[t:4468] Transaction yiled frequency changes merged to main.

                r = func(txn, item, yield, yieldv, lsn);

                if (r!=0) return r;

                count++;

                if (count%2 == 0) yield(NULL, NULL, yieldv);

                // We occassionally yield here to prevent transactions

                // from hogging the log.  This yield will allow other

                // threads to grab the ydb lock.  However, we don't

                // want any transaction doing more than one log

                // operation to always yield the ydb lock, as it must

                // wait for the ydb lock to be released to proceed.

                if (count % 8 == 0) {

                    yield(NULL, NULL, yieldv);

                }

            }

        }

        if (next_log.b == txn->spilled_rollback_head.b) {