rc_t btree_impl::_sx_split_if_needed (btree_page_h &page, const w_keystr_t &new_key) {
bool need_split =
!page.check_space_for_insert_node(new_key)
|| (page.is_insertion_extremely_skewed_right()
&& page.check_chance_for_norecord_split(new_key));
if (!need_split) {
return RCOK; // easy
}
PageID new_page_id;
// we are running user transaction. simply call SSX split.
W_DO(_sx_split_foster(page, new_page_id, new_key));
// After split, the new page might be the parent of the new_key now.
if (!page.fence_contains(new_key)) {
btree_page_h new_page;
W_DO(new_page.fix_nonroot(page, new_page_id, LATCH_EX));
w_assert1(new_page.fence_contains(new_key));
page.unfix();
page = new_page;
}
return RCOK;
}
rc_t bt_cursor_t::_advance_one_slot(btree_page_h &p, bool &eof)
{
w_assert1(p.is_fixed());
w_assert1(_slot <= p.nrecs());
if(_forward) {
++_slot;
} else {
--_slot;
}
eof = false;
// keep following the next page.
// because we might see empty pages to skip consecutively!
while (true) {
bool time2move = _forward ? (_slot >= p.nrecs()) : _slot < 0;
if (time2move) {
// Move to right(left) sibling
bool reached_end = _forward ? p.is_fence_high_supremum() : p.is_fence_low_infimum();
if (reached_end) {
eof = true;
return RCOK;
}
// now, use fence keys to tell where the neighboring page exists
w_keystr_t neighboring_fence;
btree_impl::traverse_mode_t traverse_mode;
bool only_low_fence_exact_match = false;
if (_forward) {
p.copy_fence_high_key(neighboring_fence);
traverse_mode = btree_impl::t_fence_low_match;
int d = _upper.compare(neighboring_fence);
if (d < 0 || (d == 0 && !_upper_inclusive)) {
eof = true;
return RCOK;
}
if (d == 0 && _upper_inclusive) {
// we will check the next page, but the only
// possible matching is an entry with
// the low-fence..
only_low_fence_exact_match = true;
}
} else {
// if we are going backwards, the current page had
// low = [current-fence-low], high = [current-fence-high]
// and the previous page should have
// low = [?], high = [current-fence-low].
p.copy_fence_low_key(neighboring_fence);
// let's find a page which has this value as high-fence
traverse_mode = btree_impl::t_fence_high_match;
int d = _lower.compare(neighboring_fence);
if (d >= 0) {
eof = true;
return RCOK;
}
}
p.unfix();
// take lock for the fence key
if (_needs_lock) {
lockid_t lid (_store, (const unsigned char*) neighboring_fence.buffer_as_keystr(), neighboring_fence.get_length_as_keystr());
okvl_mode lock_mode;
if (only_low_fence_exact_match) {
lock_mode = _ex_lock ? ALL_X_GAP_N: ALL_S_GAP_N;
} else {
lock_mode = _ex_lock ? ALL_X_GAP_X : ALL_S_GAP_S;
}
// we can unconditionally request lock because we already released latch
W_DO(ss_m::lm->lock(lid.hash(), lock_mode, true, true, true));
}
// TODO this part should check if we find an exact match of fence keys.
// because we unlatch above, it's possible to not find exact match.
// in that case, we should change the traverse_mode to fence_contains and continue
W_DO(btree_impl::_ux_traverse(_store, neighboring_fence, traverse_mode, LATCH_SH, p));
_slot = _forward ? 0 : p.nrecs() - 1;
_set_current_page(p);
continue;
}
// take lock on the next key.
// NOTE: until we get locks, we aren't sure the key really becomes
// the next key. So, we use the temporary variable _tmp_next_key_buf.
const okvl_mode *mode = NULL;
{
p.get_key(_slot, _tmp_next_key_buf);
if (_forward) {
int d = _tmp_next_key_buf.compare(_upper);
if (d < 0) {
mode = _ex_lock ? &ALL_X_GAP_X : &ALL_S_GAP_S;
} else if (d == 0 && _upper_inclusive) {
mode = _ex_lock ? &ALL_X_GAP_N : &ALL_S_GAP_N;
} else {
eof = true;
mode = &ALL_N_GAP_N;
}
} else {
int d = _tmp_next_key_buf.compare(_lower);
if (d > 0) {
mode = _ex_lock ? &ALL_X_GAP_X : &ALL_S_GAP_S;
} else if (d == 0 && _lower_inclusive) {
mode = _ex_lock ? &ALL_X_GAP_X : &ALL_S_GAP_S;
} else {
eof = true;
mode = _ex_lock ? &ALL_N_GAP_X : &ALL_N_GAP_S;
}
}
}
if (_needs_lock && !mode->is_empty()) {
rc_t rc = btree_impl::_ux_lock_key (_store, p, _tmp_next_key_buf,
LATCH_SH, *mode, false);
if (rc.is_error()) {
if (rc.err_num() == eLOCKRETRY) {
W_DO(_check_page_update(p));
continue;
} else {
return rc;
}
}
}
// okay, now we are sure the _tmp_next_key_buf is the key we want to use
_key = _tmp_next_key_buf;
return RCOK; // found a record! (or eof)
}
return RCOK;
}
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;
}
}
