docs: disclaim write load for agent metadata (#7048)

ammario · matifali · web-flow · commit 285646bf247f · 2023-04-16T05:46:04.000Z
* docs: disclaim write load for agent metadata

* Update docs/templates/agent-metadata.md

Co-authored-by: Muhammad Atif Ali &lt;atif@coder.com&gt;

* Update docs/templates/agent-metadata.md

Co-authored-by: Muhammad Atif Ali &lt;atif@coder.com&gt;

---------

Co-authored-by: Muhammad Atif Ali &lt;atif@coder.com&gt;
diff --git a/docs/templates/agent-metadata.md b/docs/templates/agent-metadata.md
@@ -70,7 +70,7 @@ resource "coder_agent" "main" {
 distributions and provides virtual memory, CPU and IO statistics. Running `top`
 produces output that looks like:
 
-```
+```text
 %Cpu(s): 65.8 us,  4.4 sy,  0.0 ni, 29.3 id,  0.3 wa,  0.0 hi,  0.2 si,  0.0 st
 MiB Mem :  16009.0 total,    493.7 free,   4624.8 used,  10890.5 buff/cache
 MiB Swap:      0.0 total,      0.0 free,      0.0 used.  11021.3 avail Mem
@@ -80,7 +80,7 @@ MiB Swap:      0.0 total,      0.0 free,      0.0 used.  11021.3 avail Mem
 distributions and provides virtual memory, CPU and IO statistics. Running `vmstat`
 produces output that looks like:
 
-```
+```text
 procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 0  0  19580 4781680 12133692 217646944    0    2     4    32    1    0  1  1 98  0  0
@@ -91,8 +91,29 @@ than `vmstat` but often not included in base images. It is easily installed by
 most package managers under the name `dstat`. The output of running `dstat 1 1` looks
 like:
 
-```
+```text
 --total-cpu-usage-- -dsk/total- -net/total- ---paging-- ---system--
 usr sys idl wai stl| read  writ| recv  send|  in   out | int   csw
 1   1  98   0   0|3422k   25M|   0     0 | 153k  904k| 123k  174k
 ```
+
+## DB Write Load
+
+Agent metadata can generate a significant write load and overwhelm your
+database if you're not careful. The approximate writes per second can be
+calculated using the formula:
+
+```text
+(metadata_count * num_running_agents * 2) / metadata_avg_interval
+```
+
+For example, let's say you have
+
+- 10 running agents
+- each with 6 metadata snippets
+- with an average interval of 4 seconds
+
+You can expect `(10 * 6 * 2) / 4` or 30 writes per second.
+
+One of the writes is to the `UNLOGGED` `workspace_agent_metadata` table and
+the other to the `NOTIFY` query that enables live stats streaming in the UI.
