H2 VS Flyway

The URL should point to a particular comment, but HN removes fragments: https://github.com/h2database/h2database/issues/3686#issueco...

This sounds very much like the idiocy of "infosec" lunkheads who know nothing about what they're "fixing" but if an automated system tells them a CVE exists, they've absolutely got to have it "patched". They don't look into what the claims of the CVE are, or whether their specific use case is vulnerable. They don't know, they don't care, they're not even programmers. All they know is a box needs ticking.

A similar thing happened with h2database - a "security researcher" found that if you do something you're told not to do, then bad things happen.. but they demanded and got a CVE allocated anyway. Anyone who looks at it realises it's bullshit, but the mere existence of a CVE is all that matters to these idiots.

What the h2database developer said about it: https://github.com/h2database/h2database/issues/3686#issueco...

> I struggle to understand why I should feel the slightest shred of sympathy for "major corporations" that are using a volunteer-developed open-source project. Feel free to get your corporation to pay someone to deal with this, or pay for a similar commercial library.

> ...than it would be to learn the exact syntax and quirks and possibly bugs of someone else's implementation...

Yup. Also, having deep knowledge of the language is required.

SQLite's grammar is neat. Creating a compatible parser would make a fun project. Here's a pretty good example: https://github.com/bkiers/sqlite-parser (Actual ANTLR 4 grammar: https://github.com/bkiers/sqlite-parser/blob/master/src/main... )

Postgres, which tries to be compliant with the latest standards, however...

SQL-2016 is a beast. Not to mention all the dialects.

I'm updating my personal (soon to be FOSS) grammar from ANTLR 3 LL(k) to ANTLR 4 ALL().

I've long had a working knowledge of SQL-92, with some SQL-1999 (eg common table expressions).

But the new structures and extensions are a bit overwhelming.

Fortunately, ANTLR project has ~dozen FOSS grammars to learn from. https://github.com/antlr/grammars-v4/tree/master/sql

They mostly mechanically translate BNFs to LL(k) with some ALL(). Meaning few take advantage of left-recursion. https://github.com/antlr/antlr4/blob/master/doc/left-recursi...

Honestly, I struggled to understand these grammars. Plus, not being conversant with the SQL-2016 was a huge impediment. Just finding a succinct corbis of test cases was a huge hurdle for me.

Fortunately, the H2 Database project is a great resource. https://github.com/h2database/h2database/tree/master/h2/src/...

Now for the exciting conclusion...

My ANTLR grammar which passes all of H2's tests looks nothing like any of the official or product specific BNFs.

Further, I found discrepancy between the product specific BNFs and their implementations.

So a lot of trial & error is required for a "real world" parser. Which would explain why the professional SQL parsing tools charge money.

I still think creating a parser for SQLite is a great project.

H2 - Free, Embedded & Open source

H2 2.1

H2 for mocking relational database connections

It's open-source and written in Java, so you can even create custom procedures and register them straight in your application!

Firstly, let's set up a basic Spring Boot application. We can use the Spring Initializr with Spring Data JPA, H2 Database, Lombok added. H2 Database will provide us with a simple database, and Spring Data JPA will allow us to easily interact with it using Hibernate. Lombok will make it easier to write concise and readable classes.

Sorting chunks by similarity: commonly used tools don't do that. Most archive tools only sort by file type.

I wrote a tool that chunks the data (into variable-sized blocks, to re-sync if there are multiple files that have different length prefixes, but that's another story), and then sorts the chunks by LSH (locality sensitive hash). LSH is used by search engines to detect similar text. It can compress directories that contain multiple version of e.g. source code very well (e.g. trunk, branches). https://github.com/h2database/h2database/blob/master/h2/src/...

I discussed this approach with a researcher in this area in January 2020. AFAIK there is active research in this area, specially to compress DNA sequences. But he also wasn't aware of papers or research in this area for general-purpose data compression.

So, I think this area is largely uncharted. I would be interested (as a hobby side project) to help, if somebody is interested.

Also RedGate, but Flyway has some reasons to recommend it over RedGate Deploy depending on your DBAs/workflows: https://flywaydb.org/

(Though I don't think it is "complete" or "perfect", either.)

EF Migrations are in a really good place now if you like/don't mind C# as a language (and you can easily embed SQL inside the C#, too, but there are benefits to being able to also run high level C# code). With today's tooling you can package your migration "runner application" as a single deployable executable for most platforms. You can build the executable once and run it in all your environments. (The same tool that updates your QA and Staging updates your Prod, testably running the same migrations.) Given the single executable deployable I might even consider using it for projects not themselves written in C#.

There is a bit of tooling needed but is already around. For Java for example I had very good experience with a combination of flyway [1] for migrations, testcontainers [2] for making integration tests as easy as unit tests and querydsl [3] for a query and mapping layer.

[1] https://github.com/flyway/flyway

[2] https://java.testcontainers.org/modules/databases/postgres/

[3] https://github.com/querydsl/querydsl

When software starts using a database, it's advisable to have version control, just as we have Github to control our source code. This is all to be sure about what was executed for that specific version. For Java and Spring boot, we have the Flyway framework that aims to resolve this situation, free of charge.

If you're looking for tools, like https://www.liquibase.com/ or https://flywaydb.org/, which are database-state-based schema migration toolkits - it might be relatively straightforward to build similar ones using Databricks SQL drivers.

Honestly I kind of wish there was a Lukas Eder database migration library. Call it whatever jooq-migration. At least I would have more insight of what is going on (<-- seriously look at the commit history).

This is a 4th option, which should play nice with ArgoCD. The following example runs flyway as a k8s job. The desired migration changes are recorded as files within the chart. This helm chart can be integrated with your application (Using hooks to determine when the migration job is run) or run manually.

By using an opinionated framework within the app/service (like Flyway, Migrate, Diesel, etc). Schema migrations happen on app/service start-up.

Depending on the language or platform there are libraries you can use to manage this, such as Prisma on node and Flyway for Java/JVM.

It's probably overkill but I've used github plus flyway at a couple places in the past which is pretty nice tool for tracking changes to a variety of db's, it's also very helpful if you ever need to replicate a db in a new region/environment.

Flyway