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# BTree # BTree
This package contains a small library for creating and reading a static b-tree. This package contains a small library for creating and reading a static b-tree in as implicit pointer-less datastructure.
Both binary indices (i.e. sets) are supported, as well as arbitrary multiple-of-keysize key-value mappings where the data is
interlaced with the keys in the leaf nodes. This is a fairly low-level datastructure.
The b-trees are specified through a [BTreeContext](src/main/java/nu/marginalia/btree/model/BTreeContext.java) The b-trees are specified through a [BTreeContext](src/main/java/nu/marginalia/btree/model/BTreeContext.java)
which contains information about the data and index layout. which contains information about the data and index layout.
@ -13,7 +15,7 @@ read with a [BTreeReader](src/main/java/nu/marginalia/btree/BTreeReader.java).
```java ```java
BTreeContext ctx = new BTreeContext( BTreeContext ctx = new BTreeContext(
4, // num layers max 4, // num layers max
1, // entry size 1, // entry size, 1 = the leaf node has just just the key
BTreeBlockSize.BS_4096); // page size BTreeBlockSize.BS_4096); // page size
// Allocate a memory area to work in, see the array library for how to do this with files // Allocate a memory area to work in, see the array library for how to do this with files
@ -37,4 +39,8 @@ long btreeSize = writer.write(offsetInFile, items.length, slice -> {
BTreeReader reader = new BTreeReader(array, ctx, offsetInFile); BTreeReader reader = new BTreeReader(array, ctx, offsetInFile);
reader.findEntry(items[0]); reader.findEntry(items[0]);
``` ```
## Useful Resources
Youtube: [Abdul Bari, 10.2 B Trees and B+ Trees. How they are useful in Databases](https://www.youtube.com/watch?v=aZjYr87r1b8). This isn't exactly the design implemented in this library, but very well presented and a good refresher.