Thursday, October 10, 2024

Emacs Projectile Tweaks for MySQL Development

I am using Emacs with Projectile (besides other packages) for MySQL development. Here's a couple of little tweaks to save a few keystrokes here and there:

  • Visit (which in Emacs parlance means open) the MTR test file, by its MTR name instead of file path:
;; This is a not a MySQL-specific implementation of `projectile-find-test-file'.
;; That function is meant for jumping from a source file to its test file.
;; TODO(laurynas): this is not an exhaustive implementation for all locations
;; test files can reside. Add them as the need arises.
(defun my-visit-mtr-test ()
  "Input MySQL MTR test name and visit it."
  (interactive)
  (let* ((input (read-string "MySQL MTR test name: "))
         ;; TODO(laurynas): error checking
         (parts (split-string input "\\."))
         (suite-name (car parts))
         (test-in-suite (concat "t/" (cadr parts) ".test"))
         (test-root (concat (projectile-project-root) "mysql-test/"))
         (file-path (if (string= suite-name "main")
                        (concat test-root test-in-suite)
                      (concat test-root "suite/" suite-name "/"
                              test-in-suite))))
    (find-file file-path)))

(define-key projectile-command-map "M" #'my-visit-mtr-test)

The last line binds this command to M in the Projectile command map, so if your Projectile keybinding prefix is C-c p (C is Ctrl in case non-Emacs users are still reading), you can do C-c p M to invoke it.

  • Register .test and .result files as "other file types" for each other. This way projectile-find-other-file (at e.g. C-c p a) can be used for quick jumping between tests and their results:
(add-to-list 'projectile-other-file-alist '("test" "result"))
(add-to-list 'projectile-other-file-alist '("result" "test"))

If I think of more utilities, I'll try not to forget to update this post.

Friday, September 06, 2024

Running Perl-using MTR tests for fb-mysql under macOS

The headline is slightly misleading. Oracle MySQL has several Perl-using MTR tests, the whole MTR framework is Perl-based, and those tests run fine out of the box (with an occasional bug). However, fb-mysql has additional tests that call the Random Query Generator under the hood, and these tests don't work out of the box under macOS.

Here's what I had to do to get them working:

# mysql-client default version is 9.0 now, and you'll get the wrong auth plugin error
brew install perl mysql-client@8.0

# TODO: does not survive upgrades, do what the Perl Homebrew formula advises with
# local::lib

/opt/homebrew/opt/perl/bin/cpan DBI
/opt/homebrew/opt/perl/bin/cpan JSON
/opt/homebrew/opt/perl/bin/cpan Expect

# Adjust path only for compilation below. For now I don't need it globally
export PATH="/opt/homebrew/opt/mysql-client/bin:$PATH"

# Run the following command and expect it to fail with the error as in
# https://stackoverflow.com/questions/53277884/installation-of-dbdmysql-fails-with-symbol-not-found-on-osx-mojave
/opt/homebrew/opt/perl/bin/cpan DBD::mysql

# Now go to ~/.cpan/build/DBD-mysql-<latest> and do:
perl Makefile.PL \
     --libs="-L/opt/homebrew/opt/mysql-client/lib -L/opt/homebrew/lib -lmysqlclient -lz -lzstd -lssl -lcrypto -lresolv"
sudo make install

And now:

[  5%] rocksdb.rqg_runtime 'rocksdb_ddse'       w4  [ pass ]  41533

Success! Stay tuned for getting Python tests running too.

Friday, August 23, 2024

A README for my MySQL development tooling

Over the years I have written and borrowed various bits of scripts and configuration files to make MySQL development easier by configuring and automating things. Having written patch2testlist a few months ago, I figured that now I have at least one thing that should work not only on my machine. Thus I put together a README for MySQL-related stuff in my dotfiles, also included below.

