durable_data

The durable_data module is made to provide durability to data structures across restarts of code.

Usage

The following modules are exposed in mod.ts. This module persists data to the filesystem so Deno should be run with deno run <script> --allow-read=<database directory> --allow-write=<database directory>

DurableMap

A DurableMap is a TypeScript Map with durability added. All normal Map operations work in memory. The set, delete and clear operations are written to a log.

import {
  DurableMap
} from "https://deno.land/x/durable_data/mod.ts";

const dm = new DurableMap('./dbdir/dataMap.db',{
    // all options have defaults
    mode: 0o660, // 0o600 (rw- --- ---), file mode to be used
    separator: "\r\n", // "\n", separator between records
    decode: (line:string) => atob(line), // (line)=>line ,line decoder
    encode: (line:string) => btoa(line), // (line)=>line ,line encoder
});
await dm.load(); // load previously stored data
dm.set("a","value of a");
await dm.compact(); // compact record log on disk
await dm.destroy(); // destroy data stored on disk, not in memory !

DurableSet

A DurableSet is a TypeScript Set with durability added. All normal Set operations work in memory. The add, delete and clear operations are written to a log.

import {
  DurableSet
} from "https://deno.land/x/durable_data/mod.ts";

const ds = new DurableSet('./dbdir/dataSet.db', {
    // all options have defaults
    mode: 0o660, // 0o600 (rw- --- ---), file mode to be used
    separator: "\r\n", // "\n", separator between records
    decode: (line:string) => atob(line), // (line)=>line ,line decoder
    encode: (line:string) => btoa(line), // (line)=>line ,line encoder
});
await ds.load(); // load previously stored data
ds.add("value of a");
await ds.compact(); // compact record log on disk
await ds.destroy(); // destroy data stored on disk, not in memory !

API

DurableMap and DurableSet have the same api apart from the native differences between Map and Set. use deno doc to view the API.

encode/decode

The encode/decode combo can be used for all kinds of transformations including encrypt/decrypt. Make sure that decode is the inverse of encode.

Log format

The default log format is Newline Delimited JSON

For DurableMap, e.g.:

{"cmd":"set","key":"a","value":{"l0":{"l01":1,"l02":2}}}
{"cmd":"set","key":"b","value":"b"}
{"cmd":"clear"}
{"cmd":"set","key":"c","value":"c"}
{"cmd":"delete","key":"c"}
{"cmd":"set","key":"d","value":"d"}

For DurableSet, e.g:

{"cmd":"add","key":"a"}
{"cmd":"add","key":"b"}
{"cmd":"clear"}
{"cmd":"add","key":"c"}
{"cmd":"delete","key":"c"}
{"cmd":"add","key":"d"}

Compaction using compact() will reduce the volume by processing all updates and writing new set or add records.

Notes

• JSON.stringify and JSON.parse are used in writing and reading data, so you can only persist data that can be handled by JSON.stringify! If you wish to alter this behaviour you can either prepare your data before set or add or overload JSON.stringify and JSON.parse.

• Each database should be connected to a single process. Multiple concurrent readers/writers is not supported !