MySQL 8.0的新特性（二）

一、地理資訊系統 GIS

8.0 版本提供對地形的支援，其中包括了對空間參照系的資料源資訊的支援，SRS aware spatial資料類型，空間索引，空間函數。總而言之，8.0版本可以了解地球表面的經緯度資訊，而且可以在任意受支援的5000個空間參照系中計算地球上任意兩點之間的距離。

MySQL 8.0 delivers geography support. This includes meta-data support for Spatial Reference System (SRS), as well as SRS aware spatial datatypes, spatial indexes, and spatial functions. In short, MySQL 8.0 understands latitude and longitude coordinates on the earth’s surface and can, for example, correctly calculate the distances between two points on the earths surface in any of the about 5000 supported spatial reference systems.

• 空間參照系 Spatial Reference System (SRS)

ST_SPATIAL_REFERENCE_SYSTEMS 存在于information schema視圖庫中，提供了可供使用的SRS坐标系統的名稱。

每個SRS坐标系統都有一個SRID編号。8.0版本支援EPSG Geodetic Parameter Dataseset中的5千多個坐标系統（包括立體模和2D平面地球模型）

The ST_SPATIAL_REFERENCE_SYSTEMS information schema view provides information about available spatial reference systems for spatial data. This view is based on the SQL/MM (ISO/IEC 13249-3) standard.

Each spatial reference system is identified by an SRID number. MySQL 8.0 ships with about 5000 SRIDs from the EPSG Geodetic Parameter Dataset, covering georeferenced ellipsoids and 2d projections (i.e. all 2D spatial reference systems).

• SRID 地理資料類型 SRID aware spatial datatypes

空間類的資料類型可以直接從SRS坐标系統的定義中擷取，例如：使用SRID 4326定義進行建表： CREATE TABLE t1 (g GEOMETRY SRID 4326); 。

SRID是适用于地理類型的資料類型。隻有同一SRID的的資料才會被插入到行中。與目前SRID資料類型的資料嘗試插入時，會報錯。未定義SRID編号的表将可以接受所有SRID編号的資料。

Spatial datatypes can be attributed with the spatial reference system definition, for example with SRID 4326 like this: CREATE TABLE t1 (g GEOMETRY SRID 4326);

The SRID is here a SQL type modifier for the GEOMETRY datatype. Values inserted into a column with an SRID property must be in that SRID. Attempts to insert values with other SRIDs results in an exception condition being raised. Unmodified types, i.e., types with no SRID specification, will continue to accept all SRIDs, as before.

8.0版本增加了 INFORMATION_SCHEMA.ST_GEOMETRY_COLUMNS 視圖，可以顯示目前執行個體中所有地理資訊的資料行及其對應的SRS名稱，編号，地理類型名稱。

MySQL 8.0 adds

the INFORMATION_SCHEMA.ST_GEOMETRY_COLUMNS view as specified in SQL/MM Part 3, Sect. 19.2. This view will list all GEOMETRY columns in the MySQL instance and for each column it will list the standard SRS_NAME , SRS_ID , and GEOMETRY_TYPE_NAME.

• SRID 空間索引 SRID aware spatial indexes

在空間資料類型上可以建立空間索引，建立空間索引的列必須非空，例如： CREATE TABLE t1 (g GEOMETRY SRID 4326 NOT NULL, SPATIAL INDEX(g));

Spatial indexes can be created on spatial datatypes. Columns in spatial indexes must be declared NOT NULL. For example like this: CREATE TABLE t1 (g GEOMETRY SRID 4326 NOT NULL, SPATIAL INDEX(g));

建立空間索引的列必須具有SRID資料辨別以用于優化器使用，如果将空間索引建在沒有SRID資料辨別的列上，将輸出waring資訊。

Columns with a spatial index should have an SRID type modifier to allow the optimizer to use the index. If a spatial index is created on a column that doesn’t have an SRID type modifier, a warning is issued.

• SRID 空間函數

8.0 增加了諸如 ST_Distance() 和 ST_Length() 等用于判斷資料的參數是否在SRS中，并計算其空間上的距離。到目前為止，ST_Distance和其他的空間關系型函數諸如ST_Within,ST_Intersects,ST_Contains,ST_Crosses都支援地理計算。其運算邏輯與行為參見 SQL/MM Part 3 Spatial

MySQL 8.0 extends spatial functions such as ST_Distance() and ST_Length() to detect that its parameters are in a geographic (ellipsoidal) SRS and to compute the distance on the ellipsoid. So far, ST_Distance and spatial relations such as ST_Within, ST_Intersects, ST_Contains, ST_Crosses, etc. support geographic computations. The behavior of each ST function is as defined in SQL/MM Part 3 Spatial.

