Full vs. incremental updates

[Renate]

Ok, most of you all know this stuff, but just to restate the obvious.

A full update has all (most) of the system stuff you need on your device to run.
It makes no presumptions of what system data you currently have on your device.
On the other hand, it can refuse to update to an older version.
On Onyx a full update is about 1.5 GB or so.

An incremental update contains modifications to existing sytem data on your device.
It presumes that it is modifying a specific, known, last installed, full version.
If you have modified anything by rooting or hacking there may be complications.
On Onyx an incremental update is about 0.5 GB or so.

To make things a bit more complicated, a single update may be partially full and partially incremental.

As an example, here is the last Poke5P full update:

boot             REPLACE, REPLACE_BZ, REPLACE_XZ
dtbo             REPLACE_BZ, REPLACE_XZ
product          REPLACE, REPLACE_BZ, REPLACE_XZ
system           REPLACE, REPLACE_BZ, REPLACE_XZ
system_ext       REPLACE, REPLACE_BZ, REPLACE_XZ
vbmeta           REPLACE_XZ
vbmeta_system    REPLACE_XZ
vendor           REPLACE, REPLACE_BZ, REPLACE_XZ
xbl              REPLACE_XZ

You can see that it does not contain every single partition.
But the ones that it does have, it fully overwrites.
If you replaced the boot image for Magisk you won't have root afterwards, but it won't explode.

Here is a Poke5P incremental update:

abl              REPLACE_XZ
boot             SOURCE_COPY, ZERO, PUFFDIFF, BROTLI_BSDIFF (incremental)
dtbo             ZERO, BROTLI_BSDIFF (incremental)
product          REPLACE_BZ, SOURCE_COPY, ZERO, REPLACE_XZ, PUFFDIFF, BROTLI_BSDIFF (incremental)
recovery         REPLACE, REPLACE_BZ, ZERO, REPLACE_XZ
system           REPLACE_BZ, SOURCE_COPY, ZERO, REPLACE_XZ, PUFFDIFF, BROTLI_BSDIFF (incremental)
system_ext       REPLACE_BZ, SOURCE_COPY, ZERO, REPLACE_XZ, PUFFDIFF, BROTLI_BSDIFF (incremental)
vbmeta           BROTLI_BSDIFF (incremental)
vbmeta_system    BROTLI_BSDIFF (incremental)
vendor           SOURCE_COPY, ZERO, BROTLI_BSDIFF (incremental)
xbl              SOURCE_COPY, ZERO, REPLACE_XZ (incremental)

It modifies lots of things and if those things aren't how it expects there are going to be problems.
Note that abl is fully replaced. If you were looking just for that you could use a payload dumper and get a clean copy.
The other files, like boot, can not be extracted except in the context of a device updated to a specific full update.

(These printouts are from a work-in-progress utility.)