PostgreSQL的日志文件
pg_log:数据库活动日志（也就是数据库的操作日志）；
pg_xlog:事务日志；
pg_clog:事务状态日志（pg_clog是pg_xlog的辅助日志）。
现在主要介绍pg_log
pg_log的文件内容是可以自定义的，可以通过命令来定义也可以通过修改配置文件postgresql.conf来定义.
主要需要修改的参数如下，参数修改完毕后重启服务，重新连接数据库，对其操作即可查看日志变化情况。
# - When to Log -
client_min_messages = info
#client_min_messages = notice # values in order of decreasing detail:
# debug5
# debug4
# debug3
# debug2
# debug1
# log
# notice
# warning
# error
log_min_messages = info
#log_min_messages = warning # values in order of decreasing detail:
# debug5
# debug4
# debug3
# debug2
# debug1
# info
# notice
# warning
# error
# log
# fatal
# panic
log_min_error_statement = info
#log_min_error_statement = error # values in order of decreasing detail:
# debug5
# debug4
# debug3
# debug2
# debug1
# info
# notice
# warning
# error
# log
# fatal
# panic (effectively off)
#log_min_duration_statement = -1 # -1 is disabled, 0 logs all statements
# and their durations, > 0 logs only
# statements running at least this number
# of milliseconds
# - What to Log -
#debug_print_parse = off
#debug_print_rewritten = off
#debug_print_plan = off
#debug_pretty_print = on
#log_checkpoints = off
log_connections = on
log_disconnections = on
#log_duration = off
log_error_verbosity = verbose # terse, default, or verbose messages
#log_hostname = off
log_line_prefix = '%a %u %d %h %t %i %e ' # special values:
# %a = application name
# %u = user name
# %d = database name
# %r = remote host and port（this is a os port）
# %h = remote host
# %p = process ID
# %t = timestamp without milliseconds
# %m = timestamp with milliseconds
# %i = command tag
# %e = SQL state
# %c = session ID
# %l = session line number
# %s = session start timestamp
# %v = virtual transaction ID
# %x = transaction ID (0 if none)
# %q = stop here in non-session
# processes
# %% = '%'
# e.g. '<%u%%%d> '
#log_lock_waits = off # log lock waits >= deadlock_timeout
log_statement = 'all' # none, ddl, mod, all
#log_temp_files = -1 # log temporary files equal or larger
# than the specified size in kilobytes;
# -1 disables, 0 logs all temp files
log_timezone = 'Asia/Hong_Kong'