MariaDB/server
Jul 2024 – Dec 2025
15 Months active
Languages Used
C++SQLCCMake
Technical Skills
C++ programmingSQL query performancedatabase optimizationC++ developmentparser developmentCode Refactoring
Sergei Petrunia
PROFILE
Sergei Petrunia
Sergey contributed to the MariaDB/server repository by developing and refining core query optimization features, focusing on performance, stability, and maintainability. He enhanced the SQL query planner to improve handling of complex OR clauses, virtual columns, and derived tables, using C++ and SQL to implement cost estimation and optimizer trace improvements. Sergey addressed critical bugs, such as crashes in derived-table joins and incorrect disk-read cost modeling, while also modernizing code through refactoring and documentation. His work demonstrated deep understanding of database internals, memory management, and test-driven development, resulting in more reliable query execution and predictable performance across diverse workloads.
Overall Statistics
Feature vs Bugs
47%Features
Repository Contributions
38Total
Bugs
16
Commits
38
Features
14
Lines of code
5,858
Activity Months15
Your Network
189 people
Work History
December 2025
3 Commits • 1 Features
Dec 1, 2025December 2025 — MariaDB/server: Key optimizer improvements delivering measurable value in query performance and reliability. Major contributions include enabling selectivity sampling and range analysis for tables without indexed conditions, and enhancing Loose Index Scan to leverage clustered primary keys when all query fields are part of the PK. These changes improve query plan quality, reduce unnecessary scans, and accelerate a subset of workloads. Work linked to MDEV-38240 and MDEV-38426 with commits 4da80ba8413ec866e614a3e612e649fc13736825, 2ce3f0d76cb6ae0dc6df1f257f28a4b7b1a00244, and 224efb91b4fc6c0df59abe6516a4931e08096d16. Overall impact: optimizer accuracy gain and potential performance improvements across representative workloads. Demonstrates strong proficiency in optimizer internals, performance debugging, and incremental, traceable code changes.
3 Commits • 1 Features
Dec 1, 2025December 2025 — MariaDB/server: Key optimizer improvements delivering measurable value in query performance and reliability. Major contributions include enabling selectivity sampling and range analysis for tables without indexed conditions, and enhancing Loose Index Scan to leverage clustered primary keys when all query fields are part of the PK. These changes improve query plan quality, reduce unnecessary scans, and accelerate a subset of workloads. Work linked to MDEV-38240 and MDEV-38426 with commits 4da80ba8413ec866e614a3e612e649fc13736825, 2ce3f0d76cb6ae0dc6df1f257f28a4b7b1a00244, and 224efb91b4fc6c0df59abe6516a4931e08096d16. Overall impact: optimizer accuracy gain and potential performance improvements across representative workloads. Demonstrates strong proficiency in optimizer internals, performance debugging, and incremental, traceable code changes.
December 2025
November 2025
3 Commits • 1 Features
Nov 1, 2025November 2025: Delivered two core engine improvements in MariaDB/server: fixed a critical segmentation fault in Group By WITH ROLLUP due to virtual column substitution, and improved the query planner's storage length estimation for keys and indexes to boost planning accuracy for large VARCHAR data types and InnoDB. These changes enhance stability, reliability, and efficiency of analytical queries, reducing crashes and enabling more predictable performance.
November 2025
3 Commits • 1 Features
Nov 1, 2025November 2025: Delivered two core engine improvements in MariaDB/server: fixed a critical segmentation fault in Group By WITH ROLLUP due to virtual column substitution, and improved the query planner's storage length estimation for keys and indexes to boost planning accuracy for large VARCHAR data types and InnoDB. These changes enhance stability, reliability, and efficiency of analytical queries, reducing crashes and enabling more predictable performance.
October 2025
2 Commits • 1 Features
Oct 1, 2025Month 2025-10 – Focused on stabilizing and clarifying the @@new_mode option in the MariaDB/server repo, delivering a permanent enablement behavior and improving user-visible help text. This work reduced configuration ambiguity and aligned with the product roadmap for safer feature flag handling.
