首页证明：Maximum data rate is affected by the bandwidth and signal-to-noise ratio of the channel.

证明：Maximum data rate is affected by the bandwidth and signal-to-noise ratio of the channel.

时间: 2024-06-05 11:10:23 浏览: 106

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 PostgreSQL 7.4 或更高版本  查询必须不是在一个显式的事务中（例如，不在 BEGIN ~ END 块中）  不能是 SELECT nextval 或者 SELECT setval  不能是 SELECT INTO  不能是 SELECT FOR UPDATE 或者 FOR SHARE  以 "SELECT" 开始或者为 COPY TO STDOUT, EXPLAIN, EXPLAIN ANALYZE SELECT... 其中一个， ignore_leading_white_space = true 将忽略开头的空格. 注意你可以通过在 SELECT 语句之前插入任意的注释来禁止负载均衡： /*REPLICATION*/ SELECT ... 请参考 replicate_select。也可以参考 flow chart。注：JDBC 驱动有自动提交的选项。如果自动提交为 false，则 JDBC 驱动将自己发送 "BEGIN" 和 "COMMIT"。因此 pgpool-II 无法做任何负载均衡。你需要调用 setAutoCommit(true) 来启用自动提交。复制模式中的故障切换 pgpool-II 退化一个死掉的后台并继续提供服务。只要最少还有一个后台还或者，服务就可以继续。复制模式中的特有错误在复制模式中，如果 pgpool 发现 INSERT，UPDATE 和 DELETE 生效的行数不同，如果 failover_if_affected_tuples_mismatch 被设置为 false，则 pgpool 将发送错误的 SQL 语句到所有的数据库节点来取消当前当前事务（如果为 false 则发生退化）。在这种情况下，你将在客户端终端中看到以下错误信息： =# UPDATE t SET a = a + 1; ERROR: pgpool detected difference of the number of update t uples Possible last query was: "update t1 set i = 1;" HINT: check data consistency between master and other db no de 你将在 PostgreSQL 的日志中看到更新的行数（在本例中，数据库节点 0 更新了 0 行而数据库节点 1 更新了 1 行）。 2010-07-22 13:23:25 LOG: pid 5490: SimpleForwardToFrontend: Number of affected tuples are: 0 1

The maximum data rate that can be transmitted through a communication channel is limited by the channel's bandwidth and signal-to-noise ratio (SNR). The bandwidth of a channel determines the maximum frequency of the signal that can be transmitted through it. The higher the bandwidth, the greater the maximum frequency of the signal and the faster data can be transmitted through the channel. On the other hand, the SNR of a channel is the ratio of the signal power to the noise power in the channel. The higher the SNR, the better the quality of the signal and the more data that can be transmitted through the channel without errors. The maximum data rate that can be achieved through a channel is given by the Shannon-Hartley theorem, which states that the maximum data rate is equal to the bandwidth of the channel multiplied by the logarithm of the SNR plus one. This formula shows that increasing the bandwidth or the SNR of the channel will increase the maximum data rate that can be achieved. Therefore, the maximum data rate is affected by the bandwidth and SNR of the channel.

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