默认情况下，X 插件支持 zstd、LZ4 和 Deflate 压缩算法。使用 Deflate 算法进行压缩是通过 zlib 软件库完成的，因此 X 协议连接的 deflate_stream 压缩算法设置等同于经典 MySQL 协议连接的 zlib 设置。By default, X Plugin supports the zstd, LZ4, and Deflate compression algorithms. Compression with the Deflate algorithm is carried out using the zlib software library, so the deflate_stream compression algorithm setting for X Protocol connections is equivalent to the zlib setting for classic MySQL protocol connections.

在服务器端，您可以通过将 mysqlx_compression_algorithms 系统变量设置为仅包含允许的算法来禁止任何压缩算法。算法名称 zstd_stream、lz4_message 和 deflate_stream 可以任意组合指定，顺序和大小写不重要。如果系统变量值为空字符串，则不允许任何压缩算法，连接将不进行压缩。On the server side, you can disallow any of the compression algorithms by setting the mysqlx_compression_algorithms system variable to include only those permitted. The algorithm names zstd_stream, lz4_message, and deflate_stream can be specified in any combination, and the order and lettercase are not important. If the system variable value is the empty string, no compression algorithms are permitted and connections are uncompressed.

下表比较了不同压缩算法的特性，并显示了它们的分配优先级。默认情况下，服务器会选择服务器和客户端共同允许的优先级最高的算法；客户端可以按照后面描述的方式更改优先级。客户端在指定算法时可以使用算法的简短别名。The following table compares the characteristics of the different compression algorithms and shows their assigned priorities. By default, the server chooses the highest-priority algorithm permitted in common by the server and the client; clients may change the priorities as described later. The short form alias for the algorithms can be used by clients when specifying them.

X 协议允许的压缩算法集（无论是用户指定的还是默认的）与 MySQL 服务器为经典 MySQL 协议连接允许的压缩算法集是独立的，经典 MySQL 协议连接允许的压缩算法集由 protocol_compression_algorithms 服务器系统变量指定。如果您没有指定 mysqlx_compression_algorithms 系统变量，X 插件不会回退使用经典 MySQL 协议连接的压缩设置。相反，其默认设置是允许 表 22.1，“X 协议压缩算法特性” 中显示的所有算法。这与 TLS 上下文的情况不同，TLS 上下文如果 X 插件系统变量未设置，则使用 MySQL 服务器设置，如 22.5.3 节，“使用 X 插件的加密连接” 所述。有关经典 MySQL 协议连接压缩的详细信息，请参见 6.2.8 节，“连接压缩控制”。The X Protocol set of permitted compression algorithms (whether user-specified or default) is independent of the set of compression algorithms permitted by MySQL Server for classic MySQL protocol connections, which is specified by the protocol_compression_algorithms server system variable. If you do not specify the mysqlx_compression_algorithms system variable, X Plugin does not fall back to using compression settings for classic MySQL protocol connections. Instead, its default is to permit all algorithms shown in Table 22.1, “X Protocol Compression Algorithm Characteristics”. This is unlike the situation for the TLS context, where MySQL Server settings are used if the X Plugin system variables are not set, as described in Section 22.5.3, “Using Encrypted Connections with X Plugin”. For information about compression for classic MySQL protocol connections, see Section 6.2.8, “Connection Compression Control”.

在客户端，X 协议连接请求可以指定多个用于压缩控制的参数：On the client side, an X Protocol connection request can specify several parameters for compression control:

连接模式具有以下允许值：The connection mode has these permitted values:

除了就每个连接商定压缩算法之外，服务器和客户端还可以从适用于商定算法的数值范围中达成压缩级别的共识。随着算法压缩级别的增加，数据压缩比也会增加，从而减少发送消息到客户端所需的网络带宽和传输时间。然而，数据压缩所需的努力也会增加，从而占用服务器的时间、CPU 和内存资源。压缩努力的增加与压缩比的增加并不呈线性关系。In addition to agreeing on a compression algorithm for each connection, the server and client can agree on a compression level from the numeric range that applies to the agreed algorithm. As the compression level for an algorithm increases, the data compression ratio increases, which reduces the network bandwidth and transfer time needed to send the message to the client. However, the effort required for data compression also increases, taking up time and CPU and memory resources on the server. Increases in the compression effort do not have a linear relationship to increases in the compression ratio.

