Re:An early look at Postgres 14: Performance and monitoring ...
by glogla on Saturday May 22, 2021 @03:33PM
(#27249609)
"Is table a heap with indexes on the side or is table a tree with other indexes on the side (i.e. 'clustered index')" is a more complicated discussion.
The former makes it possible to have MVCC (and thus gives you snapshot isolation and serializability) and makes secondary indexes perform faster, at the cost of vacuum or Oracle-style redo/undo/rollback segments with associated "Snapshot too old" issues.
The latter pretty much forces use of locking even for read so queries block each other (but don't require vacuum or something), makes clustering key selective queries perform faster than secondary index ones and makes you think really hard about the clustering key.
It's not really a feature you would have, but a complicated design tradeoff.
The former makes it possible to have MVCC (and thus gives you snapshot isolation and serializability) and makes secondary indexes perform faster, at the cost of vacuum or Oracle-style redo/undo/rollback segments with associated "Snapshot too old" issues.
The latter pretty much forces use of locking even for read so queries block each other (but don't require vacuum or something), makes clustering key selective queries perform faster than secondary index ones and makes you think really hard about the clustering key.
It's not really a feature you would have, but a complicated design tradeoff.