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MDEV-36107: Proposal for Enhancements in MariaDB Operator Handling
by Harshit Vijay Kumar 02 Apr '25

02 Apr '25

Dear MariaDB Developer Community, I hope you are doing well. I am *Harshit Vijay Kumar*, a final-year undergraduate student in Computer Science. I have been researching *MDEV-36107 <https://jira.mariadb.org/browse/MDEV-36107>* for *GSoC 2025* and, during my exploration of operator operations in MariaDB, I came across some behaviors that caught my attention. To further investigate, I compared these behaviors with MySQL to understand their differences. *Observations: * *(1) Handling Large Number Multiplications Using Exponents* - Currently, multiplying two large integers results in an *overflow*, returning 0 instead of using an exponent-based representation. SELECT 18014398509481984 * 18014398509481984; *MariaDB Output:* 0 *SQL Output:* 3.2451855365842673e+32 - Interestingly, if one of the operands is a *floating-point number*, the result is computed without overflow: SELECT 18014398509481984 * 18014398509481984399405765456789087654390954.0; *Output:* 324518553658426733978210646499548233026655740664701555572736.0 - This inconsistency between integer-only and mixed-type operations is confusing. A standardized approach, possibly leveraging exponent notation, could improve clarity. *(2) Rounding Floating-Point Outputs* - MariaDB currently returns full precision in floating-point calculations, which can lead to unnecessary precision in practical use cases. SELECT 1.0376728938476536278903984765 + 1.039876453672890938476536278902345678908765434567890; *MariaDB Output:* 2.07754934752054456636693475540234567891 *SQL Output:* 2.077549347520544 - A rounding mechanism would allow for concise representation and reduce storage overhead, especially for users unaware of excessive precision in their datasets. *(3) Eliminating Unnecessary Zeros in Floating-Point Representation* SELECT 1.0000 * 1.0000000000; *MariaDB Output:* 1.00000000000000 - While useful in some cases, the inclusion of excessive trailing zeros unnecessarily increases storage usage. A more compact representation should be considered, where only *significant digits* are retained. *(4) Implementation of == Equality Operator* - Currently, MariaDB allows the *assignment operator (=)* for comparisons. However, since = is primarily used for assignments, this dual-purpose behavior can be confusing. - Proposal: Introduce a dedicated *== equality operator* for clear and intuitive comparisons across *INT, FLOAT, BOOL, and CHAR* types. - Expected behavior: - If values match → return 1 - If values don’t match → return 0 Testing & Next Steps To implement these improvements, I plan to add *test cases* in mysql-test covering all edge cases for these operators. I will follow the approach used in the following implementations: - func_equal.result <https://github.com/MariaDB/server/blob/main/mysql-test/main/func_equal.resu…> - func_equal.test <https://github.com/MariaDB/server/blob/main/mysql-test/main/func_equal.test> I would really appreciate your insights on these ideas. If any of these behaviors have intentional design choices, I would love to understand the rationale behind them. Looking forward to your feedback! Best Regards, Harshit Vijay Kumar

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Re: 0a0c5f349c6: MDEV-36425 Extend read_only to also block share locks and super user
by Sergei Golubchik 02 Apr '25

