Description of problem:

nagle is enabled by default. To prevent returned search entries/result to be stuck the server set/reset (setsocketopt) TCP_CORK. It can give a network benefit in term of transmitted overhead, but the cost is a big use of systemcall setsocketopt.

The benefit of nagle should be limited by the fact that DS always write complete PDU (response or entries)

Switching on/off nagle has no significant impact on throughput but gives benefit in terms of syscall

tracing: perf trace -t <worker> -s

NAGLE: off

 ns-slapd (108026), 1527476 events, 100.0%

   syscall            calls    total       min       avg       max      stddev
                               (msec)    (msec)    (msec)    (msec)        (%)
   --------------- -------- --------- --------- --------- ---------     ------
   futex             328122  3059.967     0.000     0.009   360.607     19.06%
   poll              124478   854.697     0.002     0.007   100.142     20.29%
   sendto            124149   785.173     0.002     0.006     0.041      0.11%
   write             123627   483.753     0.002     0.004     0.080      0.10%
   recvfrom           62295   245.209     0.002     0.004     0.040      0.12%
   madvise                9     0.211     0.016     0.023     0.042     12.46%
   sched_yield           34     0.146     0.004     0.004     0.005      1.32%



NAGLE: on
 ns-slapd (108026), 1784094 events, 100.0%

   syscall            calls    total       min       avg       max      stddev
                               (msec)    (msec)    (msec)    (msec)        (%)
   --------------- -------- --------- --------- --------- ---------     ------
   futex             328704  3054.546     0.000     0.009   346.687     17.23%
   setsockopt        124702   656.760     0.001     0.005     0.034      0.14%
   poll              125437   655.709     0.002     0.005   100.141     15.28%
   sendto            124501   464.307     0.001     0.004     0.039      0.14%
   write             125026   462.438     0.001     0.004     0.031      0.10%
   recvfrom           62799   248.383     0.002     0.004     0.030      0.11%
   madvise                3     0.066     0.014     0.022     0.034     26.97%
   sched_yield           10     0.043     0.004     0.004     0.004      1.69%

Version-Release number of selected component (if applicable):


How reproducible:
Will be described later

Actual results:
With searchrate, we can see as much setsockopt than the #write

Expected results:
See lower number of setsockopt