database-deadlocks - 死锁管理

Question

我正在做一项研究，但很难找到任何相关信息。我偶然发现了这个问题：

为以下事务场景生成等待图并确定是否存在死锁。

交易：

T1
T2
T3
T4
T5
T6
T7
T8
T9
T10 

事务锁定的数据项：

X1,X2,X3
X4,X5,X6
X7,X8
X9,X10
X11,X12
X13,X14
X15
X1111 
X115
X199

数据项事务正在等待：

X4,X5,X6,X7
X7,X8,X9
X1,X10,X111
X7,X11,X12
X5
X6,X1,X2,X3,X11,X12
X5
X1,X115
X1
X11,X12

现在，就我在事务管理方面所见，这让我非常震惊。有人可以提供参考解释如何解决此类问题，或者无论如何提供帮助吗？

Answer 1

很常见的是，解决一些问题的关键是选择一个好的表示。如果您以表格形式表示您的问题：

T1 =>  { locked => [ qw( X1 X2 X3 ) ], waiting => [ qw( X4 X5 X6 X7         ) ] },
T2 =>  { locked => [ qw( X4 X5 X6 ) ], waiting => [ qw( X7 X8 X9            ) ] },
T3 =>  { locked => [ qw( X7 X8    ) ], waiting => [ qw( X1 X10 X111         ) ] },
T4 =>  { locked => [ qw( X9 X10   ) ], waiting => [ qw( X7 X11 X12          ) ] },
T5 =>  { locked => [ qw( X11 X12  ) ], waiting => [ qw( X5                  ) ] },
T6 =>  { locked => [ qw( X13 X14  ) ], waiting => [ qw( X6 X1 X2 X3 X11 X12 ) ] },
T7 =>  { locked => [ qw( X15      ) ], waiting => [ qw( X5                  ) ] },
T8 =>  { locked => [ qw( X1111    ) ], waiting => [ qw( X1 X115             ) ] },
T9 =>  { locked => [ qw( X115     ) ], waiting => [ qw( X1                  ) ] },
T10 => { locked => [ qw( X199     ) ], waiting => [ qw( X11 X12             ) ] },

然后你可以更有效地推理手头的问题。很容易看到某个事务正在等待什么资源，从那里你可以看到哪些事务持有这些资源。递归地应用该推理。如果你最终进入一个循环，你刚刚发现了一个死锁。

'当然，表示甚至可以更好：

use strict;
use warnings;

use Data::Dumper;

my %transactions = (
    T1 =>  { locked => [ qw( X1 X2 X3 ) ], waiting => [ qw( X4 X5 X6 X7         ) ] },
    T2 =>  { locked => [ qw( X4 X5 X6 ) ], waiting => [ qw( X7 X8 X9            ) ] },
    T3 =>  { locked => [ qw( X7 X8    ) ], waiting => [ qw( X1 X10 X111         ) ] },
    T4 =>  { locked => [ qw( X9 X10   ) ], waiting => [ qw( X7 X11 X12          ) ] },
    T5 =>  { locked => [ qw( X11 X12  ) ], waiting => [ qw( X5                  ) ] },
    T6 =>  { locked => [ qw( X13 X14  ) ], waiting => [ qw( X6 X1 X2 X3 X11 X12 ) ] },
    T7 =>  { locked => [ qw( X15      ) ], waiting => [ qw( X5                  ) ] },
    T8 =>  { locked => [ qw( X1111    ) ], waiting => [ qw( X1 X115             ) ] },
    T9 =>  { locked => [ qw( X115     ) ], waiting => [ qw( X1                  ) ] },
    T10 => { locked => [ qw( X199     ) ], waiting => [ qw( X11 X12             ) ] },
);

# get a data-item -> transaction mapping
my %items;
for my $transaction (keys %transactions) {
    for my $item (@{$transactions{$transaction}->{locked}}) {
            $items{$item} = $transaction;
    }
}

my @nodes;
my @edges;
for my $transaction (keys %transactions) {
    push @nodes, $transaction;
    for my $item (@{$transactions{$transaction}->{waiting}}) {
            push @edges, { source => $transaction, dest => $items{$item}, item => $item } if $items{$item};
    }
}

print "digraph tx_dependencies {\n";
print "    $_ label=$_;\n" for @nodes;
print "    @{[ $_->{source} ]} -> @{[ $_->{dest} ]} [label=@{[ $_->{item} ]}];\n" for @edges;
print "}\n";

该程序会生成一个 graphviz 文件，当对其进行适当的按摩时，dot最终结果为：