02 Apr '25

Hi, Monty, On Apr 01, Michael Widenius wrote: > revision-id: 0a0c5f349c6 (mariadb-11.8.1-42-g0a0c5f349c6) > parent(s): 21321025e5e > author: Michael Widenius > committer: Michael Widenius > timestamp: 2025-03-31 20:09:03 +0300 > message: > > MDEV-36425 Extend read_only to also block share locks and super user > > The main purpose of this allow one to use the --read-only > option to ensure that no one can issue a query that can > block replication. > > The --read-only option can now take 4 different values: > 0 No read only (as before). > 1 Blocks changes for users without the 'READ ONLY ADMIN' > privilege (as before). > 2 Blocks in addition LOCK TABLES and SELECT IN SHARE MODE > for not 'READ ONLY ADMIN' users. > 3 Blocks in addition 'READ_ONLY_ADMIN' users for all the > previous statements. > diff --git a/mysql-test/main/read_only.result b/mysql-test/main/read_only.result > index 65cc12ffce9..89390ad65d5 100644 > --- a/mysql-test/main/read_only.result > +++ b/mysql-test/main/read_only.result > @@ -69,11 +69,14 @@ set global read_only=1; > connection con1; > select @@global.read_only; > @@global.read_only > -0 > +OFF > unlock tables ; > +Timeout in wait_condition.inc for SELECT @@global.read_only= 1 > +Id User Host db Command Time State Info Progress > +5 test localhost test Query 0 starting show full processlist 0.000 Forgot to fix? It should wait for @@global.read_only='READ_ONLY' now > select @@global.read_only; > @@global.read_only > -1 > +READ_ONLY > connection default; > reap; > connection default; > diff --git a/sql/lock.cc b/sql/lock.cc > index 1296e5455d5..8f9f97f88b7 100644 > --- a/sql/lock.cc > +++ b/sql/lock.cc > @@ -179,19 +198,48 @@ lock_tables_check(THD *thd, TABLE **tables, uint count, uint flags) > > /* > Prevent modifications to base tables if READ_ONLY is activated. > - In any case, read only does not apply to temporary tables. > + In any case, read only does not apply to temporary tables or slave > + threads. > */ > - if (!(flags & MYSQL_LOCK_IGNORE_GLOBAL_READ_ONLY) && !t->s->tmp_table) > + if (unlikely(opt_readonly) && > + !(flags & MYSQL_LOCK_IGNORE_GLOBAL_READ_ONLY) && !t->s->tmp_table && > + !thd->slave_thread) > { > - if (t->reginfo.lock_type >= TL_FIRST_WRITE && > - !ignore_read_only && opt_readonly && !thd->slave_thread) > + switch (opt_readonly) // Impossible you have "Impossible" comment on a wrong line > { > - my_error(ER_OPTION_PREVENTS_STATEMENT, MYF(0), "--read-only"); > - DBUG_RETURN(1); > + case READONLY_OFF: > + DBUG_ASSERT(0); > + break; > + case READONLY_ON: // Compatibility > + if (!(thd->security_ctx->master_access & PRIV_IGNORE_READ_ONLY) && > + t->reginfo.lock_type >= TL_FIRST_WRITE) > + { > + mariadb_error_read_only(); > + DBUG_RETURN(1); I'd make mariadb_error_read_only() to return 1. Then you can write DBUG_RETURN(mariadb_error_read_only()); here and also in all other places, check it out, it's always followed by return 1. > + } > + break; > + case READONLY_NO_LOCK: > + if (!(thd->security_ctx->master_access & PRIV_IGNORE_READ_ONLY) && > + (thd->lex->sql_command == SQLCOM_LOCK_TABLES || > + t->reginfo.lock_type >= TL_FIRST_WRITE || > + t->reginfo.lock_type == TL_READ_WITH_SHARED_LOCKS)) may be t->reginfo.lock_type >= TL_READ_WITH_SHARED_LOCKS ? > + { > + mariadb_error_read_only(); > + DBUG_RETURN(1); > + } > + break; > + case READONLY_NO_LOCK_NO_ADMIN: > + if (thd->lex->sql_command == SQLCOM_LOCK_TABLES || > + t->reginfo.lock_type >= TL_FIRST_WRITE || > + t->reginfo.lock_type == TL_READ_WITH_SHARED_LOCKS) and here > + { > + mariadb_error_read_only(); > + DBUG_RETURN(1); > + } > + break; > } > } > } > - > /* > Locking of system tables is restricted: > locking a mix of system and non-system tables in the same lock > diff --git a/sql/sql_class.h b/sql/sql_class.h > index d65cec37154..34ee8391009 100644 > --- a/sql/sql_class.h > +++ b/sql/sql_class.h > @@ -3448,9 +3452,12 @@ class THD: public THD_count, /* this must be first */ > */ > inline bool is_read_only_ctx() rename to, for example, check_read_only_with_errror() > { > - return opt_readonly && > - !(security_ctx->master_access & PRIV_IGNORE_READ_ONLY) && > - !slave_thread; > + if (likely(!opt_readonly) || slave_thread || > + ((security_ctx->master_access & PRIV_IGNORE_READ_ONLY) && > + opt_readonly != READONLY_NO_LOCK_NO_ADMIN)) > + return false; > + mariadb_error_read_only(); > + return true; > } > > private: > diff --git a/sql/sys_vars.cc b/sql/sys_vars.cc > index 0247afd91a6..545b4674da1 100644 > --- a/sql/sys_vars.cc > +++ b/sql/sys_vars.cc > @@ -3253,15 +3253,24 @@ static bool fix_read_only(sys_var *self, THD *thd, enum_var_type type) > transition (especially when transitioning from false to true) and > synchronizes both booleans in the end. > */ > -static Sys_var_on_access_global<Sys_var_mybool, > + > +const char *read_only_mode_names[]= > +{"OFF", "READ_ONLY", "READ_ONLY_NO_LOCK", "READ_ONLY_NO_LOCK_NO_ADMIN"}; > + > +static Sys_var_on_access_global<Sys_var_enum, > PRIV_SET_SYSTEM_GLOBAL_VAR_READ_ONLY> > Sys_readonly( > "read_only", > - "Make all non-temporary tables read-only, with the exception for " > - "replication (slave) threads and users with the 'READ ONLY ADMIN' " > - "privilege", > - GLOBAL_VAR(read_only), CMD_LINE(OPT_ARG), DEFAULT(FALSE), > - NO_MUTEX_GUARD, NOT_IN_BINLOG, > + "Do not allow changes to non-temporary tables. Options are:" > + "OFF changes allowed. " > + "READ_ONLY blocks changes for users without the 'READ ONLY ADMIN' " "Disallow changes for users without the READ ONLY ADMIN privilege" > + "privilege. " > + "READ_ONLY_NO_LOCK blocks in addition LOCK TABLES and " > + "SELECT IN SHARE MODE for not ADMIN users. " "Additionally disallows LOCK TABLES and SELECT IN SHARE MODE" > + "READ_ONLY_NO_LOCK_NO_ADMIN blocks in addition 'ADMIN' users. " "Disallows also for users with READ_ONLY ADMIN privilege" > + "Replication (slave) threads are not affected by this option", > + GLOBAL_VAR(read_only), CMD_LINE(OPT_ARG), > + read_only_mode_names, DEFAULT(0), NO_MUTEX_GUARD, NOT_IN_BINLOG, > ON_CHECK(check_read_only), ON_UPDATE(fix_read_only)); > > // Small lower limit to be able to test MRR Regards, Sergei Chief Architect, MariaDB Server and security(a)mariadb.org

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Inquiry About GSoC 2025 and Proposal Submission
by Harsh Gupta 31 Mar '25

31 Mar '25

*Dear MariaDB Developers,* I hope you are doing well. My name is *Harsh Gupta*, and I am a *second-year B.Tech Computer Science and Design student at Madhav Institute of Technology and Science, Gwalior*. I am passionate about databases and open-source development, and I am eager to contribute to MariaDB through *Google Summer of Code 2025*. I have gone through the project ideas listed for GSoC and found the MDEV-28395 <https://jira.mariadb.org/browse/MDEV-28395> LOAD DATA plugins particularly interesting. I have experience with *C++ and database systems*, and I have been exploring MariaDB’s codebase to get familiar with its architecture. I have prepared a draft proposal outlining my approach to this project, including my implementation plan and timeline. I would appreciate your feedback to refine it further before submitting it officially. Could you please review my proposal and provide any suggestions for improvement? Also, I would love to connect with potential mentors to discuss the project's scope and feasibility. Looking forward to your guidance and feedback! Best regards, *Harsh Gupta* 📧 harshgupta9329(a)gmail.com

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Re: b7dbe187b1a: MDEV-34680 Asynchronous and Buffered Logging for Audit Plugin.
by Sergei Golubchik 31 Mar '25

