Re: XTM & parallel search

On 03.06.2016 16:05, Amit Kapila wrote:

On Fri, Jun 3, 2016 at 1:34 AM, Konstantin Knizhnik <k.knizhnik@postgrespro.ru> wrote:

We have to add three more functions to eXtensible Transaction Manager API (XTM):

    /*
     * Calculate transaction state size. This method is invoked by EstimateTransactionStateSpace to copy transaction
     * state to parallel workers
     */
    size_t      (*GetTransactionStateSize)(void);

    /*
     * Serialize transaction state
     */
    void        (*SerializeTransactionState)(void* ctx);

    /*
     * Deserialize transaction state
     */
    void        (*DeserializeTransactionState)(void* ctx);

In above proposal, are you suggesting to change the existing API's as well, because the parameters of function pointers don't match with exiting API's. I think it is better to consider this along with the overall XTM API.

Sorry, but right now I have not replaced existed functions 
EstimateTransactionStateSpace/SerializeTransactionState/StartParallelWorkerTransaction
with XTM indirect calls. If was my original intention, but these functions access static variable CurrentTransactionState defined in xact.c.
So if  user-defined TM wants to override this functions, it will have to invoke original functions to save/restore CurrentTransactionState. 
It is not  convenient.
This is why three XTM functions above are now called by existed xact funcations to save additional state, for example: