void bt_cursor_t::_set_current_page(btree_page_h &page) {
if (_pid != 0) {
_release_current_page();
}
w_assert1(_pid == 0);
w_assert1(_pid_bfidx.idx() == 0);
_pid = page.pid();
// pin this page for subsequent refix()
_pid_bfidx.set(page.pin_for_refix());
_lsn = page.get_page_lsn();
#ifndef USE_ATOMIC_COMMIT
w_assert1(_lsn.valid()); // must have a valid LSN for _check_page_update to work
#endif
}
rc_t
btree_impl::_ux_lock_key(
const StoreID& store,
btree_page_h& leaf,
const void* keystr,
size_t keylen,
latch_mode_t latch_mode,
const okvl_mode& lock_mode,
bool check_only
)
{
// Callers:
// 1. Top level _ux_lock_key() - I/U/D and search operations, lock conflict is possible
// 2. _ux_lock_range() - lock conflict is possible
//
// Lock conflict:
// 1. Deadlock - the asking lock is held by another transaction currently, and the
// current transaction is holding other locks already, failed
// 2. Timeout - the asking lock is held by another transaction currently, but the
// current transaction does not hold other locks, okay to retry
// For restart operation using lock re-acquisition:
// 1. On_demand or mixed UNDO - when lock conflict. it triggers UNDO transaction rollback
// this is a blocking operation, meaning the other concurrent
// transactions asking for the same lock are blocked, no deadlock
// 2. Traditional UNDO - original behavior, either deadlock error or timeout and retry
lockid_t lid (store, (const unsigned char*) keystr, keylen);
// first, try conditionally. we utilize the inserted lock entry even if it fails
RawLock* entry = nullptr;
// The lock request does the following:
// If the lock() failed to acquire lock (trying to acquire lock while holding the latch) and
// if the transaction doesn't have any other locks, because 'condition' is true, lock()
// returns immediatelly with eCONDLOCKTIMEOUT which indicates it failed to
// acquire lock but no deadlock worry and the lock entry has been created already.
// In this case caller (this function) releases latch and try again using retry_lock()
// which is a blocking operation, this is because it is safe to forever retry without
// risking deadlock
// If the lock() returns eDEADLOCK, it means lock acquisition failed and
// the current transaction already held other locks, it is not safe to retry (will cause
// further deadlocks) therefore caller must abort the current transaction
rc_t lock_rc = lm->lock(lid.hash(), lock_mode, true /*check */, false /* wait */,
!check_only /* acquire */, smthread_t::xct(),timeout_t::WAIT_IMMEDIATE, &entry);
if (!lock_rc.is_error()) {
// lucky! we got it immediately. just return.
return RCOK;
} else {
// if it caused deadlock and it was chosen to be victim, give up! (not retry)
if (lock_rc.err_num() == eDEADLOCK)
{
// The user transaction will abort and rollback itself upon deadlock detection.
// Because Express does not have a deadlock monitor and policy to determine
// which transaction to rollback during a deadlock (should abort the cheaper
// transaction), the user transaction which detects deadlock will be aborted.
w_assert1(entry == nullptr);
return lock_rc;
}
// couldn't immediately get it. then we unlatch the page and wait.
w_assert1(lock_rc.err_num() == eCONDLOCKTIMEOUT);
w_assert1(entry != nullptr);
// we release the latch here. However, we increment the pin count before that
// to prevent the page from being evicted.
pin_for_refix_holder pin_holder(leaf.pin_for_refix()); // automatically releases the pin
lsn_t prelsn = leaf.get_page_lsn(); // to check if it's modified after this unlatch
leaf.unfix();
// then, we try it unconditionally (this will block)
W_DO(lm->retry_lock(&entry, !check_only /* acquire */));
// now we got the lock.. but it might be changed because we unlatched.
w_rc_t refix_rc = leaf.refix_direct(pin_holder._idx, latch_mode);
if (refix_rc.is_error() || leaf.get_page_lsn() != prelsn)
{
// release acquired lock
if (entry != nullptr) {
w_assert1(!check_only);
lm->unlock(entry);
} else {
w_assert1(check_only);
}
if (refix_rc.is_error())
{
return refix_rc;
}
else
{
w_assert1(leaf.get_page_lsn() != prelsn); // unluckily, it's the case
return RC(eLOCKRETRY); // retry!
}
}
return RCOK;
}
}