My MySQL Development Tools

Tool configuration

  • clangd: I am so glad C++ finally got universal IDE tooling and clangd is very useful for MySQL development.
  • Emacs: my primary Emacs config is elsewhere, while this is a directory-local config that takes effect in the source trees. It prevents creating spurious .ispell.dict files, sets the C++ style to Google, and makes Magit (magit-todos actually) exclude 3rd party TODO comments.
  • cpplint: cpplint is still marginally useful with MySQL sources.

I symlink these into the parent directory of all the source trees.

Could be useful to you

  • patch2testlist: for a given patch, print a list of MTR tests to run to cover the test changes in the patch. Introduced in its own blog post. Unlike the scripts below, patch2testlist is standalone and works without the zsh utility functions.

Useful to me

  • mysql-work.sh: a shell initialization script that sets up environment variables and helper functions to configure, build, & test various MySQL versions on macOS and Linux. For example, $MY8037D will expand to CMake options for a debug build of MySQL 8.0.37. As for the functions, among others, mysql_build will configure and build a given tree, and rmtr will incrementally build and run MTR tests with libeatmydata. This script adds various warning disable flags so that older unpatched trees can be built with newer compilers within reason. It also absorbs bug workarounds and complications related to build environments, for example, different MySQL versions need both OpenSSL 1.1 and 3 installed, which then in turn results in build issues if both versions are present simultaneously. This script is not usable without its zsh utility functions.
  • fetchworksrc: fetch all remotes for Git repos in WORK_REPOS_TO_PULL environment variable; pull all the worktrees in WORK_TREES_TO_UPDATE one and do incremental builds. This script runs at midnight on my work machine. There are some quality of life embellishments such as skipping the the build if the machine is a laptop on battery and managing Homebrew OpenSSL version incompatibilities in builds. Again, this script is not usable without its zsh utility functions.

zsh function library

This directory. One file per function as zsh requires. Currently they fall into two sets of responsibilities: querying the source tree for version information and managing OpenSSL 3 build workarounds.

No longer maintained (patches welcome)

  • gca, the workhorse script from my time at Percona. Used when the same patch has to be developed for more than one major MySQL series (e.g. the patch is needed for 8.0, 8.4, & 9.0, using an example that is current at the time of the writing). There is a constraint that the lower series version of the patch has to be git merged to the next higher series, but the latest commits of these series are not fully merged to each other due to how Oracle pushes their source trees. So, a lower series feature branch has to be created not from the tip but from some older commit which had been fully merged. This script manages finding such commits and creating the worktrees. Luckily I only deal with single series these days.
  • reupmerge, used in that same multiple-series workflow. It handles the scenario where, i.e. a code review change needs to be applied to a lower branch commit in a feature branch. Changing that commit requires re-merging it to the higher series. For the case where the higher series commit needs not to change, this script automates saving its diff, and re-merging the lower series with that exact saved diff.
  • mysql-work.el: mostly outdated Emacs configuration bits, mostly copied from colleagues at Percona. They set up MySQL (and InnoDB) indentation styles that were used up to 5.7, and provide a bit of syntax support for MTR .test files.

Tuesday, July 09, 2024

A MySQL 9.0.0 branch with patches

Recently I made public a branch of MySQL 8.4.0 with patches. Now that newer upstream versions have been released, I have rebased the branch on 9.0.0: patched-mysql-9.0.0.

I did not add any new patches, and dropped the LLVM compilation fix patch. Thus the current patch set improves AddressSanitizer support and includes several fixes/improvements for the clone plugin to support a second transactional storage engine:

  1. Fix for Bug 115120: Provide memory debugging macro implementations for AddressSanitizer.
  2. Fix for Bug 109922: SEs do not coordinate clone rollbacks on instance startup.
  3. Fix for Bug 109920: SEs cannot add to clone data size estimates.
  4. Fix for Bug 109919: Clone plugin does not support arbitrary length O_DIRECT files.
  5. Fix for Bug 107715: Multiple SE clone not calling clone_end after mixed clone_begin failure/success.
  6. Fix for Bug 106750: Some clone tests needlessly marked as Linux-only.
  7. Fix for Bug 106737: Wrong SE called to ack clone application if >1 SE.