31 Mar '25

Hi, Alexey, See few comments below. But the main question, could you have used FILE or IO_CACHE instead of a custom implementation? On Mar 08, Alexey Botchkov wrote: > revision-id: b7dbe187b1a (mariadb-11.8.1-8-gb7dbe187b1a) > parent(s): 6f1161aa34c > author: Alexey Botchkov > committer: Alexey Botchkov > timestamp: 2025-03-02 16:27:23 +0400 > message: > > MDEV-34680 Asynchronous and Buffered Logging for Audit Plugin. > > Buffering added to the file logger. > Two buffers are created so writing to the file doesn't > block other threads from logging. > Operations isolated with two mutexes. > diff --git a/include/mysql/service_logger.h b/include/mysql/service_logger.h > index 35c2eb1e3a9..adce7bc9038 100644 > --- a/include/mysql/service_logger.h > +++ b/include/mysql/service_logger.h > @@ -64,41 +64,44 @@ extern struct logger_service_st { > void (*logger_init_mutexes)(); > LOGGER_HANDLE* (*open)(const char *path, > unsigned long long size_limit, > - unsigned int rotations); > + unsigned int rotations, size_t buffer_size); incompatible API change. MUST change the major service version. > int (*close)(LOGGER_HANDLE *log); > int (*vprintf)(LOGGER_HANDLE *log, const char *fmt, va_list argptr) > ATTRIBUTE_FORMAT_FPTR(printf, 2, 0); > int (*printf)(LOGGER_HANDLE *log, const char *fmt, ...) > ATTRIBUTE_FORMAT_FPTR(printf, 2, 3); > - int (*write)(LOGGER_HANDLE *log, const char *buffer, size_t size); > + int (*write)(LOGGER_HANDLE *log, const void *data, size_t size); > int (*rotate)(LOGGER_HANDLE *log); > + int (*sync)(LOGGER_HANDLE *log); > } *logger_service; > > #ifdef MYSQL_DYNAMIC_PLUGIN > > #define logger_init_mutexes logger_service->logger_init_mutexes > -#define logger_open(path, size_limit, rotations) \ > - (logger_service->open(path, size_limit, rotations)) > +#define logger_open(path, size_limit, rotations, buffer_size) \ > + (logger_service->open(path, size_limit, rotations, buffer_size)) > #define logger_close(log) (logger_service->close(log)) > #define logger_rotate(log) (logger_service->rotate(log)) > +#define logger_rsync(log) (logger_service->sync(log)) > #define logger_vprintf(log, fmt, argptr) (logger_service->\ > vprintf(log, fmt, argptr)) > #define logger_printf (*logger_service->printf) > -#define logger_write(log, buffer, size) \ > - (logger_service->write(log, buffer, size)) > +#define logger_write(log, data, size) \ > + (logger_service->write(log, data, size)) > #else > > void logger_init_mutexes(); > LOGGER_HANDLE *logger_open(const char *path, > unsigned long long size_limit, > - unsigned int rotations); > + unsigned int rotations, size_t buffer_size); > int logger_close(LOGGER_HANDLE *log); > int logger_vprintf(LOGGER_HANDLE *log, const char *fmt, va_list argptr) > ATTRIBUTE_FORMAT(printf, 2, 0); > int logger_printf(LOGGER_HANDLE *log, const char *fmt, ...) > ATTRIBUTE_FORMAT(printf, 2, 3); > - int logger_write(LOGGER_HANDLE *log, const char *buffer, size_t size); > + int logger_write(LOGGER_HANDLE *log, const void *data, size_t size); > int logger_rotate(LOGGER_HANDLE *log); > + int logger_sync(LOGGER_HANDLE *log); > #endif > > > diff --git a/mysys/file_logger.c b/mysys/file_logger.c > index a753c049f68..5464e43eddf 100644 > --- a/mysys/file_logger.c > +++ b/mysys/file_logger.c > @@ -145,85 +230,108 @@ static int do_rotate(LOGGER_HANDLE *log) > namebuf[log->path_len]= 0; > result= my_rename(namebuf, logname(log, log->path, 1), MYF(0)); > log->file= my_open(namebuf, LOG_FLAGS, MYF(0)); > + log->in_file= 0; > exit: > errno= my_errno; > return log->file < 0 || result; > } > > > -/* > - Return 1 if we should rotate the log > -*/ > - > -my_bool logger_time_to_rotate(LOGGER_HANDLE *log) > -{ > - my_off_t filesize; > - if (log->rotations > 0 && > - (filesize= my_tell(log->file, MYF(0))) != (my_off_t) -1 && > - ((ulonglong) filesize >= log->size_limit)) > - return 1; > - return 0; > -} > - > - > int logger_vprintf(LOGGER_HANDLE *log, const char* fmt, va_list ap) > { > - int result; > char cvtbuf[1024]; > size_t n_bytes; > > - flogger_mutex_lock(&log->lock); > - if (logger_time_to_rotate(log) && do_rotate(log)) > - { > - result= -1; > - errno= my_errno; > - goto exit; /* Log rotation needed but failed */ > - } > - > n_bytes= my_vsnprintf(cvtbuf, sizeof(cvtbuf), fmt, ap); > if (n_bytes >= sizeof(cvtbuf)) > n_bytes= sizeof(cvtbuf) - 1; > > - result= (int)my_write(log->file, (uchar *) cvtbuf, n_bytes, MYF(0)); > - > -exit: > - flogger_mutex_unlock(&log->lock); > - return result; > + return logger_write(log, cvtbuf, n_bytes); > } > > > -static int logger_write_r(LOGGER_HANDLE *log, my_bool allow_rotations, > - const char *buffer, size_t size) > +int logger_write(LOGGER_HANDLE *log, const void *data, size_t size) > { > int result; > + size_t in_buffer; > + > + mysql_mutex_lock(&log->lock); > > - flogger_mutex_lock(&log->lock); > - if (allow_rotations && logger_time_to_rotate(log) && do_rotate(log)) > + if (log->buffer_left >= size) > + { > + memcpy(log->buffer_pos, data, size); > + log->buffer_pos+= size; > + log->buffer_left-= size; > + mysql_mutex_unlock(&log->lock); > + return size; > + } > + > + mysql_mutex_lock(&log->lock_buffer); > + > + in_buffer= log->buffer_pos - log->buffer; > + > + { /* swap buffers. */ > + uchar *tmp_buf= log->buffer; > + log->buffer= log->idle_buffer; > + log->idle_buffer= tmp_buf; > + } > + > + set_buffer_pos_and_left(log); > + > + /* Now other threads can write to the new buffer. */ > + mysql_mutex_unlock(&log->lock); > + > + if ((in_buffer && > + my_write(log->file, log->idle_buffer, in_buffer, MYF(0)) != in_buffer)|| > + my_write(log->file, (uchar *) data, size, MYF(0)) != size) > { > result= -1; > errno= my_errno; > - goto exit; /* Log rotation needed but failed */ > + goto exit_buf; > } > + else > + result= 0; > > - result= (int)my_write(log->file, (uchar *) buffer, size, MYF(0)); > + log->in_file+= in_buffer + size; > + if (log->rotations > 0 && log->in_file >= log->size_limit) > + { > + if (do_rotate(log)) > + { > + result= -1; > + errno= my_errno; > + goto exit_buf; /* Log rotation needed but failed */ > + } > + } > > -exit: > - flogger_mutex_unlock(&log->lock); > +exit_buf: > + mysql_mutex_unlock(&log->lock_buffer); > return result; > } > > > -int logger_write(LOGGER_HANDLE *log, const char *buffer, size_t size) > -{ > - return logger_write_r(log, TRUE, buffer, size); > -} > - > int logger_rotate(LOGGER_HANDLE *log) > { > int result; > - flogger_mutex_lock(&log->lock); > - result= do_rotate(log); > - flogger_mutex_unlock(&log->lock); > + mysql_mutex_lock(&log->lock); > + mysql_mutex_lock(&log->lock_buffer); > + result= flush_buffer(log) || do_rotate(log); I'd though you can switch buffers here too and flush/rotate only under the lock_buffer mutex > + mysql_mutex_unlock(&log->lock_buffer); > + mysql_mutex_unlock(&log->lock); > + return result; > +} > + > + > +int logger_sync(LOGGER_HANDLE *log) Why did you introduce an explicit sync API? > +{ > + int result; > + mysql_mutex_lock(&log->lock); > + mysql_mutex_lock(&log->lock_buffer); > + if ((result= flush_buffer(log))) > + { > + result= fsync(log->file); > + } > + mysql_mutex_unlock(&log->lock_buffer); > + mysql_mutex_unlock(&log->lock); > return result; > } > > diff --git a/plugin/server_audit/server_audit.c b/plugin/server_audit/server_audit.c > index 5fc0e3373f3..e51df7ab6b5 100644 > --- a/plugin/server_audit/server_audit.c > +++ b/plugin/server_audit/server_audit.c > @@ -1393,26 +1401,15 @@ static void change_connection(struct connection_info *cn, > static int write_log(const char *message, size_t len, int take_lock) > { > int result= 0; > + > if (take_lock) > - { > - /* Start by taking a read lock */ > mysql_prlock_rdlock(&lock_operations); > - } > > if (output_type == OUTPUT_FILE) > { > if (logfile) > { > - my_bool allow_rotate= !take_lock; /* Allow rotate if caller write lock */ > - if (take_lock && logger_time_to_rotate(logfile)) > - { > - /* We have to rotate the log, change above read lock to write lock */ > - mysql_prlock_unlock(&lock_operations); > - mysql_prlock_wrlock(&lock_operations); > - allow_rotate= 1; > - } > - if (!(is_active= (logger_write_r(logfile, allow_rotate, message, len) == > - (int) len))) > + if (!(is_active= (logger_write(logfile, message, len) == (int) len))) nice, rotation is indeed the logger's headache, not the caller's > { > ++log_write_failures; > result= 1; > @@ -2899,6 +2906,36 @@ static void update_file_rotations(MYSQL_THD thd __attribute__((unused)), > } > > > +static void update_file_buffer_size(MYSQL_THD thd __attribute__((unused)), > + struct st_mysql_sys_var *var __attribute__((unused)), > + void *var_ptr __attribute__((unused)), const void *save) > +{ > + file_buffer_size= *(unsigned int *) save; > + > + error_header(); > + fprintf(stderr, "Log file buffer size was changed to '%d'.\n", file_buffer_size); > + > + if (!logging || output_type != OUTPUT_FILE) > + return; > + > + ADD_ATOMIC(internal_stop_logging, 1); > + if (!maria_55_started || !debug_server_started) > + mysql_prlock_wrlock(&lock_operations); > + > + stop_logging(); > + if (start_logging()) this could be an API call in the logger. Like "reinit(new params)" and it'll close, change params, open - all under a log mutex, which doesn't need to be destroyed and reinitialized. > + { > + error_header(); > + fprintf(stderr, "Logging was disabled..\n"); > + CLIENT_ERROR(1, "Logging was disabled.", MYF(ME_WARNING)); > + } > + > + if (!maria_55_started || !debug_server_started) > + mysql_prlock_unlock(&lock_operations); > + ADD_ATOMIC(internal_stop_logging, -1); > +} > + > + > static void update_file_rotate_size(MYSQL_THD thd __attribute__((unused)), > struct st_mysql_sys_var *var __attribute__((unused)), > void *var_ptr __attribute__((unused)), const void *save) Regards, Sergei Chief Architect, MariaDB Server and security(a)mariadb.org

