mirror of
https://github.com/Zygo/bees.git
synced 2025-05-17 05:15:45 +02:00
b7f9ce3f08
Quite often we want to execute task B after task A finishes executing, especially if tasks A and B attempt to acquire locks on the same objects. Implement that capability in Task directly: each Task holds a queue of Tasks which will be executed strictly after this Task has finished executing, or if the Task is destroyed. Add a local queue to each TaskConsumer. This queue contains a list of Tasks which are to be executed by a single thread in sequential order. These tasks are executed before fetching any tasks from TaskMaster. Each time a Task finishes executing, the list of tasks appended to the recently executed Task are spliced at the beginning of the thread's TaskConsumer local queue. These tasks will be executed in the same thread in the same order they were appended to the recently executed Task. If a Task is destroyed with a post-execution queue, that queue is also inserted at the front of the current TaskConsumer's local queue. If a Task is destroyed or somehow executed outside of a TaskConsumer thread, or a TaskConsumer thread is destroyed, the local queue of Tasks is wrapped in a "rescue_task" Task, and spliced before the head of the global queue. This preserves the sequential ordering of tasks. In all cases the order of sequential execution of Tasks that are appended to another Task is preserved. The unused queue insertion functions are removed. Exclusion is now simply a mutex, a bool, and a Task with an empty function. Tasks that queue up waiting for the mutex are stored in Exclusion's Task, and Exclusion simply runs that task when the ExclusionState is released. Signed-off-by: Zygo Blaxell <bees@furryterror.org>
BEES
Best-Effort Extent-Same, a btrfs deduplication agent.
About bees
bees is a block-oriented userspace deduplication agent designed for large btrfs filesystems. It is an offline dedupe combined with an incremental data scan capability to minimize time data spends on disk from write to dedupe.
Strengths
- Space-efficient hash table and matching algorithms - can use as little as 1 GB hash table per 10 TB unique data (0.1GB/TB)
- Daemon incrementally dedupes new data using btrfs tree search
- Works with btrfs compression - dedupe any combination of compressed and uncompressed files
- NEW Works around
btrfs sendproblems with dedupe and incremental parent shapshots - Works around btrfs filesystem structure to free more disk space
- Persistent hash table for rapid restart after shutdown
- Whole-filesystem dedupe - including snapshots
- Constant hash table size - no increased RAM usage if data set becomes larger
- Works on live data - no scheduled downtime required
- Automatic self-throttling based on system load
Weaknesses
- Whole-filesystem dedupe - has no include/exclude filters, does not accept file lists
- Requires root privilege (or
CAP_SYS_ADMIN) - First run may require temporary disk space for extent reorganization
- First run may increase metadata space usage if many snapshots exist
- Constant hash table size - no decreased RAM usage if data set becomes smaller
- btrfs only
Installation and Usage
Recommended Reading
- bees Gotchas
- btrfs kernel bugs - especially DATA CORRUPTION WARNING
- bees vs. other btrfs features
- What to do when something goes wrong
More Information
Bug Reports and Contributions
Email bug reports and patches to Zygo Blaxell bees@furryterror.org.
You can also use Github:
https://github.com/Zygo/bees
Copyright & License
Copyright 2015-2018 Zygo Blaxell bees@furryterror.org.
GPL (version 3 or later).