Interface BTreeLockingPolicy
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- All Known Implementing Classes:
B2INoLocking
,B2IRowLocking1
,B2IRowLocking2
,B2IRowLocking3
,B2IRowLockingRR
,B2ITableLocking3
public interface BTreeLockingPolicy
The generic.BTree directory wants to know as little about locking as possible, in order to make the code usuable by multiple implementations. But the generic code will make calls to abstract lock calls implemented by concrete btree implementations. Concrete implementations like B2I understand locking, and needs informatation specific to the implementation to make the lock calls.This class is created and owned by the concrete application, but is passed into and returned from the generic code when lock calls are made. Concrete implementations which do not need lock calls can just pass a null pointer where a BTreeLockingPolicy is requested.
There are 2 types of lock interfaces, lockScan*() and lockNonScan*().
The lockScan*() interfaces save the key for the current scan position before giving up the latch on the page if they have to wait for a row lock. The callers can reposition the scan using the saved key by calling
BTreeScan.reposition()
if such a situation occurs. Then the latches are reobtained, possibly on a different page if the current key has been moved to another page in the meantime. Upon return from these interfaces the row lock requested is guaranteed to have been obtained on the correct key for the row requested. These interfaces handle the special case of unique indexes where the RowLocation can change while waiting on the lock (see implementation for details), basically the lock is retryed after waiting if the RowLocation has changed.The lockNonScan*() interfaces do not save the current scan position. If these routines return that the latch was released while waiting to obtain the lock, then the caller must requeue the lock request after taking appropriate action. This action usually involves researching the tree to make sure that the correct key is locked with latches held. These interfaces do not handle the special case of unique indexes where the RowLocation can change while waiting on the lock, as the row may disappear when the latch is released to wait on the lock - thus it is necessary that the caller retry the lock if the interface returns that the latch was released.
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description boolean
lockNonScanPreviousRow(LeafControlRow current_leaf, int current_slot, FetchDescriptor lock_fetch_desc, DataValueDescriptor[] lock_template, RowLocation lock_row_loc, OpenBTree open_btree, int lock_operation, int lock_duration)
Lock the previous key.boolean
lockNonScanRow(BTree btree, LeafControlRow current_leaf, LeafControlRow aux_leaf, DataValueDescriptor[] current_row, int lock_operation)
Lock a btree row (row in memory).boolean
lockNonScanRowOnPage(LeafControlRow leaf, int slot, FetchDescriptor lock_fetch_desc, DataValueDescriptor[] lock_template, RowLocation lock_row_loc, int lock_operation)
Lock the row at the given slot.boolean
lockScanCommittedDeletedRow(OpenBTree open_btree, LeafControlRow leaf, DataValueDescriptor[] template, FetchDescriptor lock_fetch_desc, int slot_no)
Lock a btree row to determine if it is a committed deleted row.boolean
lockScanRow(OpenBTree open_btree, BTreeRowPosition pos, FetchDescriptor lock_fetch_desc, DataValueDescriptor[] lock_template, RowLocation lock_row_loc, boolean previous_key_lock, boolean forUpdate, int lock_operation)
Lock a row as part of doing the scan.void
unlockScanRecordAfterRead(BTreeRowPosition pos, boolean forUpdate)
Release read lock on a row.
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Method Detail
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lockScanCommittedDeletedRow
boolean lockScanCommittedDeletedRow(OpenBTree open_btree, LeafControlRow leaf, DataValueDescriptor[] template, FetchDescriptor lock_fetch_desc, int slot_no) throws StandardException
Lock a btree row to determine if it is a committed deleted row.Request an exclusive lock on the row located at the given slot, NOWAIT. Return true if the lock is granted, otherwise false.
- Parameters:
open_btree
- The conglomerate we are locking.leaf
- The leaf page with the row to lock.template
- Empty full template row, to read row into.slot_no
- The slot of row on "current_leaf"- Throws:
StandardException
- Standard exception policy.
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lockScanRow
boolean lockScanRow(OpenBTree open_btree, BTreeRowPosition pos, FetchDescriptor lock_fetch_desc, DataValueDescriptor[] lock_template, RowLocation lock_row_loc, boolean previous_key_lock, boolean forUpdate, int lock_operation) throws StandardException
Lock a row as part of doing the scan.Lock the row at the given slot (or the previous row if slot is 0).
If this routine returns true all locks were acquired while maintaining the latch on leaf. If this routine returns false, locks may or may not have been acquired, and the routine should be called again after the client has researched the tree to reget the latch on the appropriate page.
- Parameters:
open_btree
- The open_btree to associate latches with - used if routine has to scan backward.pos
- Description of position of row to lock.lock_template
- A scratch area to use to read in rows.previous_key_lock
- Is this a previous key lock call?forUpdate
- Is the scan for update or for read only.lock_operation
- For what operation are we requesting the lock, this should be one of the following 4 options: LOCK_READ [read lock], (LOCK_INS | LOCK_UPD) [ lock for insert], (LOCK_INSERT_PREVKEY | LOCK_UPD) [lock for previous key to insert], (LOCK_UPD) [lock for delete or replace]- Returns:
- Whether locks were acquired without releasing latch on leaf.
- Throws:
StandardException
- Standard exception policy.