Thursday, July 04, 2024

Building and testing MySQL 8.0.38 / 8.4.1 / 9.0.0 on macOS

Oracle has just released MySQL 8.0.38/8.4.1/9.0.0, so let's see how the Valgrind testing of the previous set of releases is going:

[ 65%] innodb.bug33788578_rec_IV_set            w2  [ fail ]  Found warnings/errors in error log file!

It only managed two thirds of a run (a --big-test one) in a few weeks, which means that I either need a faster machine, or that Valgrind testing does not take even remotely reasonable amount of time. Despite the run being incomplete, it resulted in couple of bug reports because every single test gives an error: #115229: pwrite(buf) points to uninitialised byte(s) in os_fusionio_get_sector_size(). I also noticed that one test always times out: #114998: Test rpl_gtid.rpl_gtid_parallel times out under Valgrind. I need to rethink Valgrind testing going forward, maybe by trying dropping --big-test first.

Back to the new releases. A nice surprise is that the they build with XCode 15.3 even though the associated bug (#113123: Compilation fails with LLVM 17 and XCode 15.3) is still open. However, an LLVM 18 build fails in the bundled zlib, and this time I refrained from reporting a bug. GCC 11–14 also fail, but they are officially unsupported for macOS, so I won't be reporting that, unless I encounter issues on Linux.

Fixed and no longer reproducing bugs:

New bugs:

Little to no changes

Finally, I did not retest #113113: Build failure with Homebrew LLVM 14-17 on macOS, where I keep using the workaround of setting CMAKE_AR to Homebrew ar.

To sum up, 5 bugs fixed or no longer reproducing, 7 new, 11 with no changes, 1 not tested, and 2 new Valgrind ones. I don't like this trend and I miss the middle-8.0 releases that were fully clean under macOS.

Friday, June 14, 2024

Implementing a Table-Returning MySQL Function

Edit: links to Percona SEQUENCE_TABLE implementation added to the end

MySQL has many native functions and it's relatively straightforward to write new ones. While the official internals manual has a chapter on adding native functions, some aspects aren't immediately obvious, such as the possible return types for functions. The linked docs suggest that functions can return a double, an integer, or a string, but doesn't mention that they can also return JSON documents (i.e. JSON_ARRAY) and relational tables (i.e. JSON_TABLE). I have filed a bug for this omission, meanwhile this post will be my attempt at documenting the implementation of table-returning functions.

We will implement a table-returning function called LAST_INSERT_IDS, We will focus on the server infrastructure to support that, not on the function's purpose or the actual data it returns. Let's do the simplest possible thing: return a table with one column and one row.

Exploring the Codebase

Grepping the source tree for JSON_TABLE points to Table_function class declared in sql/table_function.h. Source code history then points to this commit, which in turn mentions Worklog #8867 (Add JSON table functions). Luckily for us it's a relatively old worklog, thus available publicly! From the worklog we can learn that any result tables will start as in-memory temporary tables which will spill to disk as needed. Good. The worklog also touches upon a lot of stuff elsewhere in the server so that the query optimizer will know how to deal with table-returning functions. We won't need to deal with that while implementing a new function, but it may provide debugging starters should anything go wrong.

Function class

To start writing code, we have to derive a new concrete class from Table_function and let the compiler tell us what methods must be implemented:

class Table_function_last_insert_ids final : public Table_function {
 public:
  bool init() override;
  bool fill_result_table() override;
  const char *func_name() const override;
  bool print(const THD *thd, String *str,
             enum_query_type query_type) const override;
  bool walk(Item_processor processor, enum_walk walk, uchar *arg) override;

 private:
  List<Create_field> *get_field_list() override;
  bool do_init_args() override;
};

But let's not implement them just yet (stub them out with assert(0) bodies to learn what gets called when), and let's look into instantiating the class object first. The regular functions get registered with MySQL in func_array variable in sql/item_create.cc, and the surrounding code knows how to create their objects. But JSON_TABLE is not there! Grepping shows that it is wired directly to the parser, probably because its arguments are non-trivial. Our function is much simpler in that regard, can we get away with putting it there instead of patching parser? It turns out that no, we cannot, because the simpler functions derive from Item_func class, which derives from Item, which is what this infrastructure expects. And our table-returning function derives from Table_function, which has no further ancestors.

