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(doc) Update RandomWriteFunnel documentation

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Viktor Lofgren 2024-02-06 12:35:24 +01:00
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code/libraries/random-write-funnel/readme.md
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# Random Write Funnel
This micro-library with strategies for solving the problem of [write amplification](https://en.wikipedia.org/wiki/Write_amplification) when
writing large files out of order to disk. It offers a simple API to write data to a file in a
random order, while localizing the writes.
This micro-library solves the problem of [write amplification](https://en.wikipedia.org/wiki/Write_amplification) when
writing large files out of order to disk. It does this by bucketing the writes into several temporary files,
Several strategies are available from the [RandomFileAssembler](src/main/java/nu/marginalia/rwf/RandomFileAssembler.java)
interface.
* Writing to a memory mapped file (non-solution, for small files)
* Writing to a memory buffer (for systems with enough memory)
* [RandomWriteFunnel](src/main/java/nu/marginalia/rwf/RandomWriteFunnel.java) - Not bound by memory.
The data is written in a native byte order.
## RandomWriteFunnel
The RandomWriteFunnel solves the problem by bucketing the writes into several temporary files,
which are then evaluated to construct the larger file with a more predictable order of writes.
Even though it effectively writes 2.5x as much data to disk than simply attempting to
construct the file directly, it is *much* faster than thrashing an SSD with dozens of gigabytes
of small random writes.
of small random writes, which is what tends to happen if you naively mmap a file that is larger
than the system RAM, and write to it in a random order.
## Demo
```java
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## Central Classes
* [RandomFileAssembler](src/main/java/nu/marginalia/rwf/RandomFileAssembler.java)
* [RandomWriteFunnel](src/main/java/nu/marginalia/rwf/RandomWriteFunnel.java)