MDEV-36486 Optimizer hints are resolved against the INSERT part of IN… #3959
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Implementing a recursive descent parser for optimizer hints.
This commit introduces:
- the infrastructure for optimizer hints;
- hints for join buffering: BNL(), NO_BNL(), BKA(), NO_BKA();
- NO_ICP() hint for disabling index condition pushdown;
- MRR(), MO_MRR() hint for multi-range reads control;
- NO_RANGE_OPTIMIZATION() for disabling range optimization;
- QB_NAME() for assigning names for query blocks.
- Using Lex_ident_sys to scan identifiers, like the SQL parser does.
This fixes handling of double-quote-delimited and backtick-delimited identifiers,
as well as handling of non-ASCII identifiers.
Unescaping and converting from the client character set to the system
character set is now done using Lex_ident_cli_st and Lex_ident_sys,
like it's done in the SQL tokenizer/parser.
Adding helper methods to_ident_cli() and to_ident_sys()
in Optimizer_hint_parser::Token.
- Fixing the hint parser to report a syntax error when an empty identifiers:
SELECT /*+ BKA(``) */ * FROM t1;
- Moving a part of the code from opt_hints_parser.h to opt_hints_parser.cc
Moving these method definitions:
- Optimizer_hint_tokenizer::find_keyword()
- Optimizer_hint_tokenizer::get_token()
to avoid huge pieces of the code in the header file.
- A Lex_ident_cli_st cleanup
Fixing a few Lex_ident_cli_st methods to return Lex_ident_cli_st &
instead of void, to use them easier in the caller code.
- Fixing the hint parser to display the correct line number
Adding a new data type Lex_comment_st
(a combination of LEX_CSTRING and a line number)
Using it in sql_yacc.yy
- Getting rid of redundant dependencies on sql_hints_parser.h
Moving void LEX::resolve_optimizer_hints() from sql_lex.h to sql_lex.cc
Adding a class Optimizer_hint_parser_output, deriving from
Optimizer_hint_parser::Hint_list. Fixing the hint parser to
return a pointer to an allocated instance of Optimizer_hint_parser_output
rather than an instance of Optimizer_hint_parser::Hint_list.
This allows to use a forward declaration of Optimizer_hint_parser_output
in sql_lex.h and thus avoid dependencies on sql_hints_parser.h.
Forbid adding optimizer hints to view definitions. In the case when optimizer hints are added to the view definition at a `CREATE (OR REPLACE) VIEW`/`ALTER VIEW` statement, a warning is generated and the hints are ignored. This commit also disables ps-protocol for test cases where `Unresolved table/index name` warnings are generated. The reason for this is such warnings are generated during both PREPARE and EXECUTE stages. Since opt_hints.test has `--enable_prepare_warnings`, running it with `--ps-protocol` causes duplication of warning messages
join_cache_level=0 disables join cache buffers, but the hint BNL() now allows to employ BNL(H) buffers for particular tables or query blocks. This commit also adds a number of test cases including OUTER JOINs to make sure hints do not break the rules of join buffers application
BNL() hint effectively increases join_cache_level up to 4 if it is set to value less than 4. This commit also makes the BKA() hint override not only `join_cache_bka` optimizer switch but `join_cache_level` as well. I.e., BKA() hint enables BKA and BKAH join buffers both flat and incremental despite `join_cache_level` and `join_cache_bka` setting.
It places a limit N (a timeout value in milliseconds) on how long a statement is permitted to execute before the server terminates it. Syntax: SELECT /*+ MAX_EXECUTION_TIME(milliseconds) */ ... Only top-level SELECT statements support the hint.
Since BNL() hint does not specify which whether hashed or non-hashed join cache should be employed, allow usage of hashed ones where possible
… max_statement_time
- add a comment that opt_hints_global->check_unresolved() is never called
- improve comments
- rename everything with "resolved_children" to "fully_resolved_children"
- Opt_hints_table::adjust_key_hints() now returns value
- less "reach-back-to-parent" logic
- rename Hint "adjustment" and "resolution" (yes, both terms were used)
to "fixing". "Resolution" is already used for parse-tree objects
1. Disable opt_hint_timeout.test for embedded server. Make sure the test does not crash even when started for embedded server. Disable view-protocol since hints are not supported inside views. 2. Hints are designed to behave like regular /* ... */ comments: `SELECT /*+ " */ 1;` -- a valid SQL query However, the mysql client program waits for the closing doublequote character. Another problem is observed when there is no space character between closing `*/` of the hint and the following `*`: `SELECT /*+ some_hints(...) */* FROM t1;` In this case the client treats `/*` as a comment section opening and waits for the closing `*/` sequence. This commit fixes all of these issues
- remove get_args_printer() from hints printing
- add append_hint_arguments(THD *thd, opt_hints_enum hint, String *str)
- add more comments
- rename st_opt_hint_info::hint_name to hint_type
- add pptimizer trace support for hints
- add dbug_print_hints()
- make print_warn() not be a template
- introduce Printable_parser_rule interface, make grammar rules that
emit warnings implement it and print_warn invokes its function)
- remove Parser::Hint::append_args() as it is not used anywhere
(it used to be necessary call print_warn(... (Parser::Hint*)NULL);
This commit implements optimizer hints allowing to affect the order of joining tables: - JOIN_FIXED_ORDER similar to existing STRAIGHT_JOIN hint; - JOIN_ORDER to apply the specified table order; - JOIN_PREFIX to hint what tables should be first in the join; - JOIN_SUFFIX to hint what tables should be last in the join.
…SERT..SELECT When processing queries like INSERT INTO t1 (..) SELECT .. FROM t1, t2 ..., there is a single query block (i.e., a single SELECT_LEX) for both INSERT and SELECT parts. During hints resolution, when hints are attached to particular TABLE_LIST's, the search is performed by table name across the whole query block. So, if a table mentioned in an optimizer hint is present in the INSERT part, the hint is attached to the that table. This is obviously wrong as optimizer hints are supposed to only affect the SELECT part of and INSERT..SELECT clause. This commit disables possible attaching hints to tables in the INSERT part and fixes some other bugs related to INSERT..SELECT statements processing
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I force-pushed an improved version of the patch as the last one broke some tests |
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Input: Make the comment use Let's emit a warning if we swallow a hint. |
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…SERT..SELECT
Description
When processing queries like
INSERT INTO t1 (..) SELECT .. FROM t1, t2 ...there is a single query block (i.e., a single SELECT_LEX) for both INSERT and SELECT parts. During hints resolution, when hints are attached to particular TABLE_LIST's, the search is performed by table name across the whole query block.
So, if a table mentioned in an optimizer hint is present in the INSERT part, the hint is attached to the that tablet. This is obviously wrong as optimizer hints are supposed to only affect the SELECT part of and INSERT..SELECT clause.
This commit disables possible attaching hints to tables in the INSERT part and also disables hints resolution during mysql_prepare_insert_check_table(), which could lead to double resolution and warnings duplication
How can this PR be tested?
Test cases are added to opt_hints.test
If the changes are not amenable to automated testing, please explain why not and carefully describe how to test manually.
Basing the PR against the correct MariaDB version
mainbranch.PR quality check