二、字元集 Character Sets

8.0版本預設使用UTF8MB4作為預設字元集。相比較5.7版本，SQL性能（諸如排序UTF8MB4字元串）得到了很大的提升。UTF8MB4類型在網頁編碼上正占據着舉足輕重的地位，将其設為預設資料類型後，将會給絕大多數的MySQL使用者帶來便利。

MySQL 8.0 makes UTF8MB4 the default character set. SQL performance – such as sorting UTF8MB4 strings – has been improved by a factor of 20 in 8.0 as compared to 5.7. UTF8MB4 is the dominating character encoding for the web, and this move will make life easier for the vast majority of MySQL users.

• 預設的字元集從latin1變為 utf8mb4 ,預設排序校對規則從 latin1_swedish_ci 變為utf8mb4_800_ci_ai。

The default character set has changed from latin1 to utf8mb4 and the default collation has changed from latin1_swedish_ci to utf8mb4_800_ci_ai.

• utf8mb4同樣也成為libmysql，服務端指令行工具,server層的預設編碼

The changes in defaults applies to libmysql and server command tools as well as the server itself.

• utf8mb4同樣也成為MySQL測試架構的預設編碼

The changes are also reflected in MTR tests, running with new default charset.

• 排序校對規則的權重與大小寫基于Unicode委員會16年公布的Unicode 9.0.0版本。

The collation weight and case mapping are based on Unicode 9.0.0 , announced by the Unicode committee on Jun 21, 2016.

• 在以往的MySQL版本中，latin1編碼中的21種語言的特殊大小寫和排序校對規則被引入了 utf8mb4 排序校對規則。例如：捷克語的排序校對規則變成了utf8mb4_cs_800_ai_ci。

The 21 language specific case insensitive collations available for latin1 (MySQL legacy) have been implemented forutf8mb4 collations, for example the Czech collation becomes utf8mb4_cs_800_ai_ci. See complete list in WL#9108 . See blog post by Xing Zhang here .

• 增加了對特殊語境和重音敏感的排序校對規則的支援。8.0版本支援 DUCET (Default Unicode Collation Entry Table)全部三級排序校對規則。

Added support for case and accent sensitive collations. MySQL 8.0 supports all 3 levels of collation weight defined by DUCET (Default Unicode Collation Entry Table). See blog post by Xing Zhang here.

• utf8mb4 的 utf8mb4_ja_0900_as_cs 排序校驗規則對日語字元支援三級權重的排序。

Japanese utf8mb4_ja_0900_as_cs collation for utf8mb4 which sorts characters by using three levels’ weight. This gives the correct sorting order for Japanese. See blog post by Xing Zhang here.

• 對日語有額外的假名支援特性， utf8mb4_ja_0900_as_cs_ks中的ks表示假名區分。

Japanese with additional kana sensitive feature, utf8mb4_ja_0900_as_cs_ks, where ‘ks’ stands for ‘kana sensitive’. See blog post by Xing Zhang here.

• 把 Unicode 9.0.0之前所有排序校驗規則中的不填補變成填補字元，此舉有利于提升字元串的一緻性和性能。例如把字元串末尾的空格按照其他字元對待。之前的排序校驗規則在處理這種情況時保留字元串原樣。

Changed all new collations, from Unicode 9.0.0 forward, to be NO PAD instead of PAD STRING, ie., treat spaces at the end of a string like any other character. This is done to improve consistency and performance. Older collations are left in place.

See also blog posts by Bernt Marius Johnsen here, here and here.

三、資料類型 Datatypes

• 二進制資料類型的Bit-wise操作

8.0版本擴充了 bit-wise操作（如bit-wise AND等）的使用範圍，使得其在所有 BINARY 資料類型上都适用。在此之前隻支援整型資料，若強行在二進制資料類型上使用Bit-wise操作，将會隐式轉換為64位的BITINT類型，并可能丢失若幹位的資料。

從8.0版本之後，bit-wise操作可以在 BINARY 和BLOB類型上使用，且不用擔心精确度下降的問題。

MySQL 8.0 extends the bit-wise operations (‘bit-wise AND’, etc) to also work with [VAR]BINARY/[TINY|MEDIUM|LONG]BLOB. Prior to 8.0 bit-wise operations were only supported for integers. If you used bit-wise operations on binaries the arguments were implicitly cast to BIGINT (64 bit) before the operation, thus possibly losing bits.

