67.2. Transactions and Locking
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## 67.2. Transactions and Locking #

The transaction IDs of currently executing transactions are shown in `pg_locks` in columns `virtualxid` and `transactionid`. Read-only transactions will have `virtualxid`s but NULL `transactionid`s, while both columns will be set in read-write transactions.

Some lock types wait on `virtualxid`, while other types wait on `transactionid`. Row-level read and write locks are recorded directly in the locked rows and can be inspected using the pgrowlocks extension. Row-level read locks might also require the assignment of multixact IDs (`mxid`; see Section 24.1.5.1).

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67.1. Transactions and Identifiers | Home | 67.3. Subtransactions