[tamirms]

The problem

The hot events index was written one RocksDB key per posting into every ledger's commit batch, about 6,000 keys per ledger on pubnet, and each key passed through the write-ahead log, the memtable and later compaction. Those keys were most of each commit. The next PR in this stack stops doing that and instead writes a whole slab of the index at once, hundreds of thousands of entries, which needs a way to add them to a column family without paying those three costs.

The idea

RocksDB can adopt a file you wrote yourself. Write the entries in sorted order as one SST file, RocksDB's own file format, and hand it over with IngestExternalFile: RocksDB links the file into the column family without passing a byte through the write-ahead log or the memtable. If the file's keys do not overlap any key the column family already holds, it goes straight to the bottom level and is never compacted. Readers see all of its entries at once, and they are durable when the call returns.

What the store adds

Store.LoadSorted(cf, entries) writes the file under the store's own loading/ directory with the column family's own block size, filter and compression, ingests it, and fails if the keys overlap rather than creating compaction work. It holds the store's lifecycle lock so Close waits for it, and a read-write open removes files a stopped process left behind. The per-column-family options are now kept by name so the file can be given them.

CFOptions.CacheIndexAndFilterBlocks moves each file's index and filter blocks from the heap into the block cache. Without it a column family made of many loaded files grows the heap by about 100 KB per file; with it the memory bound the next PR relies on holds.

Measured

On the stress stream of #1097, 109 loaded files all sat at the bottom level with level 0 empty. With the index and filter blocks in the cache, the table readers' heap went from 10.5 MB to 0.23 MB with lookups unchanged. The ingest call took 15 to 17 ms at p50 on macOS, which is the fsync.

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