So just to give an insight of the currently faced issues: We tried updating a large Limesurvey system (DB size: 4.5GB) from 1.92 to the latest 3.21.2 version and totally failed. We wasted some hours trying to debug errors before going from version to version in small steps which finally worked fine.

This is what happened:

1. Test: Updating directly to 3.21.2
   -> Error when updating DB: "Alias "application.helpers.expressions.warnings.EMWarningInvalidComparison" is invalid.", see bug report at https://bugs.limesurvey.org/view.php?id=15677. Not sure if this is a different issue.

2. Test: Use the previous 3.20.0 version (also test 3.19)
   -> Error: Table {{permissions}} for ActiveRecord class "Permission" not found at DB. That's true since the "permissions" table didn't exist at 1.92. But the updater didn't notice that, though special updating code is there at https://github.com/LimeSurvey/LimeSurvey/blob/c0c0c6e9abaaf2f59f0b22aea2409d618b690b9d/application/helpers/update/updatedb_helper.php#L1018.

3. Test: Try an older 2.73 version
   -> Same issues as #2 above

4. Test: Try an older 2.05 version
   -> Same issues as #2 above

5. Test: Test with 2.00
   -> Finally, the DB updater was able to update to DB version 164

6. Go from 2.00 to 2.05
   -> The updater worked fine and created the new permission table when updating to DB version 178

7. Go from 2.05 to 2.73
   -> Updated to DB version 263

8. Go from 2.73 to 3.19
   -> Updated to DB version 359

9. Lastly, we updated from 3.19 to 3.21.2 using ComfortUpdate

That took several hours including yelling at the PC and searching documentation for possible solutions.

Assuming that there will be huge DB adjustments when going from LS 4 to LS 5 (more object oriented question models, new DB schema for strong responses in a non-flat-table system, ...) we should find better ways to run such updates.

Feel free to ping us/David if you want to discuss using Yii migration classes.

@DenisChenu, have you ever faced similar problems when updating stone-old systems?

What do you suggest to provide better updating features?

Error: Table {{permissions}} for ActiveRecord class "Permission" not found at DB

I think it was managed in previous system ?

What do you suggest to provide better updating features?

I already say we need update $to : then we can upgrade really step by step.

Using Yii system seem great too, but REALLY need more work (we need to create whole update system from 1.80 …)

Test: Updating directly to 3.21.2

Did you clear cache after update?

@ollehar: I do not really remember if I cleared the cache but at other updates I noticed that not clearing cache can indeed cause weird issues like being unable to log in.

@Mazi, to be precise, I'm talking about the Yii runtime cache. Hm, wait, I remember someone else talking about that problem. Strange.

This won't be implemented.
We introduced recently proper classes for each upgrade step.