hi,

Does anybody know what can change between .13 ( STAT version 1.4.13, STAT 
libevent 1.4.13-stable) and  .21 (STAT version 1.4.21 STAT libevent 
2.0.21-stable)?

memcached became about 15-20% slower.  We discovered this in production but 
there are too many moving parts. So I used twemperf 
(https://github.com/twitter/twemperf) to measure on dev server


result for .13 (repeated many times)

[dsamoylov.dev twemperf (master)]$ src/mcperf --linger=0 --call-rate=0 
--num-calls=100000 --conn-rate=0 --num-conns=1 --sizes=d1

Total: connections 1 requests 100000 responses 100000 test-duration 9.731 s 
(10.160 s, 9.981 s)

Connection rate: 0.1 conn/s (9731.1 ms/conn <= 1 concurrent connections)
Connection time [ms]: avg 9731.1 min 9731.1 max 9731.1 stddev 0.00
Connect time [ms]: avg 0.2 min 0.2 max 0.2 stddev 0.00

Request rate: 10276.3 req/s (0.1 ms/req)
Request size [B]: avg 28.0 min 28.0 max 28.0 stddev 0.00

Response rate: 10276.3 rsp/s (0.1 ms/rsp)
Response size [B]: avg 8.0 min 8.0 max 8.0 stddev 0.00
Response time [ms]: avg 0.1 min 0.0 max 18.0 stddev 0.00
Response time [ms]: p25 1.0 p50 1.0 p75 1.0
Response time [ms]: p95 1.0 p99 1.0 p999 4.0
Response type: stored 100000 not_stored 0 exists 0 not_found 0
Response type: num 0 deleted 0 end 0 value 0
Response type: error 0 client_error 0 server_error 0

Errors: total 0 client-timo 0 socket-timo 0 connrefused 0 connreset 0
Errors: fd-unavail 0 ftab-full 0 addrunavail 0 other 0

CPU time [s]: user 1.18 system 3.50 (user 12.2% system 36.0% total 48.2%)
Net I/O: bytes 3.4 MB rate 361.3 KB/s (3.0*10^6 bps)


result for .21 (repeated many times)
[dsamoylov.dev twemperf (master)]$ src/mcperf --linger=0 --call-rate=0 
--num-calls=100000 --conn-rate=0 --num-conns=1 --sizes=d1

Total: connections 1 requests 100000 responses 100000 test-duration 12.328 
s (11.230 s, 12.713 s)

Connection rate: 0.1 conn/s (12328.4 ms/conn <= 1 concurrent connections)
Connection time [ms]: avg 12328.4 min 12328.4 max 12328.4 stddev 0.00
Connect time [ms]: avg 0.3 min 0.3 max 0.3 stddev 0.00

Request rate: 8111.4 req/s (0.1 ms/req)
Request size [B]: avg 28.0 min 28.0 max 28.0 stddev 0.00

Response rate: 8111.4 rsp/s (0.1 ms/rsp)
Response size [B]: avg 8.0 min 8.0 max 8.0 stddev 0.00
Response time [ms]: avg 0.1 min 0.0 max 28.3 stddev 0.00
Response time [ms]: p25 1.0 p50 1.0 p75 1.0
Response time [ms]: p95 1.0 p99 1.0 p999 5.0
Response type: stored 100000 not_stored 0 exists 0 not_found 0
Response type: num 0 deleted 0 end 0 value 0
Response type: error 0 client_error 0 server_error 0

Errors: total 0 client-timo 0 socket-timo 0 connrefused 0 connreset 0
Errors: fd-unavail 0 ftab-full 0 addrunavail 0 other 0

CPU time [s]: user 3.38 system 7.44 (user 27.4% system 60.3% total 87.7%)
Net I/O: bytes 3.4 MB rate 285.2 KB/s (2.3*10^6 bps)

same server is used, clean just restarted memcached daemon.

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