Re: Creating complex track changes database - challenge!

Hi Manual,

thank you very much!

Regarding your  tool - if it is not supported and it is for specific case - i will not use it but figure out something new. I do not even how to install this .hs files...

I thought about creating triggers to have all changes to specific tables. 

And for each table name (or number) keep changes in one separate table. 

What do you think about it? 

If all you need is saving and restoring specific table states, logical dumps with pg_dump should probably be enough for your needs.

Can you explain in details how can i use it? 

What if user add new column? I can save ma table for example as version 3 and come back to version 1 in the future? (without this new column?)

Best,

Jacek 

2018-02-26 12:04 GMT+01:00 Manuel Gómez <targen@gmail.com>:

On Mon, Feb 26, 2018 at 11:44 AM Łukasz Jarych <jaryszek@gmail.com> wrote:

I have to:

1. Keep all changes within table including:

-adding rows

-deleting

-editing

2. Save table with specific state and recover specific state (so go back to previous table versions) including comparing tables.

3. Track all DLL and DML changes with possibility to ho back to previous version.

Hi,

I had similar needs long ago, so I wrote this tool I called Squealer, which would transform a specification of a SQL database schema into some PostgreSQL DDL to create a database that implements the same schema in a logical sense, but actually stores all historical rows, and even permits existing rows to have references to (soft-)deleted rows, all while providing modifiable views that simulate the behavior of a regular table as specified in the input schema through generous use of INSTEAD OF triggers.  It works somewhat like having version control for your database.

You may find the source code here: https://github.com/mgomezch/squealer  Unfortunately, it has hardly any comments, it is completely unmaintained and probably unused anywhere, I have no idea whether it builds with today's libraries, and it does not necessarily break the tradeoffs in this space in a way that fits your use case.

Note there are major caveats with keeping all historical data around forever, and the semantics of querying historical data can get complicated, let alone having current data refer to deleted, historical data.  I built this for a very specific use case where this was the right design, but please consider very carefully whether this is what you want.

Storing your database history forever would take a lot of space.  Consider whether you can instead keep a record of changes stored outside the database in some cheap cold storage.  Also consider just keeping a set of tables with dynamically structured event records (e.g. JSON fields) partitioned by time ranges and retained only temporarily, perhaps even in a separate database.  Any such solution will have significant cost and performance impact if your database bears a nontrivial load, so be careful.

You could also just place your database on a PostgreSQL cluster by itself and then keep all WAL segments archived forever, so you could just do point-in-time recovery to any point in the history of your database.  The space required would grow very quickly, though, so if you don't really need the full history forever, but only a fixed retention period, you can surely use any of the well-known solutions for PostgreSQL backups that allow for this through WAL archiving and periodic basebackups: e.g. WAL-E, WAL-G, pgBackRest…

If all you need is saving and restoring specific table states, logical dumps with pg_dump should probably be enough for your needs.