Patching the parser

OK, off to the parser we go. To find a starting point, let's check what JSON_TABLE does. Grepping for Table_function_json in the parser (the worklog is not too specific in this area), we get a match for PT_table_factor_function class in sql/parse_tree_nodes.cc. Then we grep for that class in the parser grammar and we get a hint why the table-returning functions are harder to implement than other kinds of functions:

table_function:
        JSON_TABLE_SYM '(' expr ',' text_literal columns_clause ')'
        opt_table_alias
        {
          // Alias isn't optional, follow derived's behavior
          if ($8 == NULL_CSTR)
          {
            my_message(ER_TF_MUST_HAVE_ALIAS,
                       ER_THD(YYTHD, ER_TF_MUST_HAVE_ALIAS), MYF(0));
            MYSQL_YYABORT;
          }

          $$= NEW_PTN PT_table_factor_function($3, $5, $6, to_lex_string($8));
        }
      ;

We can see that the parser knows how to work with exactly one table-returning function that is named JSON_TABLE, thus we have to patch the parser. Let's keep everything under the non-terminal symbol table_function:

table_function:
          json_table_function
        | last_insert_ids_function
        ;

last_insert_ids_function:
          LAST_INSERT_IDS_SYM '(' ')'
          opt_table_alias
          {
            // Alias isn't optional, follow derived's behavior
            if ($4 == NULL_CSTR)
            {
                my_message(ER_TF_MUST_HAVE_ALIAS,
                           ER_THD(YYTHD, ER_TF_MUST_HAVE_ALIAS), MYF(0));
                MYSQL_YYABORT;
            }

            $$= NEW_PTN PT_last_insert_ids_function(to_lex_string($4));
          }
        ;

json_table_function:
        // As before

Unfortunately the opt_table_alias block must be duplicated. But, no increase in the parser shift/reduce conflicts! There is more not particularly interesting stuff to do in the lexer and the parser:

  • Add the function name to the lexer, {SYM("LAST_INSERT_IDS", LAST_INSERT_IDS_SYM)}, to sql/lex.h.
  • Declare this lexer symbol as a token for the parser. I did not make it a keyword because JSON_TABLE wasn't one neither: %token LAST_INSERT_IDS_SYM 10024.
  • Finally, declare last_insert_ids_function symbol to be of table_reference type, same as table_function was before.

Parse Tree Node class

That's enough for the lexer and the parser, next we need to implement PT_last_insert_ids_function class:

class PT_last_insert_ids_function : public PT_table_reference {
 public:
  PT_last_insert_ids_function(const LEX_STRING &table_alias)
      : m_table_alias{table_alias} {}

 private:
  const LEX_STRING m_table_alias;
};

Without a PT_last_insert_ids_function::contextualize method, which would actually create the Table_function_last_insert_ids object, the above implementation fails rather non-obviously:

mysqltest: At line 24: Query 'SELECT * FROM LAST_INSERT_IDS() as ids' failed.
ERROR 1096 (HY000): No tables used

Let's add that method by copying, pasting, and deleting the non-applicable bits of PT_table_factor_function::contextualize. The job of this method will be to create the function object and to assign a name and a table for the query optimizer for the result.

bool PT_last_insert_ids_function::contextualize(Parse_context *pc) {
  if (super::contextualize(pc)) return true;
  auto *const fn = new (pc->mem_root) Table_function_last_insert_ids{};
  if (unlikely(fn == nullptr)) return true;

