Since DSM is not available during postmaster, if we were to create a DSA segment in place, similar to what's done in StatsShmemInit(), we would also need to ensure that the initial shared memory is sized appropriately. This is because it would need to be large enough to accommodate all user-defined tranches registered during postmaster, without having to rely on new dsm segments. From my experimentation, this sizing is not as straightforward as simply calculating # of tranches * size of a tranche entry.
I still think we should create the dsa during postmaster, as we do with StatsShmemInit, but it would be better if postmaster keeps its hands off this dshash and only normal backends can use them.
Thoughts?
Since creating a DSA segment in place during Postmaster startup still requires calculating the size of the tranche names table including the user-defined tranches, why not use static shared memory to pre-allocate a fixed sized table and arrays of size NAMEDATALEN to store the names?
If a dshash table is used to store tranche names and IDs, where would the tranche name for this table be registered?
