I found below option is more appropriate i generate numbers from concurrent session on the same time. I didnt found any duplicate number. Without below command i generate numbers and found 5 duplicate numbers. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?
Collectives on Stack Overflow. Learn more. Asked 6 years, 1 month ago. Active 6 years, 1 month ago. Viewed 12k times. Mihai Irfan Ahmad Irfan Ahmad 99 1 1 gold badge 2 2 silver badges 8 8 bronze badges. What is your storage engine? Add a comment. Active Oldest Votes. Predicate Locks for Spatial Indexes. InnoDB implements standard row-level locking where there are two types of locks, shared S locks and exclusive X locks.
A shared S lock permits the transaction that holds the lock to read a row. An exclusive X lock permits the transaction that holds the lock to update or delete a row.
If transaction T1 holds a shared S lock on row r , then requests from some distinct transaction T2 for a lock on row r are handled as follows:. A request by T2 for an S lock can be granted immediately.
As a result, both T1 and T2 hold an S lock on r. A request by T2 for an X lock cannot be granted immediately. If a transaction T1 holds an exclusive X lock on row r , a request from some distinct transaction T2 for a lock of either type on r cannot be granted immediately. Instead, transaction T2 has to wait for transaction T1 to release its lock on row r. InnoDB supports multiple granularity locking which permits coexistence of row locks and table locks. To make locking at multiple granularity levels practical, InnoDB uses intention locks.
Intention locks are table-level locks that indicate which type of lock shared or exclusive a transaction requires later for a row in a table. There are two types of intention locks:.
An intention shared lock IS indicates that a transaction intends to set a shared lock on individual rows in a table. An intention exclusive lock IX indicates that a transaction intends to set an exclusive lock on individual rows in a table. Before a transaction can acquire a shared lock on a row in a table, it must first acquire an IS lock or stronger on the table.
Before a transaction can acquire an exclusive lock on a row in a table, it must first acquire an IX lock on the table. A lock is granted to a requesting transaction if it is compatible with existing locks, but not if it conflicts with existing locks. A transaction waits until the conflicting existing lock is released. If a lock request conflicts with an existing lock and cannot be granted because it would cause deadlock , an error occurs.
The main purpose of intention locks is to show that someone is locking a row, or going to lock a row in the table. A record lock is a lock on an index record. Record locks always lock index records, even if a table is defined with no indexes.
For such cases, InnoDB creates a hidden clustered index and uses this index for record locking. See Section A gap lock is a lock on a gap between index records, or a lock on the gap before the first or after the last index record.
Gap locks are part of the tradeoff between performance and concurrency, and are used in some transaction isolation levels and not others. Gap locking is not needed for statements that lock rows using a unique index to search for a unique row. This does not include the case that the search condition includes only some columns of a multiple-column unique index; in that case, gap locking does occur. For example, if the id column has a unique index, the following statement uses only an index-record lock for the row having id value and it does not matter whether other sessions insert rows in the preceding gap:.
If id is not indexed or has a nonunique index, the statement does lock the preceding gap. It is also worth noting here that conflicting locks can be held on a gap by different transactions. For example, transaction A can hold a shared gap lock gap S-lock on a gap while transaction B holds an exclusive gap lock gap X-lock on the same gap. The reason conflicting gap locks are allowed is that if a record is purged from an index, the gap locks held on the record by different transactions must be merged.
Gap locks can co-exist. A gap lock taken by one transaction does not prevent another transaction from taking a gap lock on the same gap.
File-Per-Table Tablespaces. Temporary Tablespaces. Disabling Tablespace Path Validation. Optimizing Tablespace Space Allocation on Linux. InnoDB Transaction Model. Transaction Isolation Levels. Consistent Nonlocking Reads. How to Minimize and Handle Deadlocks. Transaction Scheduling.
InnoDB Startup Configuration. Configuring Multiple Buffer Pool Instances. Making the Buffer Pool Scan Resistant. Configuring Buffer Pool Flushing. Saving and Restoring the Buffer Pool State. Configuring Spin Lock Polling. Purge Configuration.
Configuring Persistent Optimizer Statistics Parameters. Configuring the Merge Threshold for Index Pages. InnoDB Table Compression. Overview of Table Compression. Creating Compressed Tables. InnoDB Page Compression. Defragmenting a Table. Online DDL Operations. Online DDL Limitations. Using the Compression Information Schema Tables.
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