Work on SQLite4 has concluded

Have you seen an ATM? They're running Windows & SQL Server now. Microsoft isn't offering 35yr support contracts for Windows.

This is only partially sarcastic.

>SQLite License. Warranty of title and perpetual right-to-use for the SQLite source code.

Obtaining A License To Use SQLite

Even though SQLite is in the public domain and does not require a license, some users want to obtain a license anyway. Some reasons for obtaining a license include:

    Your company desires warranty of title and/or indemnity against claims of copyright infringement.
    You are using SQLite in a jurisdiction that does not recognize the public domain.
    You are using SQLite in a jurisdiction that does not recognize the right of an author to dedicate their work to the public domain.
    You want to hold a tangible legal document as evidence that you have the legal right to use and distribute SQLite.
    Your legal department tells you that you have to purchase a license.

If you feel like you really need to purchase a license for SQLite, Hwaci, the company that employs all the developers of SQLite, will sell you one. All proceeds from the sale of SQLite licenses are used to fund continuing improvement and support of SQLite.

How is it possible that they can sell licenses to the code that was put into the public domain by other contributors?

A contributor must attach the following declaration[1] to contribute. So now their contributions are in public domain. Now in a place where the law doesn't recognize public domain, doesn't the code belong to the original authors? How can an unaffiliated company license it as if they wrote the code?

[1]: "The author or authors of this code dedicate any and all copyright interest in this code to the public domain. We make this dedication for the benefit of the public at large and to the detriment of our heirs and successors. We intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this code under copyright law."

I got lucky! It was a class event, and he's known to speak at databases / data systems classes. He's a very fun (and opinionated!) speaker.

> The in-memory tree is an append-only red-black tree structure used to stage user data that has not yet flushed into the database file by the system.

Hmm, ok, so this contradicts my assumption. Actually, now that I think about it, other LSMs like rocksdb / leveldb work like this too (library-like model with some in-memory component when you "open" the database).

Anyway, without diving into the details of the code, there's other technical decisions that would affect this stuff.

One thing is how big your in-memory structure is (in relation to available memory and insertion workload) and how often you flush to disk is a key thing. Another thing is what your LSM tree looks like - aside from the data structure, how many tiers/levels you have is a big thing. I assume some of these are configurable parameters. E.g. rocksdb has an enormous set of parameters that handles this stuff. It's also annoying to tune.

I found this benchmark here that is illustrative: https://sqlite.org/src4/doc/trunk/www/lsmperf.wiki

The first graph is underwhelming, but when you adjust the buffers (look at the last graph) ~250k writes / second constant regardless of database size (this is why you want an LSM tree) is darned good! And this is on a spinny drive, not an SSD. Their "large" buffer sizes aren't even that large IMHO.

So maybe his mention that the LSM storage was underwhelming was overblown :-) I don't know.

Another difference is with other LSM-based systems that aren't just key-value, it's usually in the context of column stores: you keep a separate LSM for each column family (could be 1-n columns). But I can't think off the top of my head how this would cause a difference. Perhaps in how reads happen - the query engines work quite differently.

Anyway, my talk is cheap, I'm just guessing here, actually doing the analysis is the hard work :-) Also, I'm something of an amateur currently, so take my words with a grain of salt. Anyone else have any ideas re: this?

SQLite is one of my favorite pieces of software for this exact reason, that it is actually a more or less "finished" program instead of a mire of shifting design requirements and constant security updates, a comfortably static and unchanging object against the chaotic backdrop of modern software development.

I read somewhere the other day that sqlite is used somewhere in Airbus A380 passenger jets, and Airbus have a support contract for it.