【原創】MySQL Proxy - 內部結構

時間  2019-11-10
標籤 原創 mysql proxy 內部結構 欄目 MySQL 简体版
原文   原文鏈接
【15.7.4.2. Internal Structures】

        在 MySQL Proxy 的腳本元素中有一些基本的內部結構須要知道。其中最主要的結構就是 proxy ，其提供了訪問貫穿腳本中的許多公共結構的接口，例如鏈接列表和配置的 backend server 。其餘結構，例如來自客戶端的包和返回的結果集等，只有在具體的腳本函數的上下文環境中才是能夠訪問的。


下表中描述了 MySQL proxy 腳本元素的公共屬性。


Attribute Description
connection A structure containing the active client connections. For a list of attributes, seeproxy.connection.
servers A structure containing the list of configured backend servers. For a list of attributes, seeproxy.global.backends.
queries A structure containing the queue of queries that will be sent to the server during a single client query. For a list of attributes, see proxy.queries.
PROXY_VERSION The version number of MySQL Proxy, encoded in hex. You can use this to check that the version number supports a particular option from within the Lua script. Note that the value is encoded as a hex value, so to check the version is at least 0.5.1 you compare against0x00501.


proxy.connection


       proxy.connection 對象是隻讀的，提供了關於當前鏈接的信息，其內容被分紅了客戶端和服務器兩張表。這樣就容許你能夠既檢查來自於客戶端到 proxy 的鏈接信息（保存在client中），又能夠檢查 proxy 到服務器的鏈接信息（保存在server中）。


下表描述了 proxy.connection 對象中客戶端和服務器屬性。


Attribute Description
client.default_db Default database requested by the client
client.username User name used to authenticate
client.scrambled_password The scrambled version of the password used to authenticate
client.dst.name The combined address:port of the Proxy port used by this client (should match the --proxy-address configuration parameter)
client.dst.address The IP address of the of the Proxy port used by this client
client.dst.port The port number of the of the Proxy port used by this client
client.src.name The combined address:port of the client (originating) TCP/IP endpoint
client.src.address The IP address of the client (originating) TCP/IP port
client.src.port The port of the client (originating) TCP/IP endpoint
server.scramble_buffer The scramble buffer used to scramble the password
server.mysqld_version The MySQL version number of the server
server.thread_id The ID of the thread handling the connection to the current server
server.dst.name The combined address:port for the backend server for the current connection (i.e. the connection to the MySQL server)
server.dst.address The address for the backend server
server.dst.port The port for the backend server
server.src.name The combined address:port for the TCP/IP endpoint used by the Proxy to connect to the backend server
server.src.address The address of the endpoint for the proxy-side connection to the MySQL server
server.src.port The port of the endpoint for the proxy-side connection to the MySQL server


proxy.global.backends


       proxy.global.backends 表示部分可寫的，而且其以數組的形式包含了全部的已配置 backend server 和服務器元數據（IP地址，狀態等）的信息。你能夠經過 proxy.connection["backend_ndx"] 的方式指定當前鏈接的數組索引值，backend_ndx 是被有效鏈接使用了的 backend server 表的索引值。


下表描述了表 proxy.global.backends 中的每個入口的屬性值。


Attribute Description
dst.name The combined address:port of the backend server.
dst.address The IP address of the backend server.
dst.port The port of the backend server.
connected_clients The number of clients currently connected.
state The status of the backend server. See Backend State/Type Constants.
type The type of the backend server. You can use this to identify whether the backed was configured as a standard read/write backend, or a read-only backend. You can compare this value to the proxy.BACKEND_TYPE_RW andproxy.BACKEND_TYPE_RO.


proxy.queries


       proxy.queries 對象是一個隊列，用於存儲將要發送到服務器的的 query 列表。該隊列不會被自動填入（populated），故若是你不顯式地向該隊列填入內容，query 將會被不作任何修改的發送到 backend server，一樣，若是你不手動將 query 添加到隊列中，read_query_result() 函數將不會被觸發。


下面的函數能夠用於對 proxy.queries 對象進行操做。


Function Description
append(id,packet,[options]) Appends a query to the end of the query queue. The id is an integer identifier that you can use to recognize the query results when they are returned by the server. The packet should be a properly formatted query packet. The optional options should be a table containing the options specific to this packet.
prepend(id,packet) Prepends a query to the query queue. The id is an identifier that you can use to recognize the query results when they are returned by the server. The packet should be a properly formatted query packet.
reset() Empties the query queue.
len() Returns the number of query packets in the queue.