2 Commits • 1 Features
Oct 1, 2025Month 2025-10 – Focused on stabilizing and clarifying the @@new_mode option in the MariaDB/server repo, delivering a permanent enablement behavior and improving user-visible help text. This work reduced configuration ambiguity and aligned with the product roadmap for safer feature flag handling.
October 2025
September 2025
1 Commits
Sep 1, 2025September 2025 performance summary for MariaDB/server: Delivered a critical bug fix to the query optimizer's cost model for disk-based temporary tables, improving the accuracy of disk-read cost estimation and overall plan quality.
September 2025
1 Commits
Sep 1, 2025September 2025 performance summary for MariaDB/server: Delivered a critical bug fix to the query optimizer's cost model for disk-based temporary tables, improving the accuracy of disk-read cost estimation and overall plan quality.
July 2025
1 Commits
Jul 1, 2025Summary for 2025-07: In MariaDB/server, delivered a critical stability improvement by fixing a crash in derived-table handling during add_keyuses_for_splitting. This fix updates Item_direct_view_ref attributes to prevent incorrect used_tables references, eliminating crash paths during derived-table joins. The work reduces production risk for complex queries and strengthens the correctness of query planning for derived tables.
1 Commits
Jul 1, 2025Summary for 2025-07: In MariaDB/server, delivered a critical stability improvement by fixing a crash in derived-table handling during add_keyuses_for_splitting. This fix updates Item_direct_view_ref attributes to prevent incorrect used_tables references, eliminating crash paths during derived-table joins. The work reduces production risk for complex queries and strengthens the correctness of query planning for derived tables.
July 2025
June 2025
3 Commits • 1 Features
Jun 1, 2025June 2025: Delivered focused code quality improvements and bug fixes in MariaDB/server, driving correctness and test reliability in JSON handling and query planning. The work supported data integrity, stable optimizer behavior, and clearer join-cost modeling across major versions.
June 2025
3 Commits • 1 Features
Jun 1, 2025June 2025: Delivered focused code quality improvements and bug fixes in MariaDB/server, driving correctness and test reliability in JSON handling and query planning. The work supported data integrity, stable optimizer behavior, and clearer join-cost modeling across major versions.
April 2025
4 Commits • 1 Features
Apr 1, 2025Month 2025-04 – MariaDB/server contributions focused on strengthening query planning robustness, improving maintainability, and stabilizing test outcomes. This period delivered targeted fixes and a cleanups that collectively raise reliability, performance potential, and developer productivity. Key features delivered: - Robust LooseScan query planning for subqueries: corrected invalid plan generation when using LooseScan with multiple subqueries by preventing interleaving of tables from different subqueries, resulting in more robust and predictable plans. Commit b89a1e7f358522b995c1f9240692f6b1bcdf4b31 (MDEV-36169). - JOIN ... USING column marking correctness: ensured join-order independence by fixing incorrect column marking in second table; yield consistent and efficient plans regardless of join order. Commit 8c7c144f1994b3a53772fed10fd6df6bff02c3ed (MDEV-36592). - Improve mark_common_columns clarity and robustness: refactored sql_base.cc to remove an unnecessary conditional, streamline join condition creation/linking, and ensure correct identification/processing of common columns. Commit cafd22db7970ce081bafd887359aa0a77cfb769d (Code cleanup in mark_common_columns()). - RocksDB stats level test alignment and defaults: adjusted minimum allowed statistics level and updated expected default to fix failing tests, aligning configuration with corrected behavior. Commit 5033da6ed603a560b6a80341b46375ff1296a7f1. Major bugs fixed: - Fixed invalid query plan generation for LooseScan subqueries. - Corrected join USING column marking to avoid plan dependency on join order. - Stabilized RocksDB stats level tests through configuration alignment. Overall impact and accomplishments: - Increased query plan reliability and predictability, leading to more robust execution and fewer regression risks in complex subquery scenarios. - Improved consistency and performance of join plans by eliminating join-order dependent behavior. - Strengthened test stability, reducing flaky results and improving CI confidence. - Improved maintainability through targeted code cleanup and clearer column/common column handling. Technologies/skills demonstrated: - C++ development in MariaDB core (sql_base.cc) and query planning logic. - Debugging of complex query planning paths involving subqueries and join semantics. - Interaction with RocksDB integration and test configuration. - Code quality improvements (refactoring/cleanup) and test alignment.
