Use Lucene912PostingsFormat on indexes whose storage efficiency is not critical. Likely index.codec is a good heuristic. Use cases that require batter space efficiency will have it set to best_compression. So if it is set to default is a good heuristic to use the stack Lucene912PostingsFormat.

This will ensure search use cases will benefit from the query time performance improvements that have been made overtime in Lucene's default postings format. For uses cases that rely on better storage efficiency we should keep using the ES812PostingsFormat and in a follow up develop new posting format that uses PFOR and take advantage of query time benefits (like #115021 describes). The latter a higher hanging fruit, then just using the stock Lucene912PostingsFormat that comes with Lucene 10.