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In MySQL 8.0.26, incompatible【ˌɪnkəmˈpætəbl 不相容的，不兼容的，互斥的;The thread is doing a first phase to find all matching rows before updating them. This has to be done if the UPDATE is changing the index that is used to find the involved【ɪnˈvɑːlvd 参与;(评判或作决定的)准则;

To ascertain【ˌæsərˈteɪn 查明;弄清;】 what your MySQL server is doing, it can be helpful to examine【ɪɡˈzæmɪn 检查;审查;(仔细地)检验;调查;考察;考查;测验(某人);（尤指在法庭上）审问，查问;

Benchmark your application and database to find out where the bottlenecks are. After fixing one bottleneck (or by replacing it with a “dummy” module), you can proceed to identify the next bottleneck. Even if the overall【ˌoʊvərˈɔːl , ˈoʊvərɔːl 总体的;

第一部分 Buffering and CachingMySQL uses several strategies that cache information in memory buffers to increase performance.1InnoDB Buffer Pool OptimizationInnoDB maintains a storage area called the buffer pool for caching data and indexes in memory. K

the thread that executes a statement to the named resource group temporarily (for the duration of the statement). It requires the RESOURCE_GROUP_ADMIN or RESOURCE_GROUP_USER privilege.QB_NAME hints can be used to make explicit【ɪkˈsplɪsɪt 明确的;

Subquery hints affect whether to use semijoin transformations and which semijoin strategies to permit, and, when semijoins are not used, whether to use subquery materialization or IN-to-EXISTS transformations【ˌtrænsfərˈmeɪʃənz (彻底的)变化，改观，转变，改革;(用于南非)民主改革;

The server maintains histogram【ˈhɪstəɡræm 直方图;（统计学的）直方图，矩形图;

书接上回Rematerialize (X,...) is displayed in the EXPLAIN row for table T, where X is any lateral【ˈlætərəl 横向的;侧面的;向侧面移动的;

Depending on the details of your tables, columns, indexes, and the conditions in your WHERE clause, the MySQL optimizer considers many techniques to efficiently perform the lookups involved in an SQL query. A query on a huge【hjuːdʒ 巨大的;非常成功的;极多的;走红的;程度高的;

InnoDB is the storage engine that MySQL customers typically use in production databases where reliability【rɪˌlaɪə'bɪləti 可靠性;】 and concurrency【并发;

推行，采用(规章制度);

indexes: DESC in an index definition is no longer ignored but causes storage of key values in descending order. Previously, indexes could be scanned in reverse order but at a performance penalty【ˈpenəlti 处罚;】. UTC values that are distinct【dɪˈstɪŋkt 不同的;

Although it can be tempting【ˈtemptɪŋ 诱人的;吸引人的;有吸引力的;

（尤指飞机的）顶舱;生命统计的，生死统计的;生气勃勃的，充满生机的;致命的，生死攸关的;大致的，大概的（方向或地区）;Querying statistics columns does not store or update statistics in the mysql.index_stats and mysql.table_stats dictionary tables under these circumstances【ˈsɜrkəmˌstænsəz , ˈsɜrkəmˌstænsɪz 环境;

(指认为可做夫妻的男女)合意的，合适的，中意的;• For a query in which the condition is on the tables of a view created using ALGORITHM=TEMPTABLE instead of on the view itself, the multiple equality is not recognized at resolution【ˌrezəˈluːʃn 决议;(问题、分歧等的)解决，消除;(工作等的)分派，布置;

The MySQL query optimizer has different strategies available to evaluate【ɪˈvæljueɪt 评价;评估;估计;• Materialization【实现；具体化；物质化;

18 DISTINCT OptimizationDISTINCT combined with ORDER BY needs a temporary table in many cases.Because DISTINCT may use GROUP BY, learn how MySQL works with columns in ORDER BY or HAVING clauses that are not part of the selected columns.In most cases,

• In this query, key_part1 is constant, so all rows accessed through the index are in key_part2 order, and an index on (key_part1, key_part2) avoids sorting if the WHERE clause is selective【sɪˈlektɪv 选择性的;• The query uses ORDER BY on nonconsecutive【不相邻的;

(食物的)一份，一客;】 rows are those rows passed from one table in a join to the next. In general, the optimizer attempts to put tables with low prefix counts early in the join order to keep the number of row combinations from increasing rapidly【'ræpɪdli 迅速;

The syntax of table_factor is extended in comparison with the SQL Standard. The latter accepts only table_reference, not a list of them inside a pair of parentheses. This is a conservative【kənˈsɜːrvətɪv 保守的;(恒星、行星等的)合;• It is a disjunction【dɪsˈdʒʌŋkʃn 分离;

their results into one. This access method merges index scans from a single table only, not scans across multiple tables. The merge can produce unions, intersections, or unions-of-intersections of its underlying scans.The criteria【kraɪ'tɪriə 标准;

