Direct SQL

Direct SQL is a way to map reduced execution on remote backends and store the results in a local table. This can either be sequential, using the UDF function spider_direct_sql, or concurrently, using spider_bg_direct_sql.

MariaDB starting with 10.0.4

The Spider storage engine was introduced in MariaDB 10.0.4, Direct SQL is reported to not work in the first releases. It is expected to be fixed in MariaDB 10.0.9. Ask a MariaDB Corporation representative for the available patch.

spider1 backend << EOF 
CREATE TEMPORARY TABLE res
(
  id int(10) unsigned NOT NULL,
  k int(10) unsigned NOT NULL DEFAULT '0',
  c char(120) NOT NULL DEFAULT '',
  pad char(60) NOT NULL DEFAULT ''
) ENGINE=MEMORY;
 
SELECT spider_direct_sql(
'SELECT * FROM sbtest s  WHERE s.id IN(10,12,13)',
  'res',   
  concat('host "', host, '", port "', port, '", user "', username, '", password "', password, '", database "', tgt_db_name, '"')
) a 
FROM 
  mysql.spider_tables 
WHERE 
  db_name = 'backend' and table_name like 'sbtest#P#pt%';

SELECT * FROM res; 
EOF

Or if you are using a SERVER:

SELECT spider_direct_sql( 
  'SELECT * FROM sbtest s  WHERE s.id IN(10,12,13)',
  'res',
  concat('server "', server, '"')
) a
  FROM mysql.spider_tables
  WHERE db_name = 'backend' and table_name like 'sbtest#P#pt%' ;

The default for spider_bg_direct_sql is to access concurrently all backends. If you have multiple partitions store inside a single backend, you still can increase parallelism affecting different channels to each partitions.

CREATE TEMPORARY TABLE res
(
  id int(10) unsigned NOT NULL , 
  col_microsec DATETIME(6) default NOW(8),
  db varchar(20)
) ENGINE=MEMORY;

SELECT spider_bg_direct_sql( 'SELECT count(*) ,min(NOW(6)),min(DATABASE())) FROM sbtest',   'res',  concat('srv "', server,'" cch ',@rn:=@rn+1  ) ) a  FROM    mysql.spider_tables,(SELECT @rn:=1) t2  WHERE    db_name = 'bsbackend' and table_name like 'sbtest#P#pt%';

Direct Handler Socket

Check that Handler Socket is running on the backend nodes

:~# backend2 -e "show variables like 'handler%'"
+-------------------------------+---------------+
| Variable_name                 | Value         |
+-------------------------------+---------------+
| handlersocket_accept_balance  | 0             |
| handlersocket_address         | 192.168.0.201 |
| handlersocket_backlog         | 32768         |
| handlersocket_epoll           | 1             |
| handlersocket_plain_secret    |               |
| handlersocket_plain_secret_wr |               |
| handlersocket_port            | 20500         |
| handlersocket_port_wr         | 20501         |
| handlersocket_rcvbuf          | 0             |
| handlersocket_readsize        | 0             |
| handlersocket_sndbuf          | 0             |
| handlersocket_threads         | 4            |
| handlersocket_threads_wr      | 1             |
| handlersocket_timeout         | 300           |
| handlersocket_verbose         | 10            |
| handlersocket_wrlock_timeout  | 12            |
+-------------------------------+---------------+
spider1 backend << EOF 
CREATE TEMPORARY TABLE res
(
  id int(10) unsigned NOT NULL,
  k int(10) unsigned NOT NULL DEFAULT '0',
  c char(120) NOT NULL DEFAULT '',
  pad char(60) NOT NULL DEFAULT ''
) ENGINE=MEMORY;
 
SELECT spider_direct_sql('1\t=\t1\t2\t100000\t0','res', 'host "192.168.0.202", table "sbtest", database "test", port "20500", access_mode "1"');

Inter Nodes Copy Table

The UDF function spider_copy_tables is available for copying table data from the source link ID to the destination link ID list without stopping your service for copying

spider_copy_tables(Spider table name, source link ID, destination link ID list[, parameters])

  • Returns 1 if copying data succeeded.
  • Returns 0 if copying data failed.

