分析Mysql表讀寫、索引等操作的sql語句效率優化問題

阿新 • • 發佈：2020-01-09

上次我們說到mysql的一些sql查詢方面的優化，包括檢視explain執行計劃，分析索引等等。今天我們分享一些分析mysql表讀寫、索引等等操作的sql語句。

閒話不多說，直接上程式碼：

反映表的讀寫壓力

SELECT file_name AS file,count_read,sum_number_of_bytes_read AS total_read,count_write,sum_number_of_bytes_write AS total_written,(sum_number_of_bytes_read + sum_number_of_bytes_write) AS total
 FROM performance_schema.file_summary_by_instance
ORDER BY sum_number_of_bytes_read+ sum_number_of_bytes_write DESC;

反映檔案的延遲

SELECT (file_name) AS file,count_star AS total,CONCAT(ROUND(sum_timer_wait / 3600000000000000,2),'h') AS total_latency,CONCAT(ROUND(sum_timer_read / 1000000000000,'s') AS read_latency,CONCAT(ROUND(sum_timer_write / 3600000000000000,'h')AS write_latency
 FROM performance_schema.file_summary_by_instance
ORDER BY sum_timer_wait DESC;

table 的讀寫延遲

SELECT object_schema AS table_schema,object_name AS table_name,'h') as total_latency,CONCAT(ROUND((sum_timer_wait / count_star) / 1000000,'us') AS avg_latency,CONCAT(ROUND(max_timer_wait / 1000000000,'ms') AS max_latency
 FROM performance_schema.objects_summary_global_by_type
    ORDER BY sum_timer_wait DESC;

查看錶操作頻度

SELECT object_schema AS table_schema,count_star AS rows_io_total,count_read AS rows_read,count_write AS rows_write,count_fetch AS rows_fetchs,count_insert AS rows_inserts,count_update AS rows_updates,count_delete AS rows_deletes,CONCAT(ROUND(sum_timer_fetch / 3600000000000000,'h') AS fetch_latency,CONCAT(ROUND(sum_timer_insert / 3600000000000000,'h') AS insert_latency,CONCAT(ROUND(sum_timer_update / 3600000000000000,'h') AS update_latency,CONCAT(ROUND(sum_timer_delete / 3600000000000000,'h') AS delete_latency
   FROM performance_schema.table_io_waits_summary_by_table
    ORDER BY sum_timer_wait DESC ;

索引狀況

SELECT OBJECT_SCHEMA AS table_schema,OBJECT_NAME AS table_name,INDEX_NAME as index_name,COUNT_FETCH AS rows_fetched,CONCAT(ROUND(SUM_TIMER_FETCH / 3600000000000000,'h') AS select_latency,COUNT_INSERT AS rows_inserted,CONCAT(ROUND(SUM_TIMER_INSERT / 3600000000000000,COUNT_UPDATE AS rows_updated,CONCAT(ROUND(SUM_TIMER_UPDATE / 3600000000000000,COUNT_DELETE AS rows_deleted,CONCAT(ROUND(SUM_TIMER_DELETE / 3600000000000000,'h')AS delete_latency
FROM performance_schema.table_io_waits_summary_by_index_usage
WHERE index_name IS NOT NULL
ORDER BY sum_timer_wait DESC;

全表掃描情況

SELECT object_schema,object_name,count_read AS rows_full_scanned
 FROM performance_schema.table_io_waits_summary_by_index_usage
WHERE index_name IS NULL
  AND count_read > 0
ORDER BY count_read DESC;

沒有使用的index

SELECT object_schema,index_name
  FROM performance_schema.table_io_waits_summary_by_index_usage
 WHERE index_name IS NOT NULL
  AND count_star = 0
  AND object_schema not in ('mysql','v_monitor')
  AND index_name <> 'PRIMARY'
 ORDER BY object_schema,object_name;

糟糕的sql問題摘要

SELECT (DIGEST_TEXT) AS query,SCHEMA_NAME AS db,IF(SUM_NO_GOOD_INDEX_USED > 0 OR SUM_NO_INDEX_USED > 0,'*','') AS full_scan,COUNT_STAR AS exec_count,SUM_ERRORS AS err_count,SUM_WARNINGS AS warn_count,(SUM_TIMER_WAIT) AS total_latency,(MAX_TIMER_WAIT) AS max_latency,(AVG_TIMER_WAIT) AS avg_latency,(SUM_LOCK_TIME) AS lock_latency,format(SUM_ROWS_SENT,0) AS rows_sent,ROUND(IFNULL(SUM_ROWS_SENT / NULLIF(COUNT_STAR,0),0)) AS rows_sent_avg,SUM_ROWS_EXAMINED AS rows_examined,ROUND(IFNULL(SUM_ROWS_EXAMINED / NULLIF(COUNT_STAR,0)) AS rows_examined_avg,SUM_CREATED_TMP_TABLES AS tmp_tables,SUM_CREATED_TMP_DISK_TABLES AS tmp_disk_tables,SUM_SORT_ROWS AS rows_sorted,SUM_SORT_MERGE_PASSES AS sort_merge_passes,DIGEST AS digest,FIRST_SEEN AS first_seen,LAST_SEEN as last_seen
  FROM performance_schema.events_statements_summary_by_digest d
where d
ORDER BY SUM_TIMER_WAIT DESC
limit 20;

掌握這些sql，你能輕鬆知道你的庫那些表存在問題，然後考慮怎麼去優化。

總結

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