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construct/doc/TUNING.md

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## TUNING
This guide is intended for system administrators to optimize Construct and
maximize its performance for their environment. This does not cover [BUILD](BUILD.md)
tuning, and it is expected that Construct is already installed and the [SETUP](SETUP.md)
has been completed.
- Some instructions may reference Construct's configuration system. This is
accessed via the administrator's console which can be reached by striking
`ctrl-c (SIGINT)` and then using the `conf` command (see: `help conf`). The
console can also be reached interactively through your preferred client in
the `!control` room. Alternatively, configuration state can be manipulated
directly through the `!conf` room. Configuration changes take effect as a
result of state events sent to the `!conf` room, thus all aforementioned
methods to change configuration are the same.
- CHANGES TO CONFIGURATION ARE EFFECTIVE IMMEDIATELY. ERRONEOUS VALUES MAY
CAUSE UNEXPECTED BEHAVIOR AND RESULT IN PROGRAM TERMINATION. CONFIGURATION
ERRORS MAY ALSO PREVENT STARTUP. Please see the
[TROUBLESHOOTING](TROUBLESHOOTING.md#recovering-from-broken-configurations)
guide for how to recover from configuration errors.
### Event Cache Tuning
Most of Construct's runtime footprint in RAM consists of a cache of Matrix
events read from the database. The data in many of these events may be
directly accessed for fundamental server operations; for example, a client's
access-token and user information is stored with events in special server
rooms. The event cache is a set of LRU (Least Recently Used) caches. The size
of these caches should be tuned to at least the "working-set size" expected
by the server. If these caches are too small, load will be placed
on the next storage tier. For storage devices with poor random access
characteristics it is important these caches cover the server's working-set
size.
To list the event cache information, try the following commands (example output
shown):
```
> db cache events *
COLUMN PCT HITS MISSES INSERT CACHED CAPACITY INSERT TOTAL LOCKED
* 61.94% 18742243 3818637 3814446 1.41 GiB (1517280856) 2.28 GiB (2449473536) 4.46 GiB (4787594200) 4.41 MiB (4628512)
```
```
> db cache events **
COLUMN PCT HITS MISSES INSERT CACHED CAPACITY INSERT TOTAL LOCKED
content 17.85% 2113271 85256 83255 22.85 MiB (23962992) 128.00 MiB (134217728) 569.37 MiB (597026848) 0.00 B (0)
depth 90.71% 11292 96431 96431 58.06 MiB (60876968) 64.00 MiB (67108864) 59.68 MiB (62575248) 0.00 B (0)
event_id 9.24% 191518 153523 153523 5.92 MiB (6202768) 64.00 MiB (67108864) 865.07 MiB (907093240) 0.00 B (0)
origin_server_ts 99.99% 9852 566483 566258 64.00 MiB (67103832) 64.00 MiB (67108864) 353.29 MiB (370455584) 0.00 B (0)
room_id 99.99% 1015939 216695 216694 63.99 MiB (67102496) 64.00 MiB (67108864) 132.05 MiB (138467768) 1.93 MiB (2019088)
sender 39.18% 56357 80879 80879 50.16 MiB (52592768) 128.00 MiB (134217728) 50.36 MiB (52809616) 0.00 B (0)
state_key 40.49% 7336 89035 87181 25.91 MiB (27171856) 64.00 MiB (67108864) 383.42 MiB (402049648) 0.00 B (0)
type 99.92% 1716885 66485 66485 31.97 MiB (33527264) 32.00 MiB (33554432) 40.69 MiB (42667312) 0.00 B (0)
_event_idx 99.99% 652575 505956 505955 255.98 MiB (268418416) 256.00 MiB (268435456) 635.40 MiB (666268064) 23.45 KiB (24016)
_room_events 62.14% 308312 13144 13144 79.54 MiB (83405864) 128.00 MiB (134217728) 79.73 MiB (83608112) 284.73 KiB (291560)
_room_joined 52.73% 2087968 6789 6789 4.22 MiB (4422936) 8.00 MiB (8388608) 4.23 MiB (4431280) 0.00 B (0)
_room_state 25.40% 2038549 21590 21590 16.25 MiB (17044504) 64.00 MiB (67108864) 52.26 MiB (54793600) 0.00 B (0)
_room_head 26.41% 7986 9435 9435 2.11 MiB (2215192) 8.00 MiB (8388608) 37.56 MiB (39389688) 0.00 B (0)
_event_json 62.79% 82254 1166164 1166153 642.96 MiB (674189112) 1024.00 MiB (1073741824) 736.76 MiB (772552224) 3.52 MiB (3690824)
_event_refs 79.17% 54501 112508 112505 50.67 MiB (53127080) 64.00 MiB (67108864) 68.76 MiB (72098088) 0.00 B (0)
_event_type 99.77% 22 8215 8215 15.96 MiB (16738848) 16.00 MiB (16777216) 17.27 MiB (18109240) 73.93 KiB (75704)
_event_sender 0.00% 0 23453 23453 0.00 B (0) 16.00 MiB (16777216) 15.01 MiB (15739768) 0.00 B (0)
_event_horizon 99.96% 15722 18296 18296 15.99 MiB (16769768) 16.00 MiB (16777216) 18.91 MiB (19833200) 0.00 B (0)
_room_state_space 67.24% 3997 24712 24712 86.06 MiB (90241400) 128.00 MiB (134217728) 92.28 MiB (96762256) 0.00 B (0)
```
To view the configuration item for the size of a cache, which should match your
output from the above command, use the following command where `<COLUMN>` is
replaced by one of the names under `COLUMN` in the above output:
```
conf ircd.m.dbs.events.<COLUMN>.cache.size
```
To alter a cache size, set the configuration item with a byte value. In the
example below we will set the `_event_json` cache size to 256 MiB. This change
will take effect immediately and the cache will grow or shrink to that size.
```
conf set ircd.m.dbs.events._event_json.cache.size 268435456
```
> Tip: The best metric to figure out which caches are inadequate is not
necessarily the utilization percentage. Caches that are too small generally
exhibit high values under `INSERT TOTAL` as well as full utilization. If this
value is several times higher than the cache size and growing, consider
increasing that cache's size.
### Client Pool Tuning
(TODO)