On 03.06.2016 16:05, Amit Kapila wrote:
On Fri, Jun 3, 2016 at 1:34 AM, Konstantin Knizhnik <k.knizh...@postgrespro.ru <mailto:k.knizh...@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
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:

    TransactionState s;
Size nxids = 6; /* iso level, deferrable, top & current XID,
                                 * command counter, XID count */

    for (s = CurrentTransactionState; s != NULL; s = s->parent)
        if (TransactionIdIsValid(s->transactionId))
            nxids = add_size(nxids, 1);
        nxids = add_size(nxids, s->nChildXids);

    nxids = add_size(nxids, nParallelCurrentXids);
    nxids = mul_size(nxids, sizeof(TransactionId));
    return add_size(nxids, TM->GetTransactionStateSize());

Konstantin Knizhnik
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

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