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4.2.4 Server Status Variables - MySQL

If you need to administer MySQL, this article gets you off to a good start. In this section, we discuss system and other variables, then begin to look at general security issues. The second of a multi-part series, it is excerpted from chapter four of the book MySQL Administrator's Guide, written by Paul Dubois (Sams; ISBN: 0672326345).

TABLE OF CONTENTS:
  1. Security and More in MySQL Databases
  2. 4.2.3.1.2 Dynamic System Variables
  3. 4.2.4 Server Status Variables
  4. 4.3 General Security Issues
  5. 4.3.2 Making MySQL Secure Against Attackers
  6. 4.3.4 Security Issues with LOAD DATA LOCAL
By: Sams Publishing
Rating: starstarstarstarstar / 3
June 01, 2006

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The server maintains many status variables that provide information about its operations. You can view these variables and their values by using the SHOW STATUS statement:

mysql> SHOW STATUS;
+--------------------------+------------+
| Variable_name            | Value      |
+--------------------------+------------+
| Aborted_clients          | 0          |
| Aborted_connects         | 0          |
| Bytes_received           | 155372598  |
| Bytes_sent               | 1176560426 |
| Connections              | 30023      |
| Created_tmp_disk_tables  | 0          |
| Created_tmp_files        | 60         |
| Created_tmp_tables       | 8340       |
| Delayed_errors           | 0          |
| Delayed_insert_threads   | 0          |
| Delayed_writes           | 0          |
| Flush_commands           | 1          |
| Handler_delete           | 462604     |
| Handler_read_first       | 105881     |
| Handler_read_key         | 27820558   |
| Handler_read_next        | 390681754  |
| Handler_read_prev        | 6022500    |
| Handler_read_rnd         | 30546748   |
| Handler_read_rnd_next    | 246216530  |
| Handler_update           | 16945404   |
| Handler_write            | 60356676   |
| Key_blocks_used          | 14955      |
| Key_read_requests        | 96854827   |
| Key_reads                | 162040     |
| Key_write_requests       | 7589728    |
| Key_writes               | 3813196    |
| Max_used_connections     | 0          |
| Not_flushed_delayed_rows | 0          |
| Not_flushed_key_blocks   | 0          |
| Open_files               | 2          |
| Open_streams             | 0          |
| Open_tables              | 1          |
| Opened_tables            | 44600      |
| Qcache_free_blocks       | 36         |
| Qcache_free_memory       | 138488     |
| Qcache_hits              | 79570      |
| Qcache_inserts           | 27087      |
| Qcache_lowmem_prunes     | 3114       |
| Qcache_not_cached        | 22989      |
| Qcache_queries_in_cache  | 415        |
| Qcache_total_blocks      | 912        |
| Questions                | 2026873    |
| Select_full_join         | 0          |
| Select_full_range_join   | 0          |
| Select_range             | 99646      |
| Select_range_check       | 0          |
| Select_scan              | 30802      |
| Slave_open_temp_tables   | 0          |
| Slave_running            | OFF        |
| Slow_launch_threads      | 0          |
| Slow_queries             | 0          |
| Sort_merge_passes        | 30         |
| Sort_range               | 500        |
| Sort_rows                | 30296250   |
| Sort_scan                | 4650       |
| Table_locks_immediate    | 1920382    |
| Table_locks_waited       | 0          |
| Threads_cached           | 0          |
| Threads_connected        | 1          |
| Threads_created          | 30022      |
| Threads_running          | 1          |
| Uptime                   | 80380      |
+--------------------------+------------+

Many status variables are reset to 0 by the FLUSH STATUS statement.

The status variables have the following meanings. The Com_xxx statement counter variables were added beginning with MySQL 3.23.47. The Qcache_xxx query cache variables were added beginning with MySQL 4.0.1. Otherwise, variables with no version indicated have been present since at least MySQL 3.22.

  • Aborted_clients

    The number of connections that were aborted because the client died without closing the connection properly. See Section A.2.10, "Communication Errors and Aborted Connections."

  • Aborted_connects

    The number of tries to connect to the MySQL server that failed. See Section A.2.10, "Communication Errors and Aborted Connections."

  • Binlog_cache_use

    The number of transactions that used the temporary binary log cache. This variable was added in MySQL 4.1.2.

  • Binlog_cache_disk_use

    The number of transactions that used the temporary binary log cache but that exceeded the value of binlog_cache_size and used a temporary file to store statements from the transaction. This variable was added in MySQL 4.1.2.

  • Bytes_received

    The number of bytes received from all clients. This variable was added in MySQL 3.23.7.

  • Bytes_sent

    The number of bytes sent to all clients. This variable was added in MySQL 3.23.7.

  • Com_xxx

    The number of times each xxx statement has been executed. There is one status variable for each type of statement. For example, Com_delete and Com_insert count DELETE and INSERT statements.

  • Connections

    The number of connection attempts (successful or not) to the MySQL server.

  • Created_tmp_disk_tables

    The number of temporary tables on disk created automatically by the server while executing statements. This variable was added in MySQL 3.23.24.

  • Created_tmp_files

    How many temporary files mysqld has created. This variable was added in MySQL 3.23.28.

  • Created_tmp_tables

    The number of in-memory temporary tables created automatically by the server while executing statements. If Created_tmp_disk_tables is big, you may want to increase the tmp_table_size value to cause temporary tables to be memory-based instead of disk-based.

  • Delayed_errors

    The number of rows written with INSERT DELAYED for which some error occurred (probably duplicate key).

  • Delayed_insert_threads

    The number of INSERT DELAYED handler threads in use.

  • Delayed_writes

    The number of INSERT DELAYED rows written.

  • Flush_commands

    The number of executed FLUSH statements.

