postlite VS multiversion-concurrency-control

#. SQLite WAL mode

From https://www.sqlite.org/isolation.html https://news.ycombinator.com/item?id=32247085 :

> [sqlite] WAL mode permits simultaneous readers and writers. It can do this because changes do not overwrite the original database file, but rather go into the separate write-ahead log file. That means that readers can continue to read the old, original, unaltered content from the original database file at the same time that the writer is appending to the write-ahead log

#. superfly/litefs: aFUSE-based file system for replicating SQLite https://github.com/superfly/litefs

#. sqldiff: https://www.sqlite.org/sqldiff.html https://news.ycombinator.com/item?id=31265005

#. dolthub/dolt: https://github.com/dolthub/dolt

> Dolt can be set up as a replica of your existing MySQL or MariaDB database using standard MySQL binlog replication. Every write becomes a Dolt commit. This is a great way to get the version control benefits of Dolt and keep an existing MySQL or MariaDB database.

#. pganalyze/libpg_query: https://github.com/pganalyze/libpg_query :

> C library for accessing the PostgreSQL parser outside of the server environment

#. Ibis + Substrait [ + DuckDB ]

> ibis strives to provide a consistent interface for interacting with a multitude of different analytical execution engines, most of which (but not all) speak some dialect of SQL.

> Today, Ibis accomplishes this with a lot of help from `sqlalchemy` and `sqlglot` to handle differences in dialect, or we interact directly with available Python bindings (for instance with the pandas, datafusion, and polars backends).

> [...] `Substrait` is a new cross-language serialization format for communicating (among other things) query plans. It's still in its early days, but there is already nascent support for Substrait in Apache Arrow, DuckDB, and Velox.

#. benbjohnson/postlite: https://github.com/benbjohnson/postlite

> postlite is a network proxy to allow access to remote SQLite databases over the Postgres wire protocol. This allows GUI tools to be used on remote SQLite databases which can make administration easier.

> The proxy works by translating Postgres frontend wire messages into SQLite transactions and converting results back into Postgres response wire messages. Many Postgres clients also inspect the pg_catalog to determine system information so Postlite mirrors this catalog by using an attached in-memory database with virtual tables. The proxy also performs minor rewriting on these system queries to convert them to usable SQLite syntax.

> Note: This software is in alpha. Please report bugs. Postlite doesn't alter your database unless you issue INSERT, UPDATE, DELETE commands so it's probably safe. If anything, the Postlite process may die but it shouldn't affect your database.

#. > "Hosting SQLite Databases on GitHub Pages" (2021) re: sql.js-httpvfs, DuckDB https://news.ycombinator.com/item?id=28021766

#. awesome-db-tools https://github.com/mgramin/awesome-db-tools

Ben Johnson poked around in this space last year too https://github.com/benbjohnson/postlite

Note that this already exists on top of SQLite proper - authored by Ben Johnson (Litestream, Fly.io etc.) - https://github.com/benbjohnson/postlite

Currently, you need to SSH in and use the sqlite3 CLI on the server. There has been some work in this area but it's all still rough around the edges. I wrote a server called Postlite[1] that exposes remote SQLite databases over the Postgres wire protocol but it's very alpha. :)

I'd love to see more work in this area. Ricardo Ander-Egg wrote a remote management tool called litexplore[2] that connects over SSH to the SQLite CLI behind the scenes. I haven't used it but I think there's a lot of potential with that approach.

[1]: https://github.com/benbjohnson/postlite

[2]: https://github.com/litements/litexplore

I've not use this myself, but Ben Johnson's https://github.com/benbjohnson/postlite in front of SQlite might allow you to use PostgREST? I recall him saying on a podcast that his goal was to be able to point the large ecosystem of PG tools at SQlite.

The code is in this repository https://github.com/samsquire/multiversion-concurrency-control in MultiplexingThread.java and MultiplexProgramParser.java

https://github.com/samsquire/multiversion-concurrency-contro...

And I implemented a 3 way text diff with myers algorithm based on https://blog.jcoglan.com/2017/02/12/the-myers-diff-algorithm...

https://github.com/samsquire/text-diff

I implemented an eventually consistent mesh protocol that uses timestamps to provide last write wins

I think I lean towards per-thread sharding instead of mutex based or lock free data structures except for lockfree ringbuffers.

You can get embarassingly parallel performance if you split your data by thread and aggregate periodically.

If you need a consistent view of your entire set of data, that is slow path with sharding.

In my experiments with multithreaded software I simulate a bank where many bankaccounts are randomly withdrawn from and deposited to. https://github.com/samsquire/multiversion-concurrency-contro...

I get 700 million requests per second due to the sharding of money over accounts.

If you want some sample code to implement MVCC, I implemented MVCC in multithreaded Java as a toy example

https://github.com/samsquire/multiversion-concurrency-contro...

First read TransactionC.java then read MVCC.java

I wrote an unrolled switch statement in Java to simulate eager async/await across treads.

https://github.com/samsquire/multiversion-concurrency-contro...

The goal is that a compiler should generate this for you. This code is equivalent to the following:

   task1:

https://doc.rust-lang.org/book/ch16-00-concurrency.html

I've been working on implementing Java async/await state machine with switch statements and a scheduling loop. If the user doesn't await the async task handle, then the task's returnvalue is never handled. This is similar to the Go problem with the go statement.

https://github.com/samsquire/multiversion-concurrency-contro...

If your async call returns a handle and

yield value2++

https://github.com/samsquire/multiversion-concurrency-contro...

I am still working on allowing multiple coroutines to be in flight in parallel at the same time. At the moment the tasks share the same background thread.

I asked this stackoverflow question regarding C++ coroutines, as I wanted to use coroutines with a thread pool.

https://stackoverflow.com/questions/74520133/how-can-i-pass-...

This is very interesting. Thank you for submitting this and thank you for working on this.

I am highly interested in parallelism and high concurrency. I implemented multiversion concurrency control in Java.

https://github.com/samsquire/multiversion-concurrency-contro...

I am curious how to handle replication with high concurrency. I'm not sure how you detect dangerous reads+writes to the same key (tuples/fields) across different replica machines. In other words, multiple master.

I am aware Google uses truetime and some form of timestamp ordering and detection of interfering timestamps. But I'm not sure how to replicate that.

I began working on an algorithm to synchronize database records, do a sort, then a hash for each row where hash(row) = hash(previous_row.hash + row.data)

Then do a binary search on hashes matching/not matching. This is a synchronization algorithm I'm designing that requires minimal data transfer but multiple round trips.

The binary search would check the end of the data set for hash(replica_a.row[last]) == hash(replica_b.row[last]) then split the hash list in half and check the middle item, this shall tell you which row and which columns are different.