If the Spider table is partitioned, you must set "Spider table name" with a part name such as "table_name#P#part_name".

You can check the table name and the link ID with the part name using the following SQL:

SELECT table_name FROM mysql.spider_tables;

Resharding

General Log

To capture all queries sent to remote backends on a Spider Node :

SET GLOBAL general_log=ON; 
SET GLOBAL spider_general_log=ON;
SET GLOBAL spider_log_result_errors=1;
SET GLOBAL spider_log_result_error_with_sql=3;

Compiling in Debug Mode

Compile MariaDB in debug mode

#cmake -DBUILD_CONFIG=mysql_release -DCMAKE_BUILD_TYPE=Debug  -DWITH_FAST_MUTEXES=ON  -DWITH_VALGRIND=ON

Run MariaDB the following way to have a detailed command trace file

mysqld --debug=S:T:t:r:p:n:L:i:F:f:D:d,info,error,query,qcache,my,exit,general,where:O,/tmp/mysqld.trace 

Or with Valgrind to get a complete stack trace on a crash.

valgrind /usr/local/mysql/bin/mysqld --basedir=/usr/local/mysql --datadir=/data/inetbase/mysql --plugin-dir=/usr/local/mysql/lib/plugin --user=mysql --log-error=/data/inetbase/mysql/lucifer.err --open-files-limit=65000 --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/run/mysqld/mysqld.sock --port=3306

Report the issue in MariaDB JIRA (see Reporting Bugs) or to the MariaDB Corporation support center.

Compiling in Static

Available since version 3.1.14

To activate spider as a static plugin change "MODULE_ONLY" to "MANDATORY" in storage/spider/CMakeList.txt before compiling

Note that Spider UDF functions will not work with such settings.

Status Variables

A number of new status variables have been introduced:

Information Schema Tables

+-------------------+---------------------+------+-----+---------+-------+
| Field             | Type                | Null | Key | Default | Extra |
+-------------------+---------------------+------+-----+---------+-------+
| ID                | int(10) unsigned    | NO   |     | 0       |       |
| FUNC_NAME         | varchar(64)         | YES  |     | NULL    |       |
| FILE_NAME         | varchar(64)         | YES  |     | NULL    |       |
| LINE_NO           | int(10) unsigned    | YES  |     | NULL    |       |
| TOTAL_ALLOC_MEM   | bigint(20) unsigned | YES  |     | NULL    |       |
| CURRENT_ALLOC_MEM | bigint(20)          | YES  |     | NULL    |       |
| ALLOC_MEM_COUNT   | bigint(20) unsigned | YES  |     | NULL    |       |
| FREE_MEM_COUNT    | bigint(20) unsigned | YES  |     | NULL    |       |
+-------------------+---------------------+------+-----+---------+-------+

Performance Schema

The Performance schema is commonly used to troubleshoot issues that consume time inside your workload. The Performance schema should not be activated for servers that are experimenting constant heavy load, but most of time it is acceptable to lose 5% to 20% additional CPU to keep track of server internals execution.

To activate the performance schema, use the performance_schema system variable and add the following to the server section of the MariaDB configuration file.

performance_schema=on

Activate the Spider probes to be monitored.

UPDATE performance_schema.setup_instruments SET ENABLED='YES', TIMED='yes' WHERE NAME LIKE '%spider%';

Run your queries ...

And check the performance metrics. Remove specific Spider metrics to have a more global view.

SELECT * FROM performance_schema.events_waits_summary_global_by_event_name WHERE COUNT_STAR<>0 AND EVENT_NAME LIKE '%spider%' ORDER BY SUM_TIMER_WAIT DESC LIMIT 10;

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