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Introduction & Interest in GSoC 2025 with MariaDB
by H.NAVEENKUMAR 30 Mar '25

30 Mar '25

*Hello MariaDB Developers,* I hope you're all doing well. My name is *Naveen Kumar*, and I am currently a student with a strong interest in open-source development, databases, and backend engineering. I have experience working with *Python, JavaScript, MySQL, MongoDB, and full-stack development*. I recently registered for *Google Summer of Code (GSoC) 2025* with MariaDB and am eager to contribute to the project. I am still exploring the available project ideas and would appreciate guidance on how to choose the best fit based on my skills. It would be great if mentors or experienced contributors could suggest beginner-friendly issues or key areas to focus on while getting familiar with the MariaDB codebase. Looking forward to learning, collaborating, and making meaningful contributions to the community! Best regards, *Naveen Kumar*

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MariaDB 11.8.1 in Debian
by Otto Kekäläinen 23 Mar '25

23 Mar '25

Hi, I just wanted to let you know that MariaDB 11.8.1 just landed in Debian testing, which will be the upcoming Debian 13 "Trixie" release. I will continue with various quality assurance tasks so that eventually when 11.8.2 comes out it will be as polished as possible from Debian/Ubuntu perspective. Hopefully .2 does not have any big changes, but just bug fixes.

