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diff --git a/locale/eo/LC_MESSAGES/_articles/2020-11-12-durable-persistent-trees-and-parser-combinators-building-a-database.po b/locale/eo/LC_MESSAGES/_articles/2020-11-12-durable-persistent-trees-and-parser-combinators-building-a-database.po new file mode 100644 index 0000000..5cb9491 --- /dev/null +++ b/locale/eo/LC_MESSAGES/_articles/2020-11-12-durable-persistent-trees-and-parser-combinators-building-a-database.po @@ -0,0 +1,342 @@ +# +msgid "" +msgstr "" + +msgid "" +"title: Durable persistent trees and parser combinators - building a database" +msgstr "" + +msgid "date: 2020-11-12" +msgstr "" + +msgid "layout: post" +msgstr "" + +msgid "lang: en" +msgstr "" + +msgid "" +"ref: durable-persistent-trees-and-parser-combinators-building-a-database" +msgstr "" + +msgid "category: mediator" +msgstr "" + +msgid "" +"I've received with certain frequency messages from people wanting to know if" +" I've made any progress on the database project [I've written about]({% link" +" _articles/2020-08-31-the-database-i-wish-i-had.md %})." +msgstr "" + +msgid "" +"There are a few areas where I've made progress, and here's a public post on " +"it." +msgstr "" + +msgid "Proof-of-concept: DAG log" +msgstr "" + +msgid "" +"The main thing I wanted to validate with a concrete implementation was the " +"concept of modeling a DAG on a sequence of datoms." +msgstr "" + +msgid "" +"The notion of a *datom* is a rip-off from Datomic, which models data with " +"time aware *facts*, which come from RDF. RDF's fact is a triple of subject-" +"predicate-object, and Datomic's datoms add a time component to it: subject-" +"predicate-object-time, A.K.A. entity-attribute-value-transaction:" +msgstr "" + +msgid "" +"[[person :likes \"pizza\" 0 true]\n" +" [person :likes \"bread\" 1 true]\n" +" [person :likes \"pizza\" 1 false]]\n" +msgstr "" + +msgid "The above datoms say:" +msgstr "" + +msgid "at time 0, `person` like pizza;" +msgstr "" + +msgid "at time 1, `person` stopped liking pizza, and started to like bread." +msgstr "" + +msgid "" +"Datomic ensures total consistency of this ever growing log by having a " +"single writer, the transactor, that will enforce it when writing." +msgstr "" + +msgid "" +"In order to support disconnected clients, I needed a way to allow multiple " +"writers, and I chose to do it by making the log not a list, but a directed " +"acyclic graph (DAG):" +msgstr "" + +msgid "" +"[[person :likes \"pizza\" 0 true]\n" +" [0 :parent null 0 true]\n" +" [person :likes \"bread\" 1 true]\n" +" [person :likes \"pizza\" 1 false]\n" +" [1 :parent 0 1 true]]\n" +msgstr "" + +msgid "" +"The extra datoms above add more information to build the directionality to " +"the log, and instead of a single consistent log, the DAG could have multiple" +" leaves that coexist, much like how different Git branches can have " +"different \"latest\" commits." +msgstr "" + +msgid "" +"In order to validate this idea, I started with a Clojure implementation. The" +" goal was not to write the actual final code, but to make a proof-of-concept" +" that would allow me to test and stretch the idea itself." +msgstr "" + +msgid "" +"This code [already " +"exists](https://git.euandreh.xyz/mediator/tree/src/core/clojure/src/mediator.clj?id=db4a727bc24b54b50158827b34502de21dbf8948#n1)," +" but is yet fairly incomplete:" +msgstr "" + +msgid "" +"the building of the index isn't done yet (with some [commented " +"code](https://git.euandreh.xyz/mediator/tree/src/core/clojure/src/mediator.clj?id=db4a727bc24b54b50158827b34502de21dbf8948#n295)" +" on the next step to be implemented)" +msgstr "" + +msgid "" +"the indexing is extremely inefficient, with " +"[more](https://git.euandreh.xyz/mediator/tree/src/core/clojure/src/mediator.clj?id=db4a727bc24b54b50158827b34502de21dbf8948#n130)" +" " +"[than](https://git.euandreh.xyz/mediator/tree/src/core/clojure/src/mediator.clj?id=db4a727bc24b54b50158827b34502de21dbf8948#n146)" +" " +"[one](https://git.euandreh.xyz/mediator/tree/src/core/clojure/src/mediator.clj?id=db4a727bc24b54b50158827b34502de21dbf8948#n253)" +" occurrence of `O²` functions;" +msgstr "" + +msgid "no query support yet." +msgstr "" + +msgid "Top-down *and* bottom-up" +msgstr "" + +msgid "" +"However, as time passed and I