If I set the value of parameter 'log_transaction_sample_rate' as 0.7, how does it do the logging? Say I am running 10 transactions with 5 query each. How frequently the logging will happen on the basis of the above parameter. Let's ignore the other logging parameter settings.
Details from official documentation,
log_transaction_sample_rate (real)
Set the fraction of transactions whose statements are all logged, in addition to statements logged for other reasons. It applies to each new transaction regardless of its statements' durations. The default is 0, meaning not to log statements from any additional transaction. Setting this to 1 logs all statements for all transactions. log_transaction_sample_rate is helpful to track a sample of transaction. Only superusers can change this setting.