  LEX_CSTRING alias;
  alias.length = strlen(fn->func_name());
  alias.str = sql_strmake(fn->func_name(), alias.length);
  if (unlikely(alias.str == nullptr)) return true;

  auto *const ti = new (pc->mem_root) Table_ident(alias, fn);
  if (ti == nullptr) return true;

  m_table_ref = pc->select->add_table_to_list(pc->thd, ti, m_table_alias.str, 0,
                                              TL_READ, MDL_SHARED_READ);
  if (m_table_ref == nullptr || pc->select->add_joined_table(m_table_ref))
    return true;

  return false;
}

Filling out the function class implementation

This implementation forces us to define the first method in Table_function_last_insert_ids, a very simple one:

const char *func_name() const override { return "last_insert_ids"; }

Let's run it!

SELECT * FROM LAST_INSERT_IDS() as ids;
...
Assertion failed: (0), function init, file table_function.h, line 440.

…which points to the stub Table_function_last_insert_ids::init(). Let's say we have no meaningful initialization at this point, so remove the assert from the stub:

Assertion failed: (false), function get_field_list, file table_function.h, line 464.

This is get_field_list method, and we have to implement it to describe the schema of the table we will be returning:

List<Create_field> *Table_function_last_insert_ids::get_field_list() {
  assert(fields.is_empty());

  auto *const field = new Create_field;
  field->init_for_tmp_table(MYSQL_TYPE_LONGLONG, MAX_BIGINT_WIDTH,
                            DECIMAL_NOT_SPECIFIED, /* is_nullable */ false,
                            /* is_unsigned */ true, 0, "insert_id");
  fields.push_back(field);

  return &fields;
}

This implementation assumes it is not a simple getter and thus is called exactly once. If the assumption will shown to be incorrect by the assert, I'll move the code to init and will reduce this one to a simple getter. Also, something will have to free the memory we are allocating for the field, that's for later.

Run again…

Assertion failed: (false), function do_init_args, file table_function.h, line 467.

For JSON_TABLE, this method is documented to "check whether given default values can be saved to fields." Let's assume that we have no meaningful actions here, remove the assert, return success, run again:

Assertion failed: (0), function fill_result_table, file table_function.h, line 442.

Finally we get to the second serious method that should provide the payload for the result table:

bool Table_function_last_insert_ids::fill_result_table() {
  assert(!fields.is_empty());
  assert(!table->materialized);
  assert(table->s->fields == 1);

  empty_table();

  auto *const field = get_field(0);
  assert(field->field_index() == 0);
  field->store(current_thd->first_successful_insert_id_in_prev_stmt);
  field->set_notnull();
  write_row();

  return false;
}

And…

SELECT * FROM LAST_INSERT_IDS() as ids;
insert_id
0

Success!

Implementing the remaining stubs

We still have two stub methods with asserts in them: print and walk. Let's try figuring out under what conditions they get called, again, by looking at JSON_TABLE implementation.

Let's start with print. It gets called by sql_lex.cc Table_ref::print. There are references to optimizer trace and something else around that. Let's see if that "something else" refers to the good old EXPLAIN:

EXPLAIN SELECT * FROM LAST_INSERT_IDS() as ids;
Assertion failed: (false), function print, file table_function.h, line 450.
7   mysqld                              0x000000010385ffb8 Table_function_last_insert_ids::walk(bool (Item::*)(unsigned char*), enum_walk, unsigned char*) + 0

Interesting! We tried to find what calls print, but we found what calls walk instead. Since our function is atomic with regard to the query optimizer and has no internal structure, there is nothing to walk, let's remove the assert:

EXPLAIN SELECT * FROM LAST_INSERT_IDS() as ids;
Assertion failed: (false), function print, file table_function.h, line 450.

Great, so the same EXPLAIN statement exercises both walk and print. Let's add a simple implementation for the latter:

bool print(const THD *, String *str, enum_query_type) const override {
  return !str->append(STRING_WITH_LEN("last_insert_ids()"));
}

And now the EXPLAIN!

