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The planner has historically been unable to convert "x NOT IN (SELECT y ...)" sublinks into anti-joins. This is because standard SQL semantics for NOT IN require that if the comparison "x = y" returns NULL, the "NOT IN" expression evaluates to NULL (effectively false), causing the row to be discarded. In contrast, an anti-join preserves the row if no match is found. Due to this semantic mismatch regarding NULL handling, the conversion was previously considered unsafe. However, if we can prove that neither side of the comparison can yield NULL values, and further that the operator itself cannot return NULL for non-null inputs, the behavior of NOT IN and anti-join becomes identical. Enabling this conversion allows the planner to treat the sublink as a first-class relation rather than an opaque SubPlan filter. This unlocks global join ordering optimization and permits the selection of the most efficient join algorithm based on cost, often yielding significant performance improvements for large datasets. This patch verifies that neither side of the comparison can be NULL and that the operator is safe regarding NULL results before performing the conversion. To verify operator safety, we require that the operator be a member of a B-tree or Hash operator family. This serves as a proxy for standard boolean behavior, ensuring the operator does not return NULL on valid non-null inputs, as doing so would break index integrity. For operand non-nullability, this patch makes use of several existing mechanisms. It leverages the outer-join-aware-Var infrastructure to verify that a Var does not come from the nullable side of an outer join, and consults the NOT-NULL-attnums hash table to efficiently verify schema-level NOT NULL constraints. Additionally, it employs find_nonnullable_vars to identify Vars forced non-nullable by qual clauses, and expr_is_nonnullable to deduce non-nullability for other expression types. The logic for verifying the non-nullability of the subquery outputs was adapted from prior work by David Rowley and Tom Lane. Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: wenhui qiu <qiuwenhuifx@gmail.com> Reviewed-by: Zhang Mingli <zmlpostgres@gmail.com> Reviewed-by: Japin Li <japinli@hotmail.com> Discussion: https://postgr.es/m/CAMbWs495eF=-fSa5CwJS6B-BaEi3ARp0UNb4Lt3EkgUGZJwkAQ@mail.gmail.com |
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| isolation | ||
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PostgreSQL tests ================ This directory contains a variety of test infrastructure as well as some of the tests in PostgreSQL. Not all tests are here -- in particular, there are more in individual contrib/ modules and in src/bin. Not all these tests get run by "make check". Check src/test/Makefile to see which tests get run automatically. authentication/ Tests for authentication (but see also below) examples/ Demonstration programs for libpq that double as regression tests via "make check" isolation/ Tests for concurrent behavior at the SQL level kerberos/ Tests for Kerberos/GSSAPI authentication and encryption ldap/ Tests for LDAP-based authentication locale/ Sanity checks for locale data, encodings, etc mb/ Tests for multibyte encoding (UTF-8) support modules/ Extensions used only or mainly for test purposes, generally not suitable for installing in production databases perl/ Infrastructure for Perl-based TAP tests recovery/ Test suite for recovery and replication regress/ PostgreSQL's main regression test suite, pg_regress ssl/ Tests to exercise and verify SSL certificate handling subscription/ Tests for logical replication