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The bitmap heap scan skip fetch optimization skips fetching the heap block when a page is set all-visible in the visibility map and no columns from the table are needed to satisfy the query.2b73a8cd33andc3953226a0changed the control flow of bitmap heap scan to use the read stream API. The read stream API returns buffers containing blocks to the user. To make this work with the skip fetch optimization, we keep a count of the empty tuples we need to emit for all the blocks skipped and only emit the empty tuples after processing the next block fetched from the heap or at the end of the scan. It's incorrect to recheck NULL tuples, so we must set `recheck` to false before yielding control back to BitmapHeapNext(). This was done before emitting any remaining empty tuples at the end of the scan but not for empty tuples emitted during the scan. This meant that if a page fetched from the heap did require recheck and set `recheck` to true and then we emitted empty tuples for subsequent blocks, we would get wrong results. Fix this by always setting `recheck` to false before emitting empty tuples. Reported-by: Alexander Lakhin <exclusion@gmail.com> Tested-by: Andres Freund <andres@anarazel.de> Discussion: https://postgr.es/m/496f7acd-881c-4df3-9bd3-8f8534dfec26%40gmail.com
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/.