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Important: This documentation is about an older version. It's relevant only to the release noted, many of the features and functions have been updated or replaced. Please view the current version.

Grafana Mimir binary index-header

To query series inside blocks from object storage, the store-gateway must obtain information about each block index. To obtain the required information, the store-gateway builds an index-header for each block and stores it on local disk.

The store-gateway uses GET byte range request to build the index-header, which contains specific sections of the block’s index. The store-gateway uses the index-header at query time.

Because downloading specific sections of the original block’s index is a computationally easy operation, the index-header is not uploaded to the object storage. If the index-header is not available on local disk, store-gateway instances (or the same instance after a rolling update completes without a persistent disk) re-build the index-header from the original block’s index.

Format (version 1)

The index-header is a subset of the block index and contains:

The following example shows the format of the index-header file that is located in each block store-gateway local directory. It is terminated by a table of contents that serves as an entry point into the index.

┌─────────────────────────────┬───────────────────────────────┐
│    magic(0xBAAAD792) <4b>   │      version(1) <1 byte>      │
├─────────────────────────────┬───────────────────────────────┤
│  index version(2) <1 byte>  │ index PostingOffsetTable <8b> │
├─────────────────────────────┴───────────────────────────────┤
│ ┌─────────────────────────────────────────────────────────┐ │
│ │      Symbol Table (exact copy from original index)      │ │
│ ├─────────────────────────────────────────────────────────┤ │
│ │      Posting Offset Table (exact copy from index)       │ │
│ ├─────────────────────────────────────────────────────────┤ │
│ │                          TOC                            │ │
│ └─────────────────────────────────────────────────────────┘ │
└─────────────────────────────────────────────────────────────┘