4 Commits • 1 Features
Apr 1, 2025Month 2025-04 – MariaDB/server contributions focused on strengthening query planning robustness, improving maintainability, and stabilizing test outcomes. This period delivered targeted fixes and a cleanups that collectively raise reliability, performance potential, and developer productivity. Key features delivered: - Robust LooseScan query planning for subqueries: corrected invalid plan generation when using LooseScan with multiple subqueries by preventing interleaving of tables from different subqueries, resulting in more robust and predictable plans. Commit b89a1e7f358522b995c1f9240692f6b1bcdf4b31 (MDEV-36169). - JOIN ... USING column marking correctness: ensured join-order independence by fixing incorrect column marking in second table; yield consistent and efficient plans regardless of join order. Commit 8c7c144f1994b3a53772fed10fd6df6bff02c3ed (MDEV-36592). - Improve mark_common_columns clarity and robustness: refactored sql_base.cc to remove an unnecessary conditional, streamline join condition creation/linking, and ensure correct identification/processing of common columns. Commit cafd22db7970ce081bafd887359aa0a77cfb769d (Code cleanup in mark_common_columns()). - RocksDB stats level test alignment and defaults: adjusted minimum allowed statistics level and updated expected default to fix failing tests, aligning configuration with corrected behavior. Commit 5033da6ed603a560b6a80341b46375ff1296a7f1. Major bugs fixed: - Fixed invalid query plan generation for LooseScan subqueries. - Corrected join USING column marking to avoid plan dependency on join order. - Stabilized RocksDB stats level tests through configuration alignment. Overall impact and accomplishments: - Increased query plan reliability and predictability, leading to more robust execution and fewer regression risks in complex subquery scenarios. - Improved consistency and performance of join plans by eliminating join-order dependent behavior. - Strengthened test stability, reducing flaky results and improving CI confidence. - Improved maintainability through targeted code cleanup and clearer column/common column handling. Technologies/skills demonstrated: - C++ development in MariaDB core (sql_base.cc) and query planning logic. - Debugging of complex query planning paths involving subqueries and join semantics. - Interaction with RocksDB integration and test configuration. - Code quality improvements (refactoring/cleanup) and test alignment.
April 2025
March 2025
3 Commits • 2 Features
Mar 1, 2025March 2025 focused on storage engine reliability and code quality improvements in MariaDB/server. Key work centered on upgrading the storage engine (RocksDB) to the latest 6.29 release, correcting an optimizer assertion related to LEFT JOIN handling within semi-joins (with additional tests), and improving code organization around derived keys generation without changing functionality. These changes collectively enhance stability, performance, and maintainability, enabling more predictable query planning and faster development cycles.
March 2025
3 Commits • 2 Features
Mar 1, 2025March 2025 focused on storage engine reliability and code quality improvements in MariaDB/server. Key work centered on upgrading the storage engine (RocksDB) to the latest 6.29 release, correcting an optimizer assertion related to LEFT JOIN handling within semi-joins (with additional tests), and improving code organization around derived keys generation without changing functionality. These changes collectively enhance stability, performance, and maintainability, enabling more predictable query planning and faster development cycles.