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Prepared statements analytics problem
by Dmitrii Kochetov 19 Mar '25

19 Mar '25

Most database monitoring systems, such as Newrelic, Datadog, Dolphie, Ottertune, Releem, Solarwinds, use data from the performance_schema database from the events_statements_summary_by_digest and events_statements_* tables to get query analytics for databases. This information allows to calculate system performance metrics, in particular Latency. Also, the data from these tables allows you to get a complete picture of the database operation - what queries are executed, their execution statistics, to get query templates based on digest_text, and based on SQL_TEXT field from events_statements_* or QUERY_SAMPLE_TEXT from events_statements_summary_by_digest (for MySQL >= 8) to get a sample query for digest and optimize it. The prepared statements analytics are contained in a single table prepared_statements_instances, which is managed by Performance_schema as follows: - Statement preparation If the statement is successfully instrumented, a new row is added to the prepared_statements_instances table. If the statement cannot be instrumented, Performance_schema_prepared_statements_lost status variable is incremented. - Prepared statement execution Execution of a EXECUTE command for an instrumented prepared statement instance updates the corresponding prepared_statements_instances table row. - Prepared statement deallocation Execution of a CLOSE command for an instrumented prepared statement instance removes the corresponding prepared_statements_instances table row. To avoid resource leaks, removal occurs even if the prepared statement instruments described previously are disabled. In this regard, there are the following problems with analytics for prepared statements compared to regular queries: 1) Most applications work with prepared statements using the following method when processing a single query - creating a prepared statement, executing the prepared statement, and then dropping the prepared statement. This leads to the fact that query statistics exist for a very short period of time, during which it may not be possible to fetch them. 2) The second problem of prepared statement analytics in comparison with regular queries is the absence of the query hash (digest) and information about the schema_name in which the prepared statement is executed, which makes it difficult to identify unique queries, since a separate record in the Prepared_Statements_instances table is created for each creation of a prepared statement. 3) Execution of prepared statements is possible in two protocols: Binary and text. Execution of a prepared statement in the binary protocol does not create an entry in the events_statements_* tables, but execution in the text protocol creates an entry in the specified tables, which leads to different behaviors of the same prepared statement but in different protocols. 4) For prepared statements, there is no option in getting an example request without a ? placeholder. The SQL_TEXT field in Prepared_Statements_instances contains The prepared statement text, with ? placeholder markers, and in some cases (when executing in the text protocol) it is possible to find only the execute command of this statement, which further requires mapping ? placeholder markers with parameters from the execute request. But there are limitations that the binary protocol does not store EXECUTE requests for prepared statements, and most of the interactions with the database occur through it, through drivers for different programming languages, and another limitation may be the use of variables in the EXECUTE command, the value of which still needs to be obtained. Proposed solution: 1) Records should not be deleted from the Prepared_Statements_instances table after dropping prepared statements. If the table is full, the counter Performance_schema_prepared_statements_lost and If no row has the statement digest value for the statement that just completed, and the table is full, the statistics for the statement that just completed are added to a special “catch-all” row with DIGEST = NULL, which is created if necessary. 2) Each statement must be unique by the fields schema_name, in which the given statement is executed and its hash, digest, which will be the same for the same prepared statement. 3) In the tables events_statements_* must be recorded information about the fact of PREPARE, EXECUTE and DEALLOCATE execution for prepared statement, where in the DIGEST_TEXT field is stored the call of the execute command, and in SQL_TEXT - the normalized prepared query, in which ? placeholder markers are replaced by concrete values.

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MariaDB 11.8(.1) to Debian
by Otto Kekäläinen 15 Mar '25

15 Mar '25

Hi, Just FYI, I am done with the February maintenance releases to Debian and Ubuntu, and this weekend started working on importing MairaDB 11.8(.1) to Debian. Draft is visible at https://salsa.debian.org/mariadb-team/mariadb-server/-/merge_requests/107

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Using GitHub directly from inside Emacs
by Otto Kekäläinen 15 Mar '25

15 Mar '25

Hi! I don't use Emacs myself, but I learned last weekend at FOSDEM that some Emacs users love using the Emacs extension Magit [1] with the Forge [2] feature to list and review GitHub Pull Requests directly from Emacs without opening a browser. Just curious to know if any Emacs users here (Monty?) have tried Magit for interacting with https://github.com/MariaDB/server/pulls? There are currently 240 open PRs and 157 have zero reviews [3] from people with GitHub permissions to give reviews. To get more contributors, we need to have more people participating in reviewing/approving incoming contributions. Also some parts of the contributions process are not very optimal, and the process is likely to become smoother only if enough of current core developers at least occasionally "eat their own cooking" and experience (at least parts) of the contribution process. - Otto [1] https://magit.vc/ [2] https://magit.vc/manual/forge.html [3] https://github.com/MariaDB/server/pulls?q=is%3Apr+is%3Aopen+review%3Anone

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Review of MDEV-35915 Implement Global temporary tables, part 2
by Michael Widenius 12 Mar '25

