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Local deadlock definition12/6/2023 If a query has failed because it waited long enough to exceed the lock_ wait_ timeout, identify the transaction that is causing the timeout, and kill its connection. To prevent the issue from recurring, ensure that all the transactions are committed or rolled back. To resolve the issue, identify the idle transaction and kill its connection. This happens most often when the open transaction is idle and unnecessarily holding the locks. If the query has to wait for more than the lock_ wait_ timeout (default 60 seconds), it fails. Open transactions hold the locks on rows affected by the transaction until they are committed or rolled back, and any other write query modifying the same rows has to wait for the open transaction to release the locks. For example, if node 1 hits a duplicate key error, node 2 will still commit its transaction. Hence, write queries that span across multiple nodes, commit locally when the processing finishes on the node.īy turning off multi-statement transactions, write queries that touch multiple nodes will commit locally when the processing finishes on the node. SET GLOBAL multistatement_transactions = off ĭisabling multistatement_ transactions turns off cross-node transactions for write queries. Note: This solution will not resolve a deadlock (defined previously).įor example, if the following query generates a lock wait timeout exceeded error: Adding indexes to the columns ensures that the row locks are taken in the same order that the write statements are specified in each transaction. To resolve contention when two or more transactions are writing to the same row (in the same order), add indexes on the columns being updated. If the query q1 wants to write to rows r1 and then r2, but the query q2 wants to write to row r2 first and then r1, they will deadlock.Ī single transaction that runs multiple statements should not deadlock itself, because queries are executed in the order they are defined. For example, consider two concurrently running queries q1 and q2 in different transactions, where both q1 and q2 want to write to rows r1 and r2. Typically, a deadlock happens when two or more transactions are writing to the same rows, but in a different order. The Lock wait timeout exceeded try restarting transaction error will occur when a query cannot proceed because it is blocked by a rowlock. See Locking in Columnstores for more information. Updates and deletes on a columnstore table lock the entire table if the count of rows being updated is greater than columnstore_ disk_ insert_ threshold. If a row is currently locked by query q1 running in transaction t1, a second query q2 in transaction t2 that operates on the same row will be blocked until q1 completes. Updates and deletes in SingleStore are row locking operations. Refer to the following sections to resolve lock wait timeout errors. Rowlock timeout errors can occur in an application because of contention with transactions or uncommitted transactions.
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