February 2025
5 Commits • 1 Features
Feb 1, 2025February 2025 – MariaDB/server: Delivered three core lines of work delivering stability, correctness, performance alignment, and robustness for derived tables and prepared statements. Key outcomes include fewer runtime assertions in subselect paths, improved query plan quality for materialized derived tables, and reliable re-preparation with array binding across error and DDL scenarios. These changes reduce risk of crashes, enhance performance, and improve reliability for complex query workloads. Key features delivered: - MariaDB stability and correctness fixes for subselects (reverted setup_tables condition; added assertion for leaf_tables_saved; removed redundant check in Index_prefix_calc::get_avg_frequency). Commits: 14a80f092914c966e552128f1f5ae744dad86220; 91de54e098b179f033deb1ee61fc3d7d5997f588. - Optimizer cost estimation improvements for derived tables (introduce optimizer_adjust_secondary_key_costs=fix_derived_table_read_cost; better handling of temp-table engine conversions and memory limits). Commit: 43c5d1303f5c7c726db276815c459436110f342f. - Robust prepared statements re-preparation and array binding handling (fix assertion failures on 2nd PS execution and after errors/DDL; add test test_mdev_36080). Commits: 80067a69feaeb5df30abb1bfaf7d4e713ccbf027; 33e0796e7a154e02a5e53c55cefc5d6feb4f5e6d. Major bugs fixed: - Assertion failure related to subselect handling in MariaDB/server. - Assertion failures during re-preparation for parameterized prepared statements and array binding scenarios. Overall impact and accomplishments: - Increased stability and correctness for complex query workloads involving subselects and derived tables. - Improved plan quality and performance through more accurate cost estimation for materialized derived tables. - Greater reliability and test coverage for prepared statements with parameter binding and array binding, across error and DDL transitions. Technologies/skills demonstrated: - C++ code changes in core MariaDB server components (subselect handling, index cost logic, derived table cost modeling, PS re-prep path). - Cost-based optimization tuning and memory-constrained plan generation. - Test-driven improvements with dedicated tests (e.g., test_mdev_36080) and expanded edge-case validation.
5 Commits • 1 Features
Feb 1, 2025February 2025 – MariaDB/server: Delivered three core lines of work delivering stability, correctness, performance alignment, and robustness for derived tables and prepared statements. Key outcomes include fewer runtime assertions in subselect paths, improved query plan quality for materialized derived tables, and reliable re-preparation with array binding across error and DDL scenarios. These changes reduce risk of crashes, enhance performance, and improve reliability for complex query workloads. Key features delivered: - MariaDB stability and correctness fixes for subselects (reverted setup_tables condition; added assertion for leaf_tables_saved; removed redundant check in Index_prefix_calc::get_avg_frequency). Commits: 14a80f092914c966e552128f1f5ae744dad86220; 91de54e098b179f033deb1ee61fc3d7d5997f588. - Optimizer cost estimation improvements for derived tables (introduce optimizer_adjust_secondary_key_costs=fix_derived_table_read_cost; better handling of temp-table engine conversions and memory limits). Commit: 43c5d1303f5c7c726db276815c459436110f342f. - Robust prepared statements re-preparation and array binding handling (fix assertion failures on 2nd PS execution and after errors/DDL; add test test_mdev_36080). Commits: 80067a69feaeb5df30abb1bfaf7d4e713ccbf027; 33e0796e7a154e02a5e53c55cefc5d6feb4f5e6d. Major bugs fixed: - Assertion failure related to subselect handling in MariaDB/server. - Assertion failures during re-preparation for parameterized prepared statements and array binding scenarios. Overall impact and accomplishments: - Increased stability and correctness for complex query workloads involving subselects and derived tables. - Improved plan quality and performance through more accurate cost estimation for materialized derived tables. - Greater reliability and test coverage for prepared statements with parameter binding and array binding, across error and DDL transitions. Technologies/skills demonstrated: - C++ code changes in core MariaDB server components (subselect handling, index cost logic, derived table cost modeling, PS re-prep path). - Cost-based optimization tuning and memory-constrained plan generation. - Test-driven improvements with dedicated tests (e.g., test_mdev_36080) and expanded edge-case validation.
February 2025
January 2025
7 Commits • 2 Features
Jan 1, 2025January 2025 performance summary for MariaDB/server. Focus this month was delivering high-impact features, fixing critical correctness issues, and strengthening stability to improve business value. Key outcomes include improved query optimization for virtual columns and derived GROUP BY, plus several stability and correctness fixes that reduce risk and improve reliability.
January 2025
7 Commits • 2 Features
Jan 1, 2025January 2025 performance summary for MariaDB/server. Focus this month was delivering high-impact features, fixing critical correctness issues, and strengthening stability to improve business value. Key outcomes include improved query optimization for virtual columns and derived GROUP BY, plus several stability and correctness fixes that reduce risk and improve reliability.
