src/backup.rs: describe the garbage collection problem

This commit is contained in:
Dietmar Maurer 2019-03-30 16:26:52 +01:00
parent 10eea49d81
commit 8a4757342c

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@ -37,14 +37,16 @@
//!
//! * Create Index Files:
//!
//! Acquire shared lock for ChunkStore.
//! Acquire shared lock for ChunkStore (process wide).
//!
//! Note: We create temporary (.tmp) file, then do an atomic rename ...
//!
//!
//! * Garbage Collect:
//!
//! Acquire exclusive lock for ChunkStore.
//! Acquire exclusive lock for ChunkStore (process wide). If we have
//! already an shared lock for ChunkStore, try to updraged that
//! lock.
//!
//!
//! * Server Restart
@ -53,6 +55,24 @@
//! ChunkStore lock asap. Start new service with existing listening
//! socket.
//!
//!
//! # Garbage Collection
//!
//! Deleting backups is as easy as deleting the corresponding .idx
//! files. Unfortunately, this does not free up any storage, because
//! those files just contains references to chunks.
//!
//! To free up some storage, we run a garbage collection process at
//! regular intervals. The collector uses an mark and sweep
//! approach. In the first run, it scans all .idx files to mark used
//! chunks. The second run then removes all unmarked chunks from the
//! store.
//!
//! The above locking mechanism makes sure that we are the only
//! process running GC.
//!
//!
mod chunk_stat;
pub use chunk_stat::*;