started looking at what the final " +"implementation would look like, I started to consider keeping the PoC " +"around." +msgstr "" + +msgid "" +"The top-down approach (Clojure PoC) was in fact helping guide me with the " +"bottom-up, and I now have \"promoted\" the Clojure PoC into a \"reference " +"implementation\". It should now be a finished implementation that says what " +"the expected behaviour is, and the actual code should match the behaviour." +msgstr "" + +msgid "" +"The good thing about a reference implementation is that it has no " +"performance of resources boundary, so if it ends up being 1000x slower and " +"using 500× more memory, it should be find. The code can be also 10x or 100x " +"simpler, too." +msgstr "" + +msgid "Top-down: durable persistent trees" +msgstr "" + +msgid "" +"In promoting the PoC into a reference implementation, this top-down approach" +" now needs to go beyond doing everything in memory, and the index data " +"structure now needs to be disk-based." +msgstr "" + +msgid "" +"Roughly speaking, most storage engines out there are based either on B-Trees" +" or LSM Trees, or some variations of those." +msgstr "" + +msgid "" +"But when building an immutable database, update-in-place B-Trees aren't an " +"option, as it doesn't accommodate keeping historical views of the tree. LSM " +"Trees may seem a better alternative, but duplication on the files with " +"compaction are also ways to delete old data which is indeed useful for a " +"historical view." +msgstr "" + +msgid "" +"I think the thing I'm after is a mix of a Copy-on-Write B-Tree, which would " +"keep historical versions with the write IO cost amortization of memtables of" +" LSM Trees. I don't know of any B-Tree variant out there that resembles " +"this, so I'll call it \"Flushing Copy-on-Write B-Tree\"." +msgstr "" + +msgid "" +"I haven't written any code for this yet, so all I have is a high-level view " +"of what it will look like:" +msgstr "" + +msgid "" +"like Copy-on-Write B-Trees, changing a leaf involves creating a new leaf and" +" building a new path from root to the leaf. The upside is that writes a lock" +" free, and no coordination is needed between readers and writers, ever;" +msgstr "" + +msgid "" +"the downside is that a single leaf update means at least `H` new nodes that " +"will have to be flushed to disk, where `H` is the height of the tree. To " +"avoid that, the writer creates these nodes exclusively on the in-memory " +"memtable, to avoid flushing to disk on every leaf update;" +msgstr "" + +msgid "" +"a background job will consolidate the memtable data every time it hits X MB," +" and persist it to disk, amortizing the cost of the Copy-on-Write B-Tree;" +msgstr "" + +msgid "" +"readers than will have the extra job of getting the latest relevant disk-" +"resident value and merge it with the memtable data." +msgstr "" + +msgid "" +"The key difference to existing Copy-on-Write B-Trees is that the new trees " +"are only periodically written to disk, and the intermediate values are kept " +"in memory. Since no node is ever updated, the page utilization is maximum as" +" it doesn't need to keep space for future inserts and updates." +msgstr "" + +msgid "" +"And the key difference to existing LSM Trees is that no compaction is run: " +"intermediate values are still relevant as the database grows. So this leaves" +" out tombstones and value duplication done for write performance." +msgstr "" + +msgid "" +"One can delete intermediate index values to reclaim space, but no data is " +"lost on the process, only old B-Tree values. And if the database ever comes " +"back to that point (like when doing a historical query), the B-Tree will " +"have to be rebuilt from a previous value. After all, the database *is* a set" +" of datoms, and everything else is just derived data." +msgstr "" + +msgid "" +"Right now I'm still reading about other data structures that storage engines" +" use, and I'll start implementing the \"Flushing Copy-on-Write B-Tree\" as I" +" learn more[^learn-more-db] and mature it more." +msgstr "" + +msgid "" +"[^learn-more-db]: If you are interested in learning more about this too, the" +" very best two resources on this subject are Andy Pavlo's \"[Intro to " +"Database " +"Systems](https://www.youtube.com/playlist?list=PLSE8ODhjZXjbohkNBWQs_otTrBTrjyohi)\"" +" course and Alex Petrov's \"[Database " +"Internals](https://www.databass.dev/)\" book." +msgstr "" + +msgid "Bottom-up: parser combinators and FFI" +msgstr "" + +msgid "I chose Rust as it has the best WebAssembly tooling support." +msgstr "" + +msgid "" +"My goal is not to build a Rust database, but a database that happens to be " +"in Rust. In order to reach client platforms, the primary API is the FFI one." +msgstr "" + +msgid "" +"I'm not very happy with current tools for exposing Rust code via FFI to the " +"external world: they either mix C with C++, which I don't want to do, or " +"provide no access to the intermediate representation of the FFI, which would" +" be useful for generating binding for any language that speaks FFI." +msgstr "" + +msgid "" +"I like better the path that the author of " +"[cbindgen](https://github.com/eqrion/cbindgen) crate " +"[proposes](https://blog.eqrion.net/future-directions-for-cbindgen/): " +"emitting an data representation of the Rust C API (the author calls is a " +"`ffi.json` file), and than building transformers from the data " +"representation to the target language. This way you could generate a C API " +"*and* the node-ffi bindings for JavaScript automatically from the Rust code." +msgstr "" + +msgid "" +"So the first thing to be done before moving on is an FFI exporter that " +"doesn't mix C and C++, and generates said `ffi.json`, and than build a few " +"transformers that take this `ffi.json` and generate the language bindings, " +"be it C, C++, JavaScript, TypeScript, Kotlin, Swift, Dart, *etc*[^ffi-" +"langs]." +msgstr "" + +msgid "" +"[^ffi-langs]: Those are, specifically, the languages I'm more interested on." +" My goal is supporting client applications, and those languages are the most" +" relevant for doing so: C for GTK, C++ for Qt, JavaScript and TypeScript for" +" Node.js and browser, Kotlin for Android and Swing, Swift for iOS, and Dart " +"for Flutter." +msgstr "" + +msgid "" +"I think the best way to get there is by taking the existing code for " +"cbindgen, which uses the [syn](https://github.com/dtolnay/syn) crate to " +"parse the Rust code[^rust-syn], and adapt it to emit the metadata." +msgstr "" + +msgid "" +"[^rust-syn]: The fact that syn is an external crate to the Rust compiler " +"points to a big warning: procedural macros are not first class in Rust. They" +" are just like Babel plugins in JavaScript land, with the extra shortcoming " +"that there is no specification for the Rust syntax, unlike JavaScript." +msgstr "" + +msgid "" +"As flawed as this may be, it seems to be generally acceptable and adopted,\n" +"which works against building a solid ecosystem for Rust.\n" +"\n" +"The alternative that rust-ffi implements relies on internals of the Rust\n" +"compiler, which isn't actually worst, just less common and less accepted.\n" +msgstr "" + +msgid "" +"I've started a fork of cbindgen: " +"[x-bindgen](https://git.euandreh.xyz/x-bindgen/). Right now it is just a " +"copy of cbindgen verbatim, and I plan to remove all C and C++ emitting code " +"from it, and add a IR emitting code instead." +msgstr "" + +msgid "" +"When starting working on x-bindgen, I realized I didn't know what to look " +"for in a header file, as I haven't written any C code in many years. So as I" +" was writing [libedn](https://git.euandreh.xyz/libedn/), I didn't know how " +"to build a good C API to expose. So I tried porting the code to C, and right" +" now I'm working on building a *good* C API for a JSON parser using parser " +"combinators: [ParsecC](https://git.euandreh.xyz/parsecc/)." +msgstr "" + +msgid "" +"After \"finishing\" ParsecC I'll have a good notion of what a good C API is," +" and I'll have a better direction towards how to expose code from libedn to " +"other languages, and work on x-bindgen then." +msgstr "" + +msgid "" +"What both libedn and ParsecC are missing right now are proper error " +"reporting, and property-based testing for libedn." +msgstr "" + +msgid "Conclusion" +msgstr "" + +msgid "" +"I've learned a lot already, and I feel the journey I'm on is worth going " +"through." +msgstr "" + +msgid "" +"If any of those topics interest you, message me to discuss more or " +"contribute! Patches welcome!" +msgstr "" |