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unlockScanRecordAfterRead
void unlockScanRecordAfterRead(BTreeRowPosition pos, boolean forUpdate) throws StandardException
Release read lock on a row.- Parameters:
pos
- Data structure that defines the current position in the scan to be unlocked.forUpdate
- Is the scan for update or for read only.- Throws:
StandardException
- Standard exception policy.
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lockNonScanPreviousRow
boolean lockNonScanPreviousRow(LeafControlRow current_leaf, int current_slot, FetchDescriptor lock_fetch_desc, DataValueDescriptor[] lock_template, RowLocation lock_row_loc, OpenBTree open_btree, int lock_operation, int lock_duration) throws StandardException
Lock the previous key.Given the current latched page and slot number, lock the logically previous key in the table. There are 3 cases:
slotnumber > 1 - just lock (slotnumber - 1) (slotnumber == 1) && (leftmost leaf) - this is the first key in the table, so lock a "magic" FIRSTKEY. (slotnumber == 1) && !(leftmost leaf)- traverse left in the tree looking for a previous key.
On successful return from this routine appropriate locking will have been done. All locks and latches are requested nowait, if any lock/latch cannot be granted this routine releases the current_leaf latch and any latches it may have acquired and returns "false."
All extra latches that may have been gotten will have been released.
This routine will find the "previous row" to the (current_leaf, current_slot), walking left in the tree as necessary, and first request the lock on that row NOWAIT. If that lock can not be granted, then it will release all latches that it has acquired up to that point including the latched current_leaf passed into the routine, and request the lock WAIT. Once the lock has been granted the routine will return and it is up to the caller to research the tree to find where the current position may have ended up. For instance in the case of insert once the current latch is released, the correct page to do the insert may no longer be where the original scan found it.
If routine returns true, lock was granted NOWAIT, current leaf remains latched, and was never unlatched. If routine returns false, lock was granted WAIT, current leaf is not latched, row may have moved in the btree so caller must research to find the row.
- Parameters:
current_leaf
- Latched current leaf where "current" key is.current_slot
- The slot of row on "current_leaf"lock_template
- Empty full template row, to read row into.open_btree
- The open_btree to associate latches with - used if routine has to scan backward.lock_operation
- For what operation are we requesting the lock, this should be one of the following 4 options: LOCK_READ [read lock], (LOCK_INS | LOCK_UPD) [ lock for insert], (LOCK_INSERT_PREVKEY | LOCK_UPD) [lock for previous key to insert], (LOCK_UPD) [lock for delete or replace]lock_duration
- For what duration should the lock be held, if INSTANT_DURATION, then the routine will guarantee that lock was acquired while holding the latch, but then immediately release the lock. If COMMIT_DURATION or MANUAL_DURATION then the lock be held when routine returns successfully.- Throws:
StandardException
- Standard exception policy.
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lockNonScanRow
boolean lockNonScanRow(BTree btree, LeafControlRow current_leaf, LeafControlRow aux_leaf, DataValueDescriptor[] current_row, int lock_operation) throws StandardException
Lock a btree row (row in memory). Meant to be used if caller has the entire row objectified.Lock a btree row, enforcing the standard lock/latch protocol. On return the row is locked. Return status indicates if the lock was waited for, which will mean a latch was dropped while waiting. In general a false status means that the caller will either have to research the tree unless some protocol has been implemented that insures that the row will not have moved while the latch was dropped.
This routine request a row lock NOWAIT on the in-memory row "current_row.". If the lock is granted the routine will return true. If the lock cannot be granted NOWAIT, then the routine will release the latch on "current_leaf" (if current_leaf is non-null) and "aux_leaf" (if aux_leaf is non-null), and then it will request a WAIT lock on the row.
- Parameters:
btree
- The conglomerate we are locking.current_leaf
- If non-null, this leaf is unlatched if the routine has to wait on the lock.aux_leaf
- If non-null, this leaf is unlatched if the routine has to wait on the lock.current_row
- In memory, objectified "current" row.lock_operation
- For what operation are we requesting the lock, this should be one of the following 4 options: LOCK_READ [read lock], (LOCK_INS | LOCK_UPD) [ lock for insert], (LOCK_INSERT_PREVKEY | LOCK_UPD) [lock for previous key to insert], (LOCK_UPD) [lock for delete or replace]- Throws:
StandardException
- Standard exception policy.
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lockNonScanRowOnPage
boolean lockNonScanRowOnPage(LeafControlRow leaf, int slot, FetchDescriptor lock_fetch_desc, DataValueDescriptor[] lock_template, RowLocation lock_row_loc, int lock_operation) throws StandardException
Lock the row at the given slot.If this routine returns true all locks were acquired while maintaining the latch on leaf. If this routine returns false, locks may or may not have been acquired, and the routine should be called again after the client has researched the tree to reget the latch on the appropriate page.
- Parameters:
leaf
- The control row of the current leaf to lock.slot
- The slot position of the row to lock.lock_template
- A scratch area to use to read in rows.lock_operation
- For what operation are we requesting the lock, this should be one of the following 4 options: LOCK_READ [read lock], (LOCK_INS | LOCK_UPD) [ lock for insert], (LOCK_INSERT_PREVKEY | LOCK_UPD) [lock for previous key to insert], (LOCK_UPD) [lock for delete or replace]- Returns:
- Whether locks were acquired without releasing latch on leaf.
- Throws:
StandardException
- Standard exception policy.
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