8076c00592
The comment in GetTransactionSnapshot() said that you "should call RegisterSnapshot or PushActiveSnapshot on the returned snap if it is to be used very long". That felt too unclear to me. Make the comment more strongly worded. To enforce that rule and to catch potential bugs where a snapshot might get invalidated while it's still in use, add an assertion to HeapTupleSatisfiesMVCC() to check that the snapshot is registered or pushed to active stack. No new bugs were found by this, but it seems like good future-proofing. It's not a great place for the check; HeapTupleSatisfiesMVCC() is in fact safe to call with an unregistered snapshot, and the assertion won't catch other unsafe uses. But it goes a long way in practice. Fix a few cases that were playing fast and loose with that and just assumed that the snapshot cannot be invalidated during a scan. Those assumptions were not wrong, but they're not performance critical, so let's drop the excuses and just register the snapshot. These were false positives found by the new assertion. Discussion: https://www.postgresql.org/message-id/7c56f180-b9e1-481e-8c1d-efa63de3ecbb@iki.fi
PostgreSQL Database Management System
This directory contains the source code distribution of the PostgreSQL database management system.
PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.