230608 11:57:17 innobackupex: Starting the backup operation IMPORTANT: Please check that the backup run completes successfully. At the end of a successful backup run innobackupex prints "completed OK!". 230608 11:57:17 version_check Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_group=xtrabackup;mysql_socket=/var/lib/mysql/mysql.sock' as 'root' (using password: YES). 230608 11:57:17 version_check Connected to MySQL server 230608 11:57:17 version_check Executing a version check against the server... 230608 11:57:17 version_check Done. 230608 11:57:17 Connecting to MySQL server host: localhost, user: root, password: set, port: 0, socket: /var/lib/mysql/mysql.sock Error: Unsupported server version: '5.7.42-log'. Please report a bug at https://bugs.launchpad.net/percona-xtrabackup

根据你提供的信息，innobackupex 在执行备份时出现了错误。错误信息中提到了 "Unsupported server version: '5.7.42-log'"，这意味着你的 MySQL 服务器版本不被支持。

你需要升级 innobackupex 或降低 MySQL 服务器版本以解决这个问题。另外，备份完成后请务必检查备份运行是否成功，innobackupex 应该会在备份成功后输出 "completed OK!"。

相关问题

xtrabackup: recognized server arguments: --datadir=/var/lib/mysql xtrabackup: recognized client arguments: 230609 18:37:44 innobackupex: Starting the backup operation IMPORTANT: Please check that the backup run completes successfully. At the end of a successful backup run innobackupex prints "completed OK!". 230609 18:37:44 version_check Connecting to MySQL server with DSN 'dbi:mysql:;mysql_read_default_group=xtrabackup' as 'ser=root' (using password: YES). Failed to connect to MySQL server: DBI connect(';mysql_read_default_group=xtrabackup','ser=root',...) failed: Access denied for user 'ser=root'@'localhost' (using password: YES) at - line 1314. 230609 18:37:44 Connecting to MySQL server host: localhost, user: ser=root, password: set, port: not set, socket: not set Failed to connect to MySQL server: Access denied for user 'ser=root'@'localhost' (using password: YES).

这个错误提示显示在使用xtrabackup工具备份MySQL数据库时出现了连接MySQL服务器的错误，无法连接到MySQL服务器。

错误提示中指出连接MySQL服务器失败的原因是访问被拒绝，可能原因包括：

1. 用户名或密码错误。
2. MySQL服务器拒绝了该用户的连接请求。
3. 防火墙或网络设置阻止了MySQL服务器的访问。

您可以检查备份命令中MySQL服务器的用户名和密码是否正确，并确保该用户有足够的权限连接和备份MySQL服务器。如果用户信息正确，请检查MySQL服务器的日志以获取更多信息，或者检查网络和防火墙设置以确保MySQL服务器的访问被允许。

Implement a Matlab function which completes the following task: Give the minimax approximation of a given function f on (a a closed interval; (b)a set of finitely many points.

Here is an implementation of a Matlab function that calculates the minimax approximation of a given function f on a closed interval [a,b] using a set of finitely many points:

function [p, err] = minimax(f, a, b, n)
% MINIMAX Approximation of f on [a,b] with n points using minimax method
% p is the polynomial and err is the maximum error

% Create Chebyshev nodes
x = cos((0:n-1)*pi/(n-1))';
x = 0.5*(a+b) + 0.5*(b-a)*x;

% Calculate Chebyshev coefficients
c = chebcoeffs(f, x);

% Construct minimax polynomial
p = chebval(x, c);

% Calculate maximum error
err = max(abs(f(x) - p));
end

function c = chebcoeffs(f, x)
% CHEBCOEFFS Calculate Chebyshev coefficients of f at nodes x

% Chebyshev polynomials
n = length(x);
T = zeros(n,n);
T(:,1) = ones(n,1);
T(:,2) = x;

for k = 3:n
    T(:,k) = 2*x.*T(:,k-1) - T(:,k-2);
end

% Inner product matrix
A = T'*T;

% Right-hand side vector
b = T'*f(x);

% Chebyshev coefficients
c = A\b;
end

To use this function, simply provide the function `f`, the interval endpoints `a` and `b`, and the number of points `n` to use in the approximation. The function returns the minimax polynomial `p` and the maximum error `err`.

Note that this implementation uses Chebyshev nodes and Chebyshev polynomials to construct the minimax polynomial. Chebyshev nodes are known to give the best possible approximation in the minimax sense, and Chebyshev polynomials are used as the basis functions because they are orthogonal with respect to the L2 inner product.