EXPLAIN SELECT * FROM LAST_INSERT_IDS() as ids;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	ids	NULL	ALL	NULL	NULL	NULL	NULL	2	100.00	Table function: last_insert_ids; Using temporary
Warnings:
Note	1003	/* select#1 */ select `ids`.`insert_id` AS `insert_id` from last_insert_ids() `ids`

Memory management

One last thing is that Field object which was allocated in Table_function_last_insert_ids::get_field_list and never freed. Let's see if the standard tooling catches this error. AddressSanitizer under Linux includes LeakSanitizer, let's try it:

==31384==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 1440 byte(s) in 6 object(s) allocated from:
    #0 0xab9c0d1a99ac in operator new(unsigned long) (/home/laurynas/vilniusdb/last_insert_ids/_build-debug-llvm-14-san/runtime_output_directory/mysqld+0xb0599ac) (BuildId: 611e155cd8dc43455bd5d5e0ddbdfe53ae205fa4)
    #1 0xab9c0e6bb8bc in Table_function_last_insert_ids::get_field_list() /home/laurynas/vilniusdb/last_insert_ids/sql/table_function.cc:778:23
    #2 0xab9c0e6b5514 in Table_function::create_result_table(THD*, unsigned long long, char const*) /home/laurynas/vilniusdb/last_insert_ids/sql/table_function.cc:64:46
    #3 0xab9c0e0024fc in Table_ref::setup_table_function(THD*) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_derived.cc:933:23
    #4 0xab9c0e388bfc in Query_block::resolve_placeholder_tables(THD*, bool) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_resolver.cc:1310:15
    #5 0xab9c0e3854a4 in Query_block::prepare(THD*, mem_root_deque<Item*>*) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_resolver.cc:247:7
    #6 0xab9c0e3e3da4 in Sql_cmd_select::prepare_inner(THD*) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_select.cc:484:17
    #7 0xab9c0e3e2d74 in Sql_cmd_dml::prepare(THD*) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_select.cc:399:11
    #8 0xab9c0e3e4360 in Sql_cmd_dml::execute(THD*) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_select.cc:539:9
    #9 0xab9c0e263934 in mysql_execute_command(THD*, bool, unsigned long long*) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_parse.cc:5489:29
    #10 0xab9c0e25c8c8 in dispatch_sql_command(THD*, Parser_state*, unsigned long long*) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_parse.cc:6276:21
    #11 0xab9c0e253894 in dispatch_command(THD*, COM_DATA const*, enum_server_command) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_parse.cc:2565:7
    #12 0xab9c0e259124 in do_command(THD*) /home/laurynas/vilniusdb/last_insert_ids/sql/sql_parse.cc:1745:18
    #13 0xab9c0e7f6f10 in handle_connection(void*) /home/laurynas/vilniusdb/last_insert_ids/sql/conn_handler/connection_handler_per_thread.cc:307:13
    #14 0xab9c12076ee8 in pfs_spawn_thread(void*) /home/laurynas/vilniusdb/last_insert_ids/storage/perfschema/pfs.cc:3022:3
    #15 0xfbb124cc5978 in start_thread nptl/./nptl/pthread_create.c:447:8
    #16 0xfbb124d2ba48 in thread_start misc/../sysdeps/unix/sysv/linux/aarch64/clone3.S:76

Yep, a leak. Let's try freeing that memory in the destructor:

Table_function_last_insert_ids::~Table_function_last_insert_ids() {
  assert(fields.elements == 1);
  delete fields.head();
}

Run again, no leak or any other Sanitizer error.