From 8.0 and onward bit-wise operations work for all BINARY and BLOB data types, casting arguments such that bits are not lost.

• IPV6操作

8.0版本通過支援 BINARY 上的Bit-wise操作提升了IPv6資料的可操作性。5.6版本中引入了支援IPv6位址和16位二進制資料的互相轉換的INET6_ATON() 和 INET6_NTOA() 函數。

但是直到8.0之前，由于上一段中的問題我們都無法講IPv6轉換函數和bit-wise操作結合起來。由于 INET6_ATON() 可以正确的傳回128bit的VARBINARY(16)，如果我們想要将一個IPv6位址與網關位址進行比對，現在就可以使用 INET6_ATON(address)& INET6_ATON(network) 操作。

MySQL 8.0 improves the usability of IPv6 manipulation supporting bit-wise operations on BINARY data types. In MySQL 5.6 we introduced the INET6_ATON() and INET6_NTOA() functions which convert IPv6 addresses between text form like 'fe80::226:b9ff:fe77:eb17' and VARBINARY(16).

However, until now we could not combine these IPv6 functions with bit-wise operations since such operations would – wrongly – convert output to BIGINT. For example, if we have an IPv6 address and want to test it against a network mask, we can now use INET6_ATON(address)& INET6_ATON(network) because INET6_ATON() correctly returns the VARBINARY(16)datatype (128 bits). See blog post by Catalin Besleaga here.

• UUID 操作

8.0版本通過增加了三個新的函數（UUID_TO_BIN(), BIN_TO_UUID(), 和 IS_UUID()）提升了UUID的可用性。UUID_TO_BIN()可以将UUID格式的文本轉換成VARBINARY(16), BIN_TO_UUID()則與之相反， IS_UUID()用來校驗UUID的有效性。将UUID以 VARBINARY(16) 的方式存儲後，就可以使用實用的索引了。

UUID_TO_BIN() 函數可以原本轉換後的二進制數值中的時間相關位（UUID生成時有時間關聯）移到資料的開頭，這樣對索引來說更加友好而且可以減少在B樹中的随機插入，進而減少了插入耗時。

MySQL 8.0 improves the usability of UUID manipulations by implementing three new SQL functions: UUID_TO_BIN(), BIN_TO_UUID(), and IS_UUID(). The first one converts from UUID formatted text to VARBINARY(16), the second one from VARBINARY(16) to UUID formatted text, and the last one checks the validity of an UUID formatted text. The UUID stored as a VARBINARY(16) can be indexed using functional indexes.

The functions UUID_TO_BIN() and UUID_TO_BIN() can also shuffle the time-related bits and move them at the beginning making it index friendly and avoiding the random inserts in the B-tree, this way reducing the insert time. The lack of such functionality has been mentioned as one of the drawbacks of using UUID’s. See blog post by Catalin Besleaga here.

四、消耗敏感的模型

• 查詢優化器将會照顧到資料緩沖的狀況

8.0版本自動地根據資料是否存在于記憶體中而選擇查詢計劃，在以往的版本中，消耗敏感的模型始終假設資料在磁盤上。

正因為現在查詢記憶體資料和查詢硬碟資料的消耗常數不同，是以優化器會根據資料的位置選擇更加優化的讀取資料方式。

MySQL 8.0 chooses query plans based on knowledge about whether data resides in-memory or on-disk. This happens automatically, as seen from the end user there is no configuration involved. Historically, the MySQL cost model has assumed data to reside on spinning disks.

The cost constants associated with looking up data in-memory and on-disk are now different, thus, the optimizer will choose more optimal access methods for the two cases, based on knowledge of the location of data. See blog post by Øystein Grøvlen here.

• 查詢優化器的直方圖

8.0版本加入了直方圖統計資料。使用者可以根據直方圖針對表中的某列（一般為非索引列）生成資料分布統計資訊，這樣優化器就可以利用這些資訊去尋覓更加優化的查詢計劃。

直方圖最常見的使用場景就是計算字段的選擇性。

MySQL 8.0 implements histogram statistics. With Histograms, the user can create statistics on the data distribution for a column in a table, typically done for non-indexed columns, which then will be used by the query optimizer in finding the optimal query plan.

The primary use case for histogram statistics is for calculating the selectivity (filter effect) of predicates of the form “COLUMN operator CONSTANT”.

