is the deep store intended purely for backup/recovery? specifically i'm wondering: • is there any concept of cold storage where data is only persisted in the deep store and read as needed for queries? • the docs say the deep store doesn't typically (?) store indexes, and that zk stores segment metadata. are indexes stored in zk? or they're stored locally and rebuilt on restore?

Yes in OSS Pinot, deep store is for durability. • Concept of cold storage is there in OSS, but between SSD vs HDD : https://docs.pinot.apache.org/operators/operating-pinot/tiered-storage?q=tiered+stor • ZK only stores metadata. Deep store may or may not store indexes (depending on how the segments were created before pushing to deepstore - it won’t explicitly remove an index). Servers are capable to dynamically rebuild indexes as needed.