feat: add blob-related monitoring metrics for RocksDB BlobDB #2390
Description
Feature Request
Is your feature request related to a problem? Please describe:
When using RocksDB's BlobDB (integrated BlobDB/BlobCache), there is limited visibility into blob file statistics and blob cache performance. Currently, Pegasus only exposes SST file metrics (rdb_total_sst_size_mb, rdb_total_sst_files), but lacks metrics for blob files, making it difficult to monitor and troubleshoot BlobDB-related issues such as:
- Blob file size and garbage ratio
- Blob cache hit rate and usage
- Blob data movement during compaction
Describe the feature you'd like:
Add comprehensive blob-related monitoring metrics to Pegasus server.
Blob Size Metrics:
- rdb_total_blob_size_mb - Total size of all blob files
- rdb_live_blob_size_mb - Size of live blob files
- rdb_live_blob_garbage_size_mb - Size of garbage in live blob files
- rdb_blob_garbage_ratio - Ratio of blob garbage to total blob size
- rdb_blob_cache_capacity_bytes - Blob cache capacity
- rdb_blob_cache_usage_bytes - Blob cache usage
- rdb_blob_cache_pinned_usage_bytes - Blob cache pinned usage
- rdb_compaction_input_blob_bytes - Blob bytes read during compaction
- rdb_compaction_output_blob_bytes - Blob bytes written during compaction