store_local: 1
starting stampede_async...
  finished in 8ms
  min/mean/max: 6 < 6 < 8 (69)
  percentiles: 7(50) 8(75) 8(90) 8(95) 8(99)
  calls: fetch_doc: 10 store_local_async: 1
ok
36> kzs_loadtest:start(100).
using 1 document IDs
starting none...
  finished in 54ms
  min/mean/max: 11 < 35 < 52 (3528)
  percentiles: 35(50) 47(75) 50(90) 51(95) 52(99)
  calls: fetch_doc: 100 store_local: 100
starting async...
  finished in 51ms
  min/mean/max: 8 < 31 < 49 (3175)
  percentiles: 33(50) 39(75) 45(90) 47(95) 48(99)
  calls: fetch_doc: 100 store_local_async: 100
starting stampede...
  finished in 11ms
  min/mean/max: 6 < 7 < 10 (762)
  percentiles: 8(50) 8(75) 9(90) 9(95) 9(99)
  calls: fetch_doc: 1 store_local: 1
starting stampede_async...
  finished in 54ms
  min/mean/max: 12 < 35 < 52 (3524)
  percentiles: 33(50) 43(75) 50(90) 51(95) 51(99)
  calls: fetch_doc: 100 store_local_async: 1
ok
37> kzs_loadtest:start(1000).
using 3 document IDs
starting none...
  finished in 122ms
  min/mean/max: 0 < 14 < 110 (14473)
  percentiles: 1(50) 2(75) 74(90) 91(95) 108(99)
  calls: fetch_doc: 212 store_local: 212
starting async...
  finished in 265ms
  min/mean/max: 0 < 75 < 250 (75566)
  percentiles: 49(50) 151(75) 214(90) 233(95) 242(99)
  calls: fetch_doc: 555 store_local_async: 555
starting stampede...
  finished in 52ms
  min/mean/max: 0 < 9 < 34 (9905)
  percentiles: 7(50) 19(75) 27(90) 29(95) 32(99)
  calls: fetch_doc: 3 store_local: 3
starting stampede_async...
  finished in 225ms
  min/mean/max: 0 < 36 < 197 (36651)
  percentiles: 11(50) 67(75) 106(90) 119(95) 186(99)
  calls: fetch_doc: 510 store_local_async: 3
ok
38> kzs_loadtest:start(10000).
using 30 document IDs
starting none...
  finished in 838ms
  min/mean/max: 0 < 38 < 517 (389602)
  percentiles: 0(50) 1(75) 14(90) 432(95) 467(99)
  calls: fetch_doc: 963 store_local: 963
starting async...
  finished in 410ms
  min/mean/max: 0 < 1 < 127 (15693)
  percentiles: 0(50) 0(75) 0(90) 1(95) 52(99)
  calls: fetch_doc: 284 store_local_async: 284
starting stampede...
  finished in 419ms
  min/mean/max: 0 < 6 < 119 (61304)
  percentiles: 0(50) 0(75) 26(90) 52(95) 83(99)
  calls: fetch_doc: 30 store_local: 30
starting stampede_async...
  finished in 491ms
  min/mean/max: 0 < 4 < 259 (41007)
  percentiles: 0(50) 0(75) 1(90) 29(95) 93(99)
  calls: fetch_doc: 572 store_local_async: 30
ok

Fixed document ID results#

39> kzs_loadtest:start(10).
using 3 document IDs
starting none...
  finished in 9ms
  min/mean/max: 5 < 6 < 8 (65)
  percentiles: 7(50) 7(75) 8(90) 8(95) 8(99)
  calls: fetch_doc: 10 store_local: 10
starting async...
  finished in 7ms
  min/mean/max: 5 < 5 < 7 (57)
  percentiles: 6(50) 6(75) 6(90) 7(95) 7(99)
  calls: fetch_doc: 10 store_local_async: 10
starting stampede...
  finished in 5ms
  min/mean/max: 4 < 4 < 5 (41)
  percentiles: 4(50) 4(75) 4(90) 5(95) 5(99)
  calls: fetch_doc: 3 store_local: 3
starting stampede_async...
  finished in 7ms
  min/mean/max: 4 < 5 < 6 (55)
  percentiles: 6(50) 6(75) 6(90) 6(95) 6(99)
  calls: fetch_doc: 10 store_local_async: 3
ok
40> kzs_loadtest:start(100).
using 3 document IDs
starting none...
  finished in 47ms
  min/mean/max: 13 < 31 < 44 (3134)
  percentiles: 29(50) 39(75) 43(90) 43(95) 44(99)
  calls: fetch_doc: 100 store_local: 100
starting async...
  finished in 45ms
  min/mean/max: 9 < 27 < 41 (2713)
  percentiles: 26(50) 36(75) 39(90) 39(95) 40(99)
  calls: fetch_doc: 100 store_local_async: 100
starting stampede...
  finished in 6ms
  min/mean/max: 3 < 4 < 6 (412)
  percentiles: 4(50) 4(75) 5(90) 5(95) 6(99)
  calls: fetch_doc: 3 store_local: 3
starting stampede_async...
  finished in 44ms
  min/mean/max: 10 < 26 < 41 (2672)
  percentiles: 27(50) 35(75) 38(90) 40(95) 40(99)
  calls: fetch_doc: 100 store_local_async: 3
ok
41> kzs_loadtest:start(1000).
using 3 document IDs
starting none...
  finished in 200ms
  min/mean/max: 0 < 51 < 174 (51773)
  percentiles: 3(50) 117(75) 137(90) 149(95) 170(99)
  calls: fetch_doc: 407 store_local: 407
starting async...
  finished in 229ms
  min/mean/max: 0 < 41 < 202 (41632)
  percentiles: 21(50) 70(75) 99(90) 112(95) 199(99)
  calls: fetch_doc: 550 store_local_async: 550
starting stampede...
  finished in 64ms
  min/mean/max: 0 < 16 < 46 (16796)
  percentiles: 15(50) 31(75) 40(90) 42(95) 43(99)
  calls: fetch_doc: 3 store_local: 3
starting stampede_async...
  finished in 209ms
  min/mean/max: 0 < 37 < 190 (37064)
  percentiles: 5(50) 67(75) 112(90) 128(95) 175(99)
  calls: fetch_doc: 448 store_local_async: 3
ok
42> kzs_loadtest:start(10000).
using 3 document IDs
starting none...
  finished in 208ms
  min/mean/max: 0 < 0 < 83 (3674)
  percentiles: 0(50) 0(75) 0(90) 0(95) 3(99)
  calls: fetch_doc: 62 store_local: 62
starting async...
  finished in 576ms
  min/mean/max: 0 < 4 < 243 (41277)
  percentiles: 0(50) 1(75) 1(90) 29(95) 85(99)
  calls: fetch_doc: 590 store_local_async: 590
starting stampede...
  finished in 381ms
  min/mean/max: 0 < 3 < 70 (31947)
  percentiles: 0(50) 0(75) 1(90) 31(95) 58(99)
  calls: fetch_doc: 3 store_local: 3
starting stampede_async...
  finished in 356ms
  min/mean/max: 0 < 1 < 112 (16907)
  percentiles: 0(50) 0(75) 1(90) 2(95) 64(99)
  calls: fetch_doc: 275 store_local_async: 3
ok