December 2024
2 Commits • 1 Features
Dec 1, 2024December 2024 — MariaDB/server: Implemented a major optimizer hints system refactor with trace support, removed deprecated paths, and introduced new interfaces for maintainability. Added richer diagnostic commentary and tracing to improve debugging and stability. Cleaned up related printing and parser interfaces to enable easier future maintenance and faster iteration.
2 Commits • 1 Features
Dec 1, 2024December 2024 — MariaDB/server: Implemented a major optimizer hints system refactor with trace support, removed deprecated paths, and introduced new interfaces for maintainability. Added richer diagnostic commentary and tracing to improve debugging and stability. Cleaned up related printing and parser interfaces to enable easier future maintenance and faster iteration.
December 2024
November 2024
1 Commits • 1 Features
Nov 1, 2024November 2024 monthly summary focusing on key accomplishments and business value for MariaDB/server.
November 2024
1 Commits • 1 Features
Nov 1, 2024November 2024 monthly summary focusing on key accomplishments and business value for MariaDB/server.
October 2024
1 Commits
Oct 1, 2024In Oct 2024, delivered a focused bug fix in MariaDB/server by replacing a custom prev_bits call with the existing my_set_bits in sql_select.h. This reduces redundancy, lowers maintenance risk, and directly addresses MDEV-35253 related to XA path correctness, notably xa_prepare_unlock_unmodified. Commit 9bb95de1867ca2a9283ea23d3c86560ce66f3d61 implements the change.
1 Commits
Oct 1, 2024In Oct 2024, delivered a focused bug fix in MariaDB/server by replacing a custom prev_bits call with the existing my_set_bits in sql_select.h. This reduces redundancy, lowers maintenance risk, and directly addresses MDEV-35253 related to XA path correctness, notably xa_prepare_unlock_unmodified. Commit 9bb95de1867ca2a9283ea23d3c86560ce66f3d61 implements the change.
October 2024
September 2024
1 Commits • 1 Features
Sep 1, 2024September 2024: Delivered Optimizer Hint Parser Improvements in MariaDB/server, adding const specifiers to methods, enhancing documentation with comments, and refining non-modifying annotations to improve readability and future maintenance. This work, tracked under MDEV-33281 (commit e4af72bd5d2aeb16a343e4160843eb1d10203bc7), lays groundwork for potential performance benefits and easier maintenance. No major bugs fixed this month. Overall impact: improved maintainability of optimizer hints and clearer guidance for future optimization work. Technologies: C++ (MariaDB core), optimizer design, inline documentation, git version control.
September 2024
1 Commits • 1 Features
Sep 1, 2024September 2024: Delivered Optimizer Hint Parser Improvements in MariaDB/server, adding const specifiers to methods, enhancing documentation with comments, and refining non-modifying annotations to improve readability and future maintenance. This work, tracked under MDEV-33281 (commit e4af72bd5d2aeb16a343e4160843eb1d10203bc7), lays groundwork for potential performance benefits and easier maintenance. No major bugs fixed this month. Overall impact: improved maintainability of optimizer hints and clearer guidance for future optimization work. Technologies: C++ (MariaDB core), optimizer design, inline documentation, git version control.
July 2024
1 Commits • 1 Features
Jul 1, 2024July 2024 monthly summary for MariaDB/server focusing on performance optimization in the SQL query planner. This period highlights a targeted improvement to complex OR clause handling, reducing unnecessary index_merge planning and CPU usage, with positive implications for query latency and throughput.
1 Commits • 1 Features
Jul 1, 2024July 2024 monthly summary for MariaDB/server focusing on performance optimization in the SQL query planner. This period highlights a targeted improvement to complex OR clause handling, reducing unnecessary index_merge planning and CPU usage, with positive implications for query latency and throughput.
July 2024
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Quality Metrics
Correctness96.8%
Maintainability86.8%
Architecture86.0%
Performance84.8%
AI Usage20.0%
Skills & Technologies
Programming Languages
CC++CMakeSQL
Technical Skills
Assertion HandlingBug FixingBug fixingBuild SystemsC ProgrammingC programmingC++C++ DevelopmentC++ developmentC++ programmingCharacter Set ConversionCode RefactoringCompiler DesignCost EstimationDatabase Development
Repositories Contributed To
Overview of all repositories you've contributed to across your timeline