Mutating existing persistent data (was: sqlite3)

[Stefan Monnier]

>> 1. A persistent hash table can be declared as :value-mutable t.
>>   In such case it will make an internal copy of its values ...
>> 
>> 2. A very radical approach (I consider it probably the “right” way).
>>    Add a cell-mutated-hook to Emacs Lisp VM …
>
> 3. Provide a function (SYNC-DATUM DATUM STORE),
>     and rely on user/package author to call it everytime
>     some datum which is also a part of a persistent store
>     is mutated.
>     This is probably the most flexible solution, with minimal
>     overhead, by shifting more responsibility to package authors.

I don't think it includes enough information for the persistent data to
be updated correctly in the presence of concurrent updates.

You either need the application to provide some atomicity/transaction
boundary information, or you need the application to send changes as
changes rather than as the resulting state (i.e. send "increment x by 2"
rather than "x is now 23").


        Stefan