12 Mar '25

Review of Global temporary tables, part 2 commit a9478ca44b44118cf70de493569d64afbb5cd925 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Fri Nov 22 02:15:56 2024 +0100 Fix deallocation of Sql_cmd_dml::result Made as a part of MDEV-34309 Sql_cmd_dml::result is using mem_root to control memory allocation, but Sql_alloc allows to mark the memory as freed via destructor. Normal runs have DTRACE disabled, so accesses in MYSQL_DML_DONE are turned into no-op, and that is the bug is not shown. Enabling DTRACE brings a crash yet in a bootstrap. The fix is to carefully set Sql_cmd_dml::result to nullptr whenever it is freed, or is marked as freed. Please include the title of MDEV-354309 in the commit description @@ -34253,6 +34253,7 @@ bool Sql_cmd_dml::prepare(THD *thd) MYSQL_DML_START(thd); + result= nullptr; // It could've been set since the last run. lex->context_analysis_only|= CONTEXT_ANALYSIS_ONLY_DERIVED; if (open_tables_for_query(thd, lex->query_tables, &table_count, 0, How +++ b/sql/sql_delete.cc @@ -1882,6 +1882,7 @@ bool Sql_cmd_delete::execute_inner(THD *thd) { select_result *sel_result= NULL; delete result; + result= nullptr; /* This is DELETE ... RETURNING. It will return output to the client */ if (thd->lex->analyze_stmt) { @@ -1929,10 +1930,7 @@ bool Sql_cmd_delete::execute_inner(THD *thd) } if (result) - { res= false; - delete result; - } Why remove the delete. If the delete may free wrong things, then the newly added result is also likely to free wrong things. Anyway, the code is clearly wrong here. One cannot set res to 0 if res is 1. This means we are ignoring a possible error from the upper level (probably OOM) and we are probably going to assert later in the code that checks if we can send ok. Try to remove the seteting of res= false and run mtr. Same logics goes for all changes in Sql_cmd_update::execute_inner(THD *thd diff --git a/sql/sql_update.cc b/sql/sql_update.cc if (unlikely(res)) + if (unlikely(res) && result) result->abort_result_set(); else { The above is wrong. Should be: + if (unlikely(res)) { if (result) result->abort_result_set(); } else { As otherwise you may call send_explain() when you shouldn't ------------------ Suggestion: - Move delete of result to unprepare. This will ensure that result is always 0 on Sql_cmd_dml::prepare() and excute_innert and you can replace delete result with 'DBUG_ASSERT(result == 0)' in most of your changes. - Remove setting res= 0 if we have a result and check with mtr. Conclusion: - As this is not cricial and you are going on vacation, I will take over this issue --------- commit 6a000835f5f58aba221ab89c120adae4be16abf3 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Thu Feb 20 16:12:37 2025 +0100 fix show create diff --git a/sql/sql_show.cc b/sql/sql_show.cc index da0081fd1f8..201aa8e3110 100644 --- a/sql/sql_show.cc +++ b/sql/sql_show.cc @@ -1413,8 +1413,13 @@ mysqld_show_create(THD *thd, TABLE_LIST *table_list) if (table_list->table && table_list->table->s->tmp_table != NO_TMP_TABLE) { TMP_TABLE_SHARE *share= (TMP_TABLE_SHARE*)table_list->table->s; - if (share->from_share && table_list->table->file->records() == 0) - thd->drop_temporary_table(table_list->table, NULL, true); + if (share->from_share) + { + if (table_list->table->file->info(HA_STATUS_VARIABLE) + || (table_list->table->file->records() == 0 + && thd->drop_temporary_table(table_list->table, NULL, true))) + error= TRUE; + } Please move || and && to previous lines so we have the test lined up nicely in the editor. This is how most of the MariaDB code is written. commit 55ff0fb18bbe4539db27ea73cc2b795e53521772 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Thu Feb 20 16:12:49 2025 +0100 add rpl assertions if (thd->temporary_tables - && thd->temporary_tables->global_temporary_tables_count) // TODO this may be buggy on slave + && thd->temporary_tables->global_temporary_tables_count) { move && up to previous line. @@ -6051,6 +6053,7 @@ my_bool open_global_temporary_table(THD *thd, TABLE_SHARE *source, if (thd->mdl_context.clone_ticket(&share->mdl_request)) return TRUE; table->reginfo.lock_type= TL_IGNORE; + share->table_creation_was_logged= 1; } The above means that we assume that slave have the same global temporary table, which is probably not the case. Better to set share->table_creation_was_logged=0 for the local temporary tables we are creating which means that any update of the table through the GTT will use row based replication. Please also add a function comment before my_bool open_global_temporary_table(THD *thd, TABLE_SHARE *source, TABLE_LIST *out_table, MDL_ticket *mdl_ticket) commit a64bbaf483ad714493db401f68049ce85a886c96 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Thu Feb 27 01:07:45 2025 +0100 CREATE: use frm header to store GTT bits diff --git a/sql/temporary_tables.cc b/sql/temporary_tables.cc index 45bca833d17..ea46c4035ba 100644 --- a/sql/temporary_tables.cc +++ b/sql/temporary_tables.cc @@ -1324,10 +1324,10 @@ int THD::commit_global_tmp_tables() All_share_tables_list::Iterator tables_it(share->all_tmp_tables); TABLE *table= tables_it++; DBUG_ASSERT(table); - if (!share->on_commit_delete) + if (!share->on_commit_delete()) table->file->info(HA_STATUS_VARIABLE); // update records() stat - if (share->on_commit_delete || table->file->records() == 0) + if (share->on_commit_delete() || table->file->records() == 0) error= drop_tmp_table_share(share, NULL, true); } I still think it would be better to not drop the temporary file based on file->records(). The reason is that some temporary table will be slow to drop and if there are users that is using these for many queries things will be slower than they need to be. - Not critical, can be discussed and changed later. commit 21f9ac1e56d6c81a431e5bdbc9b6b89c8b565ca2 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Thu Feb 27 01:12:34 2025 +0100 minor (typo, style) fixes -struct Closefrm_context +static my_bool open_gtt_on_error(TABLE *table) { - TABLE *table; - ~Closefrm_context() { closefrm(table); } -}; + closefrm(table); + return TRUE; +} Change return to void as this should never fail. Yes, it will require a few changes in callers, but it better to do return TRUE; in the caller than have the reviewer have to look at what another function is returning. +++ b/sql/temporary_tables.cc @@ -329,7 +329,9 @@ bool THD::internal_open_temporary_table(TABLE_LIST *tl, TABLE **table, { if (tmp_share->from_share && sql_command_flags() & (CF_ADMIN_COMMAND |CF_SCHEMA_CHANGE)) - DBUG_RETURN(false); + DBUG_RETURN(false); /* We want to use real global temporary table + when ALTER/DROP is executed. + */ Move the comment before the DBUG_RETURN() commit 9e1f5413f619bf4f88eef0f0a50fb7df4b8e7d44 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Sat Mar 1 01:27:04 2025 +0100 fix ALTER TABLE long wait @@ -11676,7 +11677,7 @@ do_continue:; */ if (alter_info->requested_lock != Alter_info::ALTER_TABLE_LOCK_EXCLUSIVE && thd->mdl_context.upgrade_shared_lock(mdl_ticket, MDL_SHARED_NO_WRITE, - lock_wait_timeout)) + thd->variables.lock_wait_timeout)) goto err_new_table_cleanup; Add a comment why we should not use lock_wait_timeout here. This is needed as we are using it a few lines above and it is important for coders to know why the value is not reused here. commit f7629d745fe729ea445688f5b710a97108da7c76 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Sat Mar 1 02:09:20 2025 +0100 Don't drop local data tables for ON COMMIT PRESERVE when records()==0 connect con1,localhost,root,,; +insert t values(1); +connection default; +alter table t add j int; +ERROR HY000: Lock wait timeout exceeded; try restarting transaction +set statement lock_wait_timeout=0 for drop table t; +ERROR HY000: Lock wait timeout exceeded; try restarting transaction We have to add better error messages for known cases. "Cannot alter global temporary tables as we have open instances of it" "Cannot alter global temporary tables as there are other users for it" Can be done after vacation. diff --git a/mysql-test/main/global_temporary_table.test b/mysql-test/main/global_temporary_table.test index 0edc6eee493..17195eaf3ea 100644 --- a/mysql-test/main/global_temporary_table.test +++ b/mysql-test/main/global_temporary_table.test +--} insert into t1 values(1, 'one'); + select * from t1; No reason for having an extra empty line here. This commit is using: bool THD::use_real_global_temporary_share() const { return (sql_command_flags() & (CF_ALTER_TABLE | CF_SCHEMA_CHANGE | CF_STATUS_COMMAND) && lex->sql_command != SQLCOM_CREATE_TABLE) || lex->sql_command == SQLCOM_CREATE_VIEW; } Please add a comment and move |, && and || to the end of lines. Please also fix the indentation. You can also add a new flag CF_USE_LOCAL_GTT table and mark those commands for which using GTT will open a local GTT copy. In sql_show.cc:get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond) there is this code: if (thd->use_real_global_temporary_share()) continue; This looks wrong. We are ignoring all temporary tables if the above case is true. To ignore GTT ables we have to verify that the found share is a GTT table. Shouldn't we also test for tmp_share->from_share ? Why are we testing for use_real_global_temporary_share() in this code? This is called only be DML. Shouldn't that be safe for GTT tables? For what commands are thd->use_real_global_temporary_share() not true here? commit 718afd78dae4a37ed009ab349dfe9bca68fbc3d7 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Tue Mar 4 18:30:07 2025 +0100 Extract THD::has_open_global_temporary_tables() No comments commit cc35b9cb54e74a2f0fbbf4a2400599c7fddb750d Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Tue Mar 4 21:01:07 2025 +0100 Add CF_ALTER_TABLE No comments commit 381243f4e75f61a31305c656f9b6be20cec042d2 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Wed Mar 5 00:18:42 2025 +0100 add global_temporary_tables plugin, move relevant code to temporary_tables.cc + MariaDB_PLUGIN_MATURITY_STABLE Should probably not be stable ;) Please change to BETA. We just have to ensure that this does not cause problems in Jenkin. If it does, you can change it to GAMMA or STABLE (depending on what Jenkins supports) commit a7fa6f835998bc33f1528420df5fe3f1b8a5dbfd Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Wed Mar 5 00:50:50 2025 +0100 refactor drop_tmp_table_share + while ((tab= it++)) { + if (tab != table && tab->query_id != 0) + { + /* Found a table instance in use. This table cannot be dropped. */ + my_error(ER_CANT_REOPEN_TABLE, MYF(0), table->alias.c_ptr()); + result= true; + goto end; + } Suggested comment change: /* Found a table instance in use. This table cannot be dropped. */ -> /* Found a table instance in use (query_id != 0). This table cannot be dropped. */ ------- commit bb9ff1b2ec45b437bd39b6dacef8885fadeb818b Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Wed Mar 5 02:51:23 2025 +0100 refactor THD::internal_open_temporary_table No comments commit 72914bfd92ae7390f8e7924944c92a1dc9591e1a Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Wed Mar 5 22:06:02 2025 +0100 enforce limitations + if (create_info->table_options & HA_OPTION_GLOBAL_TEMPORARY_TABLE) + { + const char *error= NULL; + for (const Key &fk: create_info->alter_info->key_list) + if (fk.type == Key::FOREIGN_KEY) + { + error= "FOREIGN KEY"; + break; + } You can replace the above loop with: if (thd->lex->alter_info_flags & ALTER_ADD_FOREIGN_KEY) Note also that in your old code, later errors could overwrite earlier ones. Changing this to a normal if, like the others, will solve that. commit a2831f8e8efcfecd548b8ced6e19c3fc4d6966f9 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Thu Mar 6 20:55:00 2025 +0100 information_schema support mysql-test/main/global_temporary_table.result +GLOBAL TEMPORARY +show table status where temporary='Y'; +Name Engine Version Row_format Rows Avg_row_length Data_length Max_data_length Index_length Data_free Auto_increment Create_time Update_time Check_time Collation Checksum Create_options Comment Max_index_length Temporary Please add a test that show the output from information_schema.tables for all fields that are stable for mtr. By the way, why does the above show table status not show any data while +select TABLE_TYPE from information_schema.tables where table_name = 't1'; +TABLE_TYPE +TEMPORARY +GLOBAL TEMPORARY Show two rows just above show table status; At least 'TEMPORARY' should have 'Temporary' set to 'Y'' commit a580c6bc85791829c850d7eedc03d62a5ee99ffd Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Thu Mar 6 23:43:38 2025 +0100 VIEW support Views already open the correct tables automatically, so it just works. Almost ;) + || lex->sql_command == SQLCOM_CREATE_VIEW ; .... commit d4c00419ebb39a07f87eabf0eee3660a768cbbed Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Fri