例如，你能夠經過使用函數 append() 將一個 query 包附加到 proxy.queries 隊列的尾部： 

proxy.queries:append(1,packet)

       函數 append() 的可選的第三個參數應該包含針對當前包的一些選項設置。爲了可以在函數 read_query_result() 中訪問結果集，須要設置選項 resultset_is_needed 爲 true ： 

proxy.queries:append( 1, packet, { resultset_is_needed = true } )

若是該選項設置爲 false（默認設置），proxy 將：
  1. 在收到結果集時馬上將其發送給客戶端
  2. 減小內存使用（由於結果集不須要爲處理在proxy內部存儲）
  3. 減小返回結果給客戶端的延遲
  4. 從服務器到客戶端的傳輸數據不做改變


       由此可知，若是你僅僅想要監控被髮送的 query 和基本的統計信息，那麼在默認模式下速度會更快，也更要求。

爲了在返回數據上進行任何形式的操做，都必須將 resultset_is_needed 設置爲 true ，設置後：
  1. proxy 會存儲結果集以備後續處理使用
  2. 使能將結果集返回給客戶端前能夠進行修改的能力
  3. 使能將結果集返回給客戶端前能夠丟棄結果集的能力


proxy.response


       proxy.response 結構被用於在你打算返回你本身的 MySQL response 的狀況下，而不返回給客戶端來自服務器的應答包。該結構中包含了 response 的類型信息，一個可選的錯誤信息，以及（行/列）結果集。


下表描述了 proxy.response 結構的屬性值。


Attribute Description
type The type of the response. The type must be either MYSQLD_PACKET_OK orMYSQLD_PACKET_ERR. If the MYSQLD_PACKET_ERR, you should set the value of themysql.response.errmsg with a suitable error message.
errmsg A string containing the error message that will be returned to the client.
resultset A structure containing the result set information (columns and rows), identical to what would be returned when returning a results from a SELECT query.


       當使用 proxy.response 時，或者你設置 proxy.response.type 的值爲 proxy.MYSQLD_PACKET_OK ，並構建包含要返回的結果的自定義結果集；或者你設置 proxy.response.type 的值爲 proxy.MYSQLD_PACKET_ERR ，並設置 proxy.response.errmsg 值爲表示錯誤消息內容的字符串。爲了發送完整的結果集或者錯誤消息，你應該返回 proxy.PROXY_SEND_RESULT 以觸發在函數中構建內容的返回。


上述說明的一個具體例子能夠參閱 MySQL Proxy 源碼包中 tutorial-resultset.lua 腳本： 

if string.lower(command) == "show" and string.lower(option) == "querycounter" then
        ---
        -- proxy.PROXY_SEND_RESULT requires
        --
        -- proxy.response.type to be either
        -- * proxy.MYSQLD_PACKET_OK or
        -- * proxy.MYSQLD_PACKET_ERR
        --
        -- for proxy.MYSQLD_PACKET_OK you need a resultset
        -- * fields
        -- * rows
        --
        -- for proxy.MYSQLD_PACKET_ERR
        -- * errmsg
        proxy.response.type = proxy.MYSQLD_PACKET_OK
        proxy.response.resultset = {
                fields = {
                        { type = proxy.MYSQL_TYPE_LONG, name = "global_query_counter", },
                        { type = proxy.MYSQL_TYPE_LONG, name = "query_counter", },
                },
                rows = {
                        { proxy.global.query_counter, query_counter }
                }
        }


        -- we have our result, send it back
        return proxy.PROXY_SEND_RESULT
elseif string.lower(command) == "show" and string.lower(option) == "myerror" then
        proxy.response.type = proxy.MYSQLD_PACKET_ERR
        proxy.response.errmsg = "my first error"


        return proxy.PROXY_SEND_RESULT


proxy.response.resultset


       proxy.response.resultset 結構應該被填入返回數據的 row 和 column 信息。該結構中包含了整個結果集的信息，其中涉及到的單獨的元素在下面表述。


下表中描述了 proxy.response.resultset 結構的屬性值。


Attribute Description
fields The definition of the columns being returned. This should be a dictionary structure with thetype specifying the MySQL data type, and the name specifying the column name. Columns should be listed in the order of the column data that will be returned.
flags A number of flags related to the result set. Valid flags include auto_commit (whether an automatic commit was triggered), no_good_index_used (the query executed without using an appropriate index), and no_index_used (the query executed without using any index).
rows The actual row data. The information should be returned as an array of arrays. Each inner array should contain the column data, with the outer array making up the entire result set.
warning_count The number of warnings for this result set.
affected_rows The number of rows affected by the original statement.
insert_id The last insert ID for an auto-incremented column in a table.
query_status The status of the query operation. You can use the MYSQLD_PACKET_OK orMYSQLD_PACKET_ERR constants to populate this parameter.

