store-gateway: remove support for TSDB index format v1 #13808
Description
Today, store-gateways technically support TSDB index format v1 and TSDB index format v2 in a variety of places in the store-gateway.
v1 of the TSDB index format hasn't been the default for blocks created by Prometheus since before version 2.2 which was released in 2018. It has never been the default for blocks created by Mimir or Cortex.
The problem with v1 of the TSDB index is that the postings offset table is not sorted which means all entries must be loaded into memory. If store-gateways had to load every entry in the table instead of only 1/32 of them, it would increase their heap usage dramatically.
I propose to:
- Prevent uploads of blocks using TSDB index v1 in the compactor.
- Remove support for reading TSDB index v1 in the store-gateway.
Our backwards compatibility guarantee says that we will retain the ability to read data written by Mimir from the last 2 years. Given that Mimir and Cortex have never used this format (and Prometheus hasn't for ~7 years) we are OK to remove it.