add some docs for #20

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NatureFreshMilk 2019-03-19 08:21:47 +01:00
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# Incremental rendering
Incremental rendering works with the help of the *mtime* column
on the minetest database.
Every insert or update changes the *mtime* column to the current timestamp (with the help of triggers).
This way changes to the blocks can be detected by remembering the mtime of the
last query.
## Table *blocks* (minetest db)
posx | posy | posz | data | mtime
--- | --- | --- | --- |
10 | 11 | 12 | ABC | 1552977950000
20 | 21 | 22 | 123 | 1552977950010
30 | 31 | 32 | XYZ | **1552977950020**
40 | 41 | 42 | A12 | 1552977950030
50 | 51 | 52 | B34 | 1552977950040
## Table *settings* (mapserver db)
key | value
--- |
last\_mtime | **1552977950020**
## Query example
The following query will return all changed blocks since the last call:
```
select posx,posy,posz,data,mtime
from blocks b
where b.mtime > 1552977950020
order by b.mtime asc
limit 1000
```
Additionally it will limit the returned rows so the mapserver can be started and stopped at any time
without processing all new data at once.
After that query the highest *mtime* is stored again in the mapserver database.
## Schedule
Incremental rendering is executed periodically:
* Without pause between calls if there is more data available (catch-up after mapserver downtime)
* With a 5 second pause between calls if there is no new data
## About realtime
Of course there are delays between placing/removing blocks and the tiles on the mapserver.
The minetest setting ** server\_map\_save\_interval ** is responsible for the delay to the mapserver (defaults to 5.3 seconds)
Don't try to decrease this value too much on your minetest instance, it has a performance impact!

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* [License](doc/license.md)
* [Changelog](doc/changelog.md)
# How it works
See: [Incremental rendering](doc/incrementalrendering.md)
# Compatibility
* Minetest 0.4.15 - 0.4.17.1