Summary checklist

So, to summarize, the checklist for adding a new table-returning function to MySQL:

  • Add the function name as a lexer symbol in sql/lex.h
  • Add the function name symbol as a token in the parser (sql/sql_yacc.yy)
  • In the parser, rename table_function to json_table_function and add new table_function with json_table_function and new function alternatives. All these symbols must be typed as table_reference
  • Create a new parse tree node class, for example:
class PT_last_insert_ids_function : public PT_table_reference {
  using super = PT_table_reference;

 public:
  PT_last_insert_ids_function(const LEX_STRING &table_alias)
      : m_table_alias{table_alias} {}

  bool contextualize(Parse_context *pc) override;

 private:
  const LEX_STRING m_table_alias;
};

bool PT_last_insert_ids_function::contextualize(Parse_context *pc) {
  if (super::contextualize(pc)) return true;
  auto *const fn = new (pc->mem_root) Table_function_last_insert_ids{};
  if (unlikely(fn == nullptr)) return true;

  LEX_CSTRING alias;
  alias.length = strlen(fn->func_name());
  alias.str = sql_strmake(fn->func_name(), alias.length);
  if (unlikely(alias.str == nullptr)) return true;

  auto *const ti = new (pc->mem_root) Table_ident(alias, fn);
  if (ti == nullptr) return true;

  m_table_ref = pc->select->add_table_to_list(pc->thd, ti, m_table_alias.str, 0,
                                              TL_READ, MDL_SHARED_READ);
  if (m_table_ref == nullptr || pc->select->add_joined_table(m_table_ref))
    return true;

  return false;
}
  • Create a new table function class:
class Table_function_last_insert_ids final : public Table_function {
 public:
  ~Table_function_last_insert_ids() override;

  bool init() override { return false; }

  bool fill_result_table() override;

  const char *func_name() const override { return "last_insert_ids"; }

  bool print(const THD *, String *str, enum_query_type) const override {
    return !str->append(STRING_WITH_LEN("last_insert_ids()"));
  }

  bool walk(Item_processor, enum_walk, uchar *) override {
    return false;
  }

 private:
  List<Create_field> *get_field_list() override;

  bool do_init_args() override { return false; }

  List<Create_field> fields;
};

Table_function_last_insert_ids::~Table_function_last_insert_ids() {
  assert(fields.elements == 1);
  delete fields.head();
}

List<Create_field> *Table_function_last_insert_ids::get_field_list() {
  assert(fields.is_empty());

  auto *const field = new Create_field;
  field->init_for_tmp_table(MYSQL_TYPE_LONGLONG, MAX_BIGINT_WIDTH,
                            DECIMAL_NOT_SPECIFIED, /* is_nullable */ false,
                            /* is_unsigned */ true, 0, "insert_id");
  fields.push_back(field);

  return &fields;
}

bool Table_function_last_insert_ids::fill_result_table() {
  assert(!fields.is_empty());
  assert(!table->materialized);
  assert(table->s->fields == 1);

  empty_table();

  auto *const field = get_field(0);
  assert(field->field_index() == 0);
  field->store(current_thd->first_successful_insert_id_in_prev_stmt);
  field->set_notnull();
  write_row();

  return false;
}

Percona SEQUENCE_TABLE

After I have posted this, Percona's Yura Soroking pointed out on LinkedIn their implementation of SEQUENCE_TABLE function: blog post, the initial implementation source code. This implementation follows similar framework as the toy implementation above.

Tuesday, May 28, 2024

A MySQL 8.4.0 branch with patches

While writing the previous post, I noticed that I didn't have a central location for the patches that I submitted to Oracle. Some were in local branches, some were .patch files lying around. So now I pushed a tree that has all those patches applied in a single place: patched-mysql-8.4.0, and I even added a README. This tree hopefully will make it easier to rebase on future Oracle releases. I had maintained similar branches before while pushing some of the Percona patches to Oracle around early 8.0 times.

As for the patches themselves, the majority of them add various missing features for the clone plugin to be able to support more than one transactional storage engine. There is also a compilation fix and a slightly improved AddressSanitizer support patch.

All MySQL 8.4.0 users are advised to migrate ASAP! /s