4e83b8001a
Summary: Closes https://github.com/facebook/rocksdb/pull/2219 Differential Revision: D4986642 Pulled By: lightmark fbshipit-source-id: c9328991e742768fb5caa0e88e022afb514f0c65
51 lines
2.3 KiB
Markdown
51 lines
2.3 KiB
Markdown
---
|
|
title: Bulkloading by ingesting external SST files
|
|
layout: post
|
|
author: IslamAbdelRahman
|
|
category: blog
|
|
---
|
|
|
|
## Introduction
|
|
|
|
One of the basic operations of RocksDB is writing to RocksDB, Writes happen when user call (DB::Put, DB::Write, DB::Delete ... ), but what happens when you write to RocksDB ? .. this is a brief description of what happens.
|
|
- User insert a new key/value by calling DB::Put() (or DB::Write())
|
|
- We create a new entry for the new key/value in our in-memory structure (memtable / SkipList by default) and we assign it a new sequence number.
|
|
- When the memtable exceeds a specific size (64 MB for example), we convert this memtable to a SST file, and put this file in level 0 of our LSM-Tree
|
|
- Later, compaction will kick in and move data from level 0 to level 1, and then from level 1 to level 2 .. and so on
|
|
|
|
But what if we can skip these steps and add data to the lowest possible level directly ? This is what bulk-loading does
|
|
|
|
## Bulkloading
|
|
|
|
- Write all of our keys and values into SST file outside of the DB
|
|
- Add the SST file into the LSM directly
|
|
|
|
This is bulk-loading, and in specific use-cases it allow users to achieve faster data loading and better write-amplification.
|
|
|
|
and doing it is as simple as
|
|
```cpp
|
|
Options options;
|
|
SstFileWriter sst_file_writer(EnvOptions(), options, options.comparator);
|
|
Status s = sst_file_writer.Open(file_path);
|
|
assert(s.ok());
|
|
|
|
// Insert rows into the SST file, note that inserted keys must be
|
|
// strictly increasing (based on options.comparator)
|
|
for (...) {
|
|
s = sst_file_writer.Add(key, value);
|
|
assert(s.ok());
|
|
}
|
|
|
|
// Ingest the external SST file into the DB
|
|
s = db_->IngestExternalFile({"/home/usr/file1.sst"}, IngestExternalFileOptions());
|
|
assert(s.ok());
|
|
```
|
|
|
|
You can find more details about how to generate SST files and ingesting them into RocksDB in this [wiki page](https://github.com/facebook/rocksdb/wiki/Creating-and-Ingesting-SST-files)
|
|
|
|
## Use cases
|
|
There are multiple use cases where bulkloading could be useful, for example
|
|
- Generating SST files in offline jobs in Hadoop, then downloading and ingesting the SST files into RocksDB
|
|
- Migrating shards between machines by dumping key-range in SST File and loading the file in a different machine
|
|
- Migrating from a different storage (InnoDB to RocksDB migration in MyRocks)
|