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Add cache eviction low and high watermarks (#8958)

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To allow better control the cache eviction process.

Introduce MINIO_CACHE_WATERMARK_LOW and 
MINIO_CACHE_WATERMARK_HIGH env. variables to specify 
when to stop/start cache eviction process. 

Deprecate MINIO_CACHE_EXPIRY environment variable. Cache 
gc sweeps at 30 minute intervals whenever high watermark is
reached to clear least recently accessed entries in the cache
until sufficient space is cleared to reach the low watermark.

Garbage collection uses an adaptive file scoring approach based
on last access time, with greater weights assigned to larger
objects and those with more hits to find the candidates for eviction.

Thanks to @klauspost for this file scoring algorithm

Co-authored-by: Klaus Post <klauspost@minio.io>
This commit is contained in:
poornas
2020-02-23 05:33:39 -08:00
committed by GitHub
parent 51a9d1bdb7
commit 224b4f13b8
18 changed files with 585 additions and 175 deletions
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16
docs/disk-caching/DESIGN.md
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@@ -11,30 +11,32 @@ minio gateway <name> -h
CACHE:
MINIO_CACHE_DRIVES: List of mounted cache drives or directories delimited by ","
MINIO_CACHE_EXCLUDE: List of cache exclusion patterns delimited by ","
MINIO_CACHE_EXPIRY: Cache expiry duration in days
MINIO_CACHE_QUOTA: Maximum permitted usage of the cache in percentage (0-100).
MINIO_CACHE_AFTER: Minimum number of access before caching an object.
MINIO_CACHE_WATERMARK_LOW: % of cache quota at which cache eviction stops
MINIO_CACHE_WATERMARK_HIGH: % of cache quota at which cache eviction starts
...
...
7. Start MinIO gateway to s3 with edge caching enabled on '/mnt/drive1', '/mnt/drive2' and '/mnt/export1 ... /mnt/export24',
exclude all objects under 'mybucket', exclude all objects with '.pdf' as extension
with expiry up to 40 days. Cache only those objects accessed atleast 3 times.
exclude all objects under 'mybucket', exclude all objects with '.pdf' as extension. Cache only those objects accessed atleast 3 times. Garbage collection triggers in at high water mark (i.e. cache disk usage reaches 90% of cache quota) or at 72% and evicts oldest objects by access time until low watermark is reached ( 70% of cache quota) , i.e. 63% of disk usage.
$ export MINIO_CACHE_DRIVES="/mnt/drive1,/mnt/drive2,/mnt/export{1..24}"
$ export MINIO_CACHE_EXCLUDE="mybucket/*,*.pdf"
$ export MINIO_CACHE_EXPIRY=40
$ export MINIO_CACHE_QUOTA=80
$ export MINIO_CACHE_AFTER=3
$ export MINIO_CACHE_WATERMARK_LOW=70
$ export MINIO_CACHE_WATERMARK_HIGH=90
$ minio gateway s3
```
## Assumptions
- Disk cache size defaults to 80% of your drive capacity.
- Disk cache quota defaults to 80% of your drive capacity.
- The cache drives are required to be a filesystem mount point with [`atime`](http://kerolasa.github.io/filetimes.html) support to be enabled on the drive. Alternatively writable directories with atime support can be specified in MINIO_CACHE_DRIVES
- Expiration of each cached entry takes user provided expiry as a hint, and defaults to 90 days if not provided.
- Garbage collection sweep of the expired cache entries happens whenever cache usage is > 80% of drive capacity, GC continues until sufficient disk space is reclaimed.
- Garbage collection sweep happens whenever cache disk usage reaches high watermark with respect to the configured cache quota , GC evicts least recently accessed objects until cache low watermark is reached with respect to the configured cache quota. Garbage collection runs a cache eviction sweep at 30 minute intervals.
- An object is only cached when drive has sufficient disk space.
## Behavior