• Isolate and tune any part of the query, such as a function call, that takes excessive【ɪkˈsesɪv 过度的;过分的;

Optimization involves【ɪnˈvɑːlvz 需要;影响;(使)参加，加入;包含;牵涉;牵连;使成为必然部分(或结果);

whereas in its own binary log, the transaction’s immediate_commit_timestamp corresponds to when the replica committed the transaction. immediate--【ɪˈmiːdiət 当前的;Source and target tables for replication do not have to be identical【aɪˈdentɪkl 完全相同的;

In addition to the built-in asynchronous replication, MySQL 8.0 supports an interface to semisynchronous replication that is implemented by plugins. This section discusses what semisynchronous replication is and how it works. The following sections cover t

You can tell a replica to change to a new source using the CHANGE REPLICATION SOURCE TO statement (prior to MySQL 8.0.23: CHANGE MASTER TO. The replica does not check whether the databases on the source are compatible【kəmˈpætəbl 兼容的，可共存的;合得来的，意气相投的;

The SHOW REPLICA STATUS statement, which you must execute on each replica, provides information about the configuration and status of the connection between the replica server and the source server. From MySQL 8.0.22, SHOW SLAVE STATUS is deprecated, and S

律>有相等权力的，同时(实施)的;执著地做】 even if the replicated transaction is not written to the binary log on the replica, or is filtered out on the replica. The MySQL system table mysql.gtid_executed is used to preserve【prɪˈzɜːrv 保存;偏向一方的，偏袒的，不公平的;5.注意scheduled events。

• SELECT ... FOR UPDATE and SELECT ... FOR SHARE statements that use a unique index acquire locks for scanned rows, and release the locks for rows that do not qualify for inclusion【ɪnˈkluːʒn (被)包括，包含;被包括的人(或事物);(评判或作决定的)准则;(个人或集体)专用的，专有的，独有的，独占的;

The InnoDB transaction model aims to combine the best properties【ˈprɑpərtiz 财产;特性;房地产;不动产;财物;庄园;所有物;房屋及院落;

For example, if the id column has a unique index, the following statement uses only an index-record lock for the row having id value 100 and it does not matter whether other sessions insert rows in the preceding【prɪˈsiːdɪŋ 在前的;】, where a round【raʊnd 圆形的;

使(别人)接受自己的意见;

(与系列规则相)符合的，一致的;】 of the column length are truncated prior to insertion and a warning is generated, regardless of the SQL mode in use. For CHAR columns, truncation of excess trailing spaces from inserted values is performed silently【ˈsaɪləntli 默默地;

numeric data types (INTEGER, SMALLINT, DECIMAL, and NUMERIC), as well as the approximate【əˈprɑːksɪmeɪt 近似的;that is, the number of digits following the decimal【ˈdesɪml 小数的;】. The precision represents the number of significant【sɪɡˈnɪfɪkənt 重要的, 有重大意义的;

偏向一方的，偏袒的，不公平的;The MySQL server has a compiled-in default character set and collation. To change these defaults, use the --character-set-server and --collation-server options when you start the server.The collation must be a legal【ˈliːɡl 合法的;显著的, 值得注意的;

• They are sufficient【səˈfɪʃnt 足够的;(理由、条件)充足的, 充分的;充足的;<古>有充分能力的, 足以胜任的;Supplementary【ˌsʌplɪˈmentri 补充的;额外的;补充性的;外加的;增补性的;

, it is necessary to understand that when the client tells the server which character set it wants to use, it really tells the server the default collation for that character set. Therefore, the aforementioned【əˈfɔːrmenʃənd 上述的;Several【ˈsevrəl 不同的，各种各样的;

MySQL includes character【ˈkærəktər 字母，符号;】 set support that enables you to store data using a variety【vəˈraɪəti (同一事物的)不同种类，多种式样;变化;(植物、语言等的)变种，变体;多样化;综艺节目;品种;多变性;异体;】 of character sets and perform comparisons【kəmˈpɛrəsənz 比较;对比;相比;

使成为必然部分(或结果);When you insert any other value into an AUTO_INCREMENT column, the column is set to that value and the sequence is reset so that the next automatically generated value follows sequentially from the largest column value.--如果自增列指明的插入值，以插入值为准。

(尤指像小孩一样)可笑的，荒唐的，冒傻气的;(事情发生的)背景，环境，来龙去脉;Finding animals with birthdays in the upcoming month is also simple. Suppose that the current month is April. Then the month value is 4 and you can look for animals born in May (month 5) like this: --计算下个月，过生日的；