Mar 7 02:16:23 2025 +0100 AS SELECT support + if (table->s->tmp_table && + table->s->db_create_options & + (HA_OPTION_GLOBAL_TEMPORARY_TABLE|HA_OPTION_ON_COMMIT_DELETE_ROWS)) + table= NULL; // It will be deleted on commit + This will not work because of the following code: if (WSREP(thd) && table->file->ht->db_type == DB_TYPE_INNODB) You either have to add a goto or fix all references to 'table'. Note this code later in the same function. if (m_plock) { MYSQL_LOCK *lock= *m_plock; *m_plock= NULL; m_plock= NULL; if (create_info->pos_in_locked_tables) { /* If we are under lock tables, we have created a table that was originally locked. We should add back the lock to ensure that all tables in the thd->open_list are locked! */ table->mdl_ticket= create_info->mdl_ticket; This should be safe as long as on cannot use LOCK TABLES on gtt tables. Please add a check for that! Another thing to check is with GALERA that local gtt tables are not replicated. commit 45e2f14bcbdd61c1ea5712f5b79b07a096aa46d2 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Mon Mar 10 20:16:16 2025 +0100 CREATE TABLE ... LIKE support sql_table.cc: local_create_info.table_options&= ~HA_OPTIONS_TO_RESET_CREATE_LIKE; Looking at the code, I belive the above is always 0 here. Please replace with DBUG_ASSERT(local_create_info.table_options == 0); commit 1c44e4dabe22555a3b517db7f67c1e4d8b03fc70 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Mon Mar 10 21:49:11 2025 +0100 RENAME support +++ b/sql/sql_parse.cc @@ -6351,6 +6351,13 @@ check_rename_table(THD *thd, TABLE_LIST *first_table, check_grant(thd, INSERT_ACL | CREATE_ACL, &new_list, FALSE, 1, FALSE))) return 1; + + if (table->table && + table->table->s->db_create_options & HA_OPTION_GLOBAL_TEMPORARY_TABLE) + { + my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0)); + return 1; + } We need a better error here. Something like: "Cannot rename a global temporary tables as this connection has open instances of it" commit b0f02644c22522c325bfbddd847030d61237b4e8 Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Tue Mar 11 00:48:11 2025 +0100 FLUSH support, forbid LOCK FLUSH TABLE on Global temporary table is basically no-op, since it never has open instances. - It is ok to ignore flush table on GTT tables. There is no point in doing that. Same goes for temporary tables. +/** + Check if any global temporary tables are still opened in this session. +*/ +static int flush_check_for_global_temporary_tables(THD *thd, TABLE_LIST *tl) +{ + if (thd->rgi_slave || !thd->has_open_global_temporary_tables()) + return 0; + + for (;tl; tl= tl->next_global) + { + TABLE_SHARE *share= thd->find_tmp_table_share(tl); + if (share && share->db_create_options & HA_OPTION_GLOBAL_TEMPORARY_TABLE) + { + my_error(ER_LOCK_WAIT_TIMEOUT, MYF(0)); + return 1; + } + } + return 0; +} I think you can remove the above. +flush table t; +lock table t write; +ERROR 42S02: Unknown table 't' I think it is wrong that we get an err for the lock. We should fix it so that we open the table local GTT table and do not take a lock. (In other words, it should work as normal lock tables for tmp tables). @@ -5970,6 +5970,12 @@ my_bool open_global_temporary_table(THD *thd, TABLE_SHARE *source, { DBUG_ASSERT(!thd->rgi_slave); // slave won't use global temporary tables + if (thd->lex->sql_command == SQLCOM_LOCK_TABLES) + { + my_error(ER_BAD_TABLE_ERROR, MYF(0), source->table_name.str); + return TRUE; + } + See above. We should remove the above and instead open the table normally. Author: Nikita Malyavin <nikitamalyavin(a)gmail.com> Date: Tue Mar 11 02:08:10 2025 +0100 Replication support Please do not use 'show binlog events' as this will cause result conflicts with any changes in the binlog format and server changes. You have now things like Server ver: 11.8.0-MariaDB-debug-log, Binlog ver: 4 in the test output use instead source include/show_binlog_events.inc; One can also does not need to use ../.. to access main tests. Here is a diff for the test: +++ b/mysql-test/suite/binlog/t/global_temporary_table.test @@ -4,7 +4,7 @@ set @old_binlog_annotate_row_events= @@global.binlog_annotate_row_events; set global binlog_annotate_row_events= OFF; set session binlog_annotate_row_events= OFF; -source ../../main/global_temporary_table.test; +source main/global_temporary_table.test; +source include/show_binlog_events.inc; -show binlog events; set global binlog_annotate_row_events= @old_binlog_annotate_row_events; ----- +bool is_user_tmp_table(TMP_TABLE_SHARE *share) +{ + if (share->db_create_options & HA_OPTION_GLOBAL_TEMPORARY_TABLE) + return false; + return share->tmp_table == TRANSACTIONAL_TMP_TABLE || + share->tmp_table == NON_TRANSACTIONAL_TMP_TABLE; +} The normal way to test for temporary table is: share->tmp_table != NO_TMP_TABLE; see is_temporary_table() This should be safe also for the above function. Add () around the return functions, to get editors to indent it correctly by default. I think the above function needs some comments. Please explain how things are: if (share->db_create_options & HA_OPTION_GLOBAL_TEMPORARY_TABLE) is true, this is a GTT definition table and tmp_table would be NO_TMP_TABLE. If this is a local GTT tables, then (share->db_create_options & HA_OPTION_GLOBAL_TEMPORARY_TABLE) is false and share->from_share is true. It would be good if the above function would have good enough comments to explain all the above. We need to describe exactly how things are in some please in the source. Could you add the description how to detect GTT tables and local GTT tables and how they differ from normal temporary tables at the start of temporary_tables.cc Especially how share->db_create_options and share->tmp_table are set. If you add this function first in tempoary_table.cc, it may explain how things are: bool is_user_tmp_table(TMP_TABLE_SHARE *share) { if (share->db_create_options & HA_OPTION_GLOBAL_TEMPORARY_TABLE) { /* This is either a global temporary table (GTT) definition table or local GTT table created from the GTT definition. If (share->tmp_table != NO_TMP_TABLE) then this is local GTT table. In this case share->from_share is also set and points to the global GTT definition. */ return false; } /* Return true of the table is non GTT temporary table */ return (share->tmp_table != NO_TMP_TABLE) }

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