  • Handler_commit

    The number of internal COMMIT statements. This variable was added in MySQL 4.0.2.

  • Handler_delete

    The number of times a row was deleted from a table.

  • Handler_read_first

    The number of times the first entry was read from an index. If this is high, it suggests that the server is doing a lot of full index scans; for example, SELECT col1 FROM foo, assuming that col1 is indexed.

  • Handler_read_key

    The number of requests to read a row based on a key. If this is high, it is a good indication that your queries and tables are properly indexed.

  • Handler_read_next

    The number of requests to read the next row in key order. This will be incremented if you are querying an index column with a range constraint or if you are doing an index scan.

  • Handler_read_prev

    The number of requests to read the previous row in key order. This read method is mainly used to optimize ORDER BY ... DESC. This variable was added in MySQL 3.23.6.

  • Handler_read_rnd

    The number of requests to read a row based on a fixed position. This will be high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan whole tables or you have joins that don't use keys properly.

  • Handler_read_rnd_next

    The number of requests to read the next row in the data file. This will be high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.

  • Handler_rollback

    The number of internal ROLLBACK statements. This variable was added in MySQL 4.0.2.

  • Handler_update

    The number of requests to update a row in a table.

  • Handler_write

    The number of requests to insert a row in a table.

  • Key_blocks_used

    The number of used blocks in the key cache. You can use this value to determine how much of the key cache is in use; see the discussion of key_buffer_size in Section 4.2.3, "Server System Variables."

  • Key_read_requests

    The number of requests to read a key block from the cache.

  • Key_reads

    The number of physical reads of a key block from disk. If Key_reads is big, then your key_buffer_size value is probably too small. The cache miss rate can be calculated as Key_reads/Key_read_requests.

  • Key_write_requests

    The number of requests to write a key block to the cache.

  • Key_writes

    The number of physical writes of a key block to disk.

  • Max_used_connections

    The maximum number of connections that have been in use simultaneously since the server started.

  • Not_flushed_delayed_rows

    The number of rows waiting to be written in INSERT DELAY queues.

  • Not_flushed_key_blocks

    The number of key blocks in the key cache that have changed but haven't yet been flushed to disk.

  • Open_files

    The number of files that are open.

  • Open_streams

    The number of streams that are open (used mainly for logging).

  • Open_tables

    The number of tables that are open.

  • Opened_tables

    The number of tables that have been opened. If Opened_tables is big, your table_cache value is probably too small.

  • Qcache_free_blocks

    The number of free memory blocks in query cache.

  • Qcache_free_memory

    The amount of free memory for query cache.

  • Qcache_hits

    The number of cache hits.

  • Qcache_inserts

    The number of queries added to the cache.

  • Qcache_lowmem_prunes

    The number of queries that were deleted from the cache because of low memory.

  • Qcache_not_cached

    The number of non-cached queries (not cachable, or due to query_cache_type).

  • Qcache_queries_in_cache

    The number of queries registered in the cache.

  • Qcache_total_blocks

    The total number of blocks in the query cache.

  • Questions

    The number of queries that have been sent to the server.

  • Rpl_status

    The status of failsafe replication (not yet implemented).

  • Select_full_join

    The number of joins that do not use indexes. If this value is not 0, you should carefully check the indexes of your tables. This variable was added in MySQL 3.23.25.

  • Select_full_range_join

    The number of joins that used a range search on a reference table. This variable was added in MySQL 3.23.25.

  • Select_range

    The number of joins that used ranges on the first table. (It's normally not critical even if this is big.) This variable was added in MySQL 3.23.25.

  • Select_range_check

    The number of joins without keys that check for key usage after each row. (If this is not 0, you should carefully check the indexes of your tables.) This variable was added in MySQL 3.23.25.

  • Select_scan

    The number of joins that did a full scan of the first table. This variable was added in MySQL 3.23.25.

  • Slave_open_temp_tables

    The number of temporary tables currently open by the slave SQL thread. This variable was added in MySQL 3.23.29.

  • Slave_running

    This is ON if the server is a slave that is connected to a master. This variable was added in MySQL 3.23.16.

  • Slow_launch_threads

    The number of threads that have taken more than slow_launch_time seconds to create. This variable was added in MySQL 3.23.15.

  • Slow_queries

    The number of queries that have taken more than long_query_time seconds. See Section 4.8.5, "The Slow Query Log."

  • Sort_merge_passes

    The number of merge passes the sort algorithm has had to do. If this value is large, you should consider increasing the value of the sort_buffer_size system variable. This variable was added in MySQL 3.23.28.

  • Sort_range

    The number of sorts that were done with ranges. This variable was added in MySQL 3.23.25.

  • Sort_rows

    The number of sorted rows. This variable was added in MySQL 3.23.25.

  • Sort_scan

    The number of sorts that were done by scanning the table. This variable was added in MySQL 3.23.25.

  • Ssl_xxx

    Variables used for SSL connections. These variables were added in MySQL 4.0.0.

  • Table_locks_immediate

    The number of times that a table lock was acquired immediately. This variable was added as of MySQL 3.23.33.

  • Table_locks_waited

    The number of times that a table lock could not be acquired immediately and a wait was needed. If this is high, and you have performance problems, you should first optimize your queries, and then either split your table or tables or use replication. This variable was added as of MySQL 3.23.33.

  • Threads_cached

    The number of threads in the thread cache. This variable was added in MySQL 3.23.17.

  • Threads_connected

    The number of currently open connections.

  • Threads_created

    The number of threads created to handle connections. If Threads_created is big, you may want to increase the thread_cache_size value. The cache hit rate can be calculated as Threads_created/Connections. This variable was added in MySQL 3.23.31.

  • Threads_running

    The number of threads that are not sleeping.

  • Uptime

    The number of seconds the server has been up.



 
 
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