用以建立直方圖的 ANALYZE TABLE 文法現已被擴充了兩個新子句： UPDATE HISTOGRAM ON column [, column] [WITH n BUCKETS]和DROP HISTOGRAM ON column [, column]。

直方圖的總計總數（桶）是可以選的，預設100。直方圖的統計資訊被存儲在詞典表column_statistics中，并可以使用

information_schema.COLUMN_STATISTICS進行檢視。由于JSON資料格式的靈活性，直方圖現在以JSON對象存儲。

根據表的大小，ANALYZE TABLE指令會自動的判斷是否要表進行采樣，甚至會根據表中資料的分布情況和統計總量來決定建立等頻或者等高的直方圖。

The user creates a histogram by means of the ANALYZE TABLE syntax which has been extended to accept two new clauses: UPDATE HISTOGRAM ON column [, column] [WITH n BUCKETS] and DROP HISTOGRAM ON column [, column].

The number of buckets is optional, the default is 100. The histogram statistics are stored in the dictionary table “column_statistics” and accessible through the view information_schema.COLUMN_STATISTICS. The histogram is stored as a JSON object due to the flexibility of the JSON datatype.

ANALYZE TABLE will automatically decide whether to sample the base table or not, based on table size. It will also decide whether to build a singleton or a equi-height histogram based on the data distribution and the number of buckets specified. See blog post by Erik Frøseth here.

五、正規表達式 

與UTF8MB4的正則支援一同，8.0版本也增加了諸如 REGEXP_INSTR(), REGEXP_LIKE(), REGEXP_REPLACE(), 和REGEXP_SUBSTR()等新函數。

另外，系統中還增加了用以控制正規表達式緻性的 regexp_stack_limit (預設8000000比特) 和 regexp_time_limit (預設32步) 參數。REGEXP_REPLACE()也是社群中受呼聲比較高的特性。

MySQL 8.0 supports regular expressions for UTF8MB4 as well as new functions like REGEXP_INSTR(), REGEXP_LIKE(), REGEXP_REPLACE(), and REGEXP_SUBSTR().

The system variables regexp_stack_limit (default 8000000 bytes) and regexp_time_limit (default 32 steps) have been added to control the execution. The REGEXP_REPLACE() function is one of the most requested features by the MySQL community, for example see feature request reported as BUG #27389 by Hans Ginzel. See also blog posts by Martin Hansson here and Bernt Marius Johnsen here.

六、運維自動化特性

開發向的運維關心資料庫執行個體的可操作型，通常即可靠性，可用性，性能，安全，可觀測性，可管理性。關于InnoDB Cluster和MGR的可靠性我們将會另起新篇單獨介紹，接下來的段落将會介紹關于8.0版本針對表在其他可操作性上的改變。

Dev Ops care about operational aspects of the database, typically about reliability, availability, performance, security, observability, and manageability. High Availability comes with MySQL InnoDB Cluster and MySQL Group Replication which will be covered by a separate blog post. Here follows what 8.0 brings to the table in the other categories.

七、可靠性

8.0版本在整體上 增加了可靠性，原因如下：

MySQL 8.0 increases the overall reliability of MySQL because :

1、8.0版本将元資訊存儲與久經考驗的事務性存儲引擎InnoDB中。諸如使用者權限表，資料字典表，現在都使用 InnoDB進行存儲。

MySQL 8.0 stores its meta-data into InnoDB, a proven transactional storage engine. System tables such as Users and Privileges as well as Data Dictionary tables now reside in InnoDB.

2、8.0版本消除了會導緻非一緻性的一處隐患。在5.7及以前的版本中，存在着服務層和引擎層兩份資料字典，因而可能導緻在故障情況下的資料字典間的同步失敗。在8.0版本中，隻有一份資料字典。

MySQL 8.0 eliminates one source of potential inconsistency. In 5.7 and earlier versions there are essentially two data dictionaries, one for the Server layer and one for the InnoDB layer, and these can get out of sync in some crashing scenarios. In 8.0 there is only one data dictionary.

3、8.0版本實作了原子化，無懼當機的DDL。根據這個特性，DDL語句要麼被全部執行，要麼全部未執行。對于複制環境來說這是至關重要的，否則會導緻主從之間因為表結構不一緻，資料漂移的情況。

MySQL 8.0 ensures atomic, crash safe DDL. With this the user is guaranteed that any DDL statement will either be executed fully or not at all. This is particularly important in a replicated environment, otherwise there can be scenarios where masters and slaves (nodes) get out of sync, causing data-drift.

基于新的事務型資料字典，可靠性得到了提高。

This work is done in the context of the new, transactional data dictionary. See blog posts by Staale Deraas here and here.

原文釋出時間為：2018-05-30

本文作者：張銳志

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