客户端可以在与服务器进行 X 协议连接的能力协商期间请求特定的压缩级别。The client can request a specific compression level during capability negotiations with the server for an X Protocol connection.

MySQL 8.4 中 X 插件使用的默认压缩级别是通过性能测试选择的，被认为在压缩时间和网络传输时间之间达到了良好的平衡。这些默认值不一定与每种算法的库默认值相同。如果客户端没有为算法请求压缩级别，则适用这些默认值。默认压缩级别最初设置为 zstd 为 3，LZ4 为 2，Deflate 为 3。你可以使用 mysqlx_zstd_default_compression_level、mysqlx_lz4_default_compression_level 和 mysqlx_deflate_default_compression_level 系统变量来调整这些设置。The default compression levels used by X Plugin in MySQL 8.4 have been selected through performance testing as being a good trade-off between compression time and network transit time. These defaults are not necessarily the same as the library default for each algorithm. They apply if the client does not request a compression level for the algorithm. The default compression levels are initially set to 3 for zstd, 2 for LZ4, and 3 for Deflate. You can adjust these settings using the mysqlx_zstd_default_compression_level, mysqlx_lz4_default_compression_level, and mysqlx_deflate_default_compression_level system variables.

为了防止服务器过度消耗资源，X 插件为每种算法设置了服务器允许的最大压缩级别。如果客户端请求的压缩级别超过此设置，服务器将使用其允许的最大压缩级别（客户端的压缩级别请求仅由 MySQL Shell 支持）。最大压缩级别最初设置为 zstd 为 11，LZ4 为 8，Deflate 为 5。您可以使用 mysqlx_zstd_max_client_compression_level、mysqlx_lz4_max_client_compression_level 和 mysqlx_deflate_max_client_compression_level 系统变量来调整这些设置。To prevent excessive resource consumption on the server, X Plugin sets a maximum compression level that the server permits for each algorithm. If a client requests a compression level that exceeds this setting, the server uses its maximum permitted compression level (compression level requests by a client are supported only by MySQL Shell). The maximum compression levels are initially set to 11 for zstd, 8 for LZ4, and 5 for Deflate. You can adjust these settings using the mysqlx_zstd_max_client_compression_level, mysqlx_lz4_max_client_compression_level, and mysqlx_deflate_max_client_compression_level system variables.

如果服务器和客户端允许多个共同的算法，在协商过程中选择算法的默认优先顺序如表 22.1，“X 协议压缩算法特性”所示。对于支持指定压缩算法的客户端，连接请求可以包含客户端允许的一系列算法，使用算法名称或其别名指定。服务器将列表中算法的顺序视为优先顺序。在此情况下使用的算法是客户端列表中第一个同时在服务器端允许的算法。然而，压缩算法的选项受压缩模式的限制：If the server and client permit more than one algorithm in common, the default priority order for choosing an algorithm during negotiation is shown in Table 22.1, “X Protocol Compression Algorithm Characteristics”. For clients that support specifying compression algorithms, the connection request can include a list of algorithms permitted by the client, specified using the algorithm name or its alias. The order of these algorithms in the list is taken as a priority order by the server. The algorithm used in this case is the first of those in the client list that is also permitted on the server side. However, the option for compression algorithms is subject to the compression mode:

要监控消息压缩的效果，请使用X 插件连接压缩监控中描述的 X 插件状态变量。您可以使用这些状态变量来计算当前设置下消息压缩的好处，并利用这些信息调整您的设置。To monitor the effects of message compression, use the X Plugin status variables described in Monitoring Connection Compression for X Plugin. You can use these status variables to calculate the benefit of message compression with your current settings, and use that information to tune your settings.

X 协议连接压缩具有以下行为和边界：X Protocol connection compression operates with the following behaviors and boundaries:

您可以使用 X 插件状态变量来监控消息压缩的效果。当使用消息压缩时，会话 Mysqlx_compression_algorithm 状态变量显示当前 X 协议连接使用的压缩算法，而 Mysqlx_compression_level 显示所选择的压缩级别。You can monitor the effects of message compression using the X Plugin status variables. When message compression is in use, the session Mysqlx_compression_algorithm status variable shows which compression algorithm is in use for the current X Protocol connection, and Mysqlx_compression_level shows the compression level that was selected.

X 插件状态变量可用于计算所选压缩算法的效率（数据压缩比）以及使用消息压缩的整体效果。在以下计算中使用状态变量的会话值，以查看在已知压缩算法的特定会话中消息压缩的好处。或者使用状态变量的全局值，以检查服务器在所有使用 X 协议连接的会话中消息压缩的整体好处，包括这些会话使用的所有压缩算法，以及未使用消息压缩的所有会话。然后，您可以通过调整允许的压缩算法、最大压缩级别和默认压缩级别来优化消息压缩，如 为 X 插件配置连接压缩 中所述。X Plugin status variables can be used to calculate the efficiency of the compression algorithms that are selected (the data compression ratio), and the overall effect of using message compression. Use the session value of the status variables in the following calculations to see what the benefit of message compression was for a specific session with a known compression algorithm. Or use the global value of the status variables to check the overall benefit of message compression for your server across all sessions using X Protocol connections, including all the compression algorithms that have been used for those sessions, and all sessions that did not use message compression. You can then tune message compression by adjusting the permitted compression algorithms, maximum compression level, and default compression level, as described in Configuring Connection Compression for X Plugin.

当使用消息压缩时，Mysqlx_bytes_sent 状态变量显示从服务器发送的字节总数，包括压缩消息的负载（在压缩后测量）、所有未被压缩的消息项（例如 X 协议头）以及任何未压缩的消息。Mysqlx_bytes_sent_compressed_payload 状态变量显示作为压缩消息负载发送的字节总数（在压缩后测量），而 Mysqlx_bytes_sent_uncompressed_frame 状态变量显示同一消息负载的字节总数，但在压缩前测量。因此，可以使用以下公式计算压缩比，该比值显示压缩算法的效率：When message compression is in use, the Mysqlx_bytes_sent status variable shows the total number of bytes sent out from the server, including compressed message payloads measured after compression, any items in compressed messages that were not compressed such as X Protocol headers, and any uncompressed messages. The Mysqlx_bytes_sent_compressed_payload status variable shows the total number of bytes sent as compressed message payloads, measured after compression, and the Mysqlx_bytes_sent_uncompressed_frame status variable shows the total number of bytes for those same message payloads but measured before compression. The compression ratio, which shows the efficiency of the compression algorithm, can therefore be calculated using the following expression:

mysqlx_bytes_sent_uncompressed_frame / mysqlx_bytes_sent_compressed_payload

服务器发送的 X 协议消息的压缩效果可以使用以下表达式计算：The effectiveness of compression for X Protocol messages sent by the server can be calculated using the following expression:

(mysqlx_bytes_sent - mysqlx_bytes_sent_compressed_payload + mysqlx_bytes_sent_uncompressed_frame) / mysqlx_bytes_sent

对于服务器从客户端接收的消息，Mysqlx_bytes_received_compressed_payload 状态变量显示以压缩消息负载形式接收的字节总数（在解压缩前测量），而 Mysqlx_bytes_received_uncompressed_frame 状态变量显示相同消息负载的字节总数，但在解压缩后测量。Mysqlx_bytes_received 状态变量包括在解压缩前测量的压缩消息负载、压缩消息中的任何未压缩项，以及任何未压缩的消息。For messages received by the server from clients, the Mysqlx_bytes_received_compressed_payload status variable shows the total number of bytes received as compressed message payloads, measured before decompression, and the Mysqlx_bytes_received_uncompressed_frame status variable shows the total number of bytes for those same message payloads but measured after decompression. The Mysqlx_bytes_received status variable includes compressed message payloads measured before decompression, any uncompressed items in compressed messages, and any uncompressed messages.