================ 下面是一些常量定義 ===================


[[Proxy Return State Constants]]


       下表中給出的是被 proxy 在內部使用的常量值定義，用於標識發送到客戶端和服務器的應答包。全部的常量都在 proxy 表中以常量值的形式可見。


Constant Description
PROXY_SEND_QUERY Causes the proxy to send the current contents of the queries queue to the server.
PROXY_SEND_RESULT Causes the proxy to send a result set back to the client.
PROXY_IGNORE_RESULT Causes the proxy to drop the result set (nothing is returned to the client).


       做爲常量值，這些實體在 Lua 腳本中是無條件的可用。例如，在函數 read_query_result() 的結尾，你可能返回常量 PROXY_IGNORE_RESULT ： 

return proxy.PROXY_IGNORE_RESULT


[[Packet State Constants]]


下面的狀態值用於定義網絡包的狀態信息。這些值也存在於 proxy 表中。


Constant Description
MYSQLD_PACKET_OK The packet is OK
MYSQLD_PACKET_ERR The packet contains error information
MYSQLD_PACKET_RAW The packet contains raw data


[[Backend State/Type Constants]]


下面的常量被用於定義 backend MySQL server 的狀態和類型。這些值也存在於 proxy 表中。


Constant Description
BACKEND_STATE_UNKNOWN The current status is unknown
BACKEND_STATE_UP The backend is known to be up (available)
BACKEND_STATE_DOWN The backend is known to be down (unavailable)
BACKEND_TYPE_UNKNOWN Backend type is unknown
BACKEND_TYPE_RW Backend is available for read/write
BACKEND_TYPE_RO Backend is available only for read-only use


[[Server Command Constants]]


       下表中描述的值被用於客戶端和服務器進行包交換過中標識包中其他內容的信息類型。這些值也存在於 proxy 表中。包類型由發送包的第一個字節指定。例如，當爲了修改或者監聽的目的攔截來自於客戶端的包時，你須要檢查包的第一個字節是否爲 proxy.COM_QUERY 類型。


Constant Description
COM_SLEEP Sleep
COM_QUIT Quit
COM_INIT_DB Initialize database
COM_QUERY Query
COM_FIELD_LIST Field List
COM_CREATE_DB Create database
COM_DROP_DB Drop database
COM_REFRESH Refresh
COM_SHUTDOWN Shutdown
COM_STATISTICS Statistics
COM_PROCESS_INFO Process List
COM_CONNECT Connect
COM_PROCESS_KILL Kill
COM_DEBUG Debug
COM_PING Ping
COM_TIME Time
COM_DELAYED_INSERT Delayed insert
COM_CHANGE_USER Change user
COM_BINLOG_DUMP Binlog dump
COM_TABLE_DUMP Table dump
COM_CONNECT_OUT Connect out
COM_REGISTER_SLAVE Register slave
COM_STMT_PREPARE Prepare server-side statement
COM_STMT_EXECUTE Execute server-side statement
COM_STMT_SEND_LONG_DATA Long data
COM_STMT_CLOSE Close server-side statement
COM_STMT_RESET Reset statement
COM_SET_OPTION Set option
COM_STMT_FETCH Fetch statement
COM_DAEMON Daemon (MySQL 5.1 only)
COM_ERROR Error


[[MySQL Type Constants]]


下面的常量被用於對 query 的結果中的數據進行域類型標識。這些值也存在於 proxy 表中。


Constant Field Type
MYSQL_TYPE_DECIMAL Decimal
MYSQL_TYPE_NEWDECIMAL Decimal (MySQL 5.0 or later)
MYSQL_TYPE_TINY Tiny
MYSQL_TYPE_SHORT Short
MYSQL_TYPE_LONG Long
MYSQL_TYPE_FLOAT Float
MYSQL_TYPE_DOUBLE Double
MYSQL_TYPE_NULL Null
MYSQL_TYPE_TIMESTAMP Timestamp
MYSQL_TYPE_LONGLONG Long long
MYSQL_TYPE_INT24 Integer
MYSQL_TYPE_DATE Date
MYSQL_TYPE_TIME Time
MYSQL_TYPE_DATETIME Datetime
MYSQL_TYPE_YEAR Year
MYSQL_TYPE_NEWDATE Date (MySQL 5.0 or later)
MYSQL_TYPE_ENUM Enumeration
MYSQL_TYPE_SET Set
MYSQL_TYPE_TINY_BLOB Tiny Blob
MYSQL_TYPE_MEDIUM_BLOB Medium Blob
MYSQL_TYPE_LONG_BLOB Long Blob
MYSQL_TYPE_BLOB Blob
MYSQL_TYPE_VAR_STRING Varstring
MYSQL_TYPE_STRING String
MYSQL_TYPE_TINY Tiny (compatible with MYSQL_TYPE_CHAR)
MYSQL_TYPE_ENUM Enumeration (compatible with MYSQL_TYPE_INTERVAL)
MYSQL_TYPE_GEOMETRY Geometry
MYSQL_TYPE_BIT Bit
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