postgresql.conf 部分参数说明
checkpoint参数描述：
checkpoint的时候会将所有的脏数据都flush到磁盘上
checkpoint_timeout：
两次checkpoint间隔时长
checkpoint_segments:
两次checkpoint间隔最大的xlog日志文件数量(指的是pg_xlog下的文件：000000010000000000000007)以日志文件段（每个段通常 16 兆大）计。
walwriter进程参数描述：
fsync：
该参数直接控制wal日志是否先写入磁盘，然后在更新数据。批量更新/插入时刻off此项，加快执行速度。（off不影响wal writer process 进程运行）
synchronous_commit：
flush wal日志到xlog后才给xact（事务）返回信息。此参数也控制流复制是同步还是异步。
wal_sync_method：
wal日志写到磁盘的控制方式。
full_page_writes：
是否将wal日志一个page整个写入磁盘。好处不会有数据一半写入另一半崩溃时未来得及未写入,不好恢复。
wal_buffers：
wal日志缓冲区大小最小是32K（4个page）。
wal_writer_delay：
两次wal日志缓冲区flush到磁盘间隔时长。
commit_delay：
已经提交的数据在wal缓冲区存放的时长。（为了等够了一定数额一并提交）
commit_siblings：
超过这个数值就将wal缓冲区应该提交的一并flush到磁盘。（参见
commit_delay
）
归档：
archive_mode:
归档命令。
archive_command：
将xlog拷贝到一个地方的命令。
#------------------------------------------------------------------------------
# FILE LOCATIONS
#------------------------------------------------------------------------------
# The default values of these variables are driven from the -D command-line
# option or PGDATA environment variable, represented here as ConfigDir.
#data_directory = 'ConfigDir' # use data in another directory
# (change requires restart)
#hba_file = 'ConfigDir/pg_hba.conf' # host-based authentication file
# (change requires restart)
...skipping...
#fsync = on # turns forced synchronization on or off
#synchronous_commit = on # synchronization level;
# off, local, remote_write, or on
#wal_sync_method = fsync # the default is the first option
# supported by the operating system:
# open_datasync
# fdatasync (default on Linux)
# fsync
# fsync_writethrough
# open_sync
#full_page_writes = on # recover from partial page writes
#wal_buffers = -1 # min 32kB, -1 sets based on shared_buffers
# (change requires restart)
#wal_writer_delay = 200ms # 1-10000 milliseconds
#commit_delay = 0 # range 0-100000, in microseconds
#commit_siblings = 5 # range 1-1000
# - Checkpoints -
checkpoint_segments = 16 # in logfile segments, min 1, 16MB each
#checkpoint_timeout = 5min # range 30s-1h
#checkpoint_completion_target = 0.5 # checkpoint target duration, 0.0 - 1.0
#checkpoint_warning = 30s # 0 disables
# - Archiving -
archive_mode = on # allows archiving to be done
# (change requires restart)
archive_command = 'cp %p /home/pg93/test_rep/arch/%f' # command to use to archive a logfile segment
# placeholders: %p = path of file to archive
# %f = file name only
# e.g. 'test ! -f /mnt/server/archivedir/%f && cp %p /mnt/server/archivedir/%f'
#archive_timeout = 0 # force a logfile segment switch after this
# number of seconds; 0 disables
流复制：
max_wal_senders:
允许多少个流复制协议连接过来。一个流复制协议会产生一个walsender进程（一个master可能会有多个standby节点进行流复制）。
wal_keep_segments：
xlog目录中最多容纳多少个wal日志文件，超过了则删掉最初的几个。（一个日志文件16M）
synchronous_standby_names：
同步流复制允许standby节点的名字。（'*' = all）
hot_standby：
standby节点是否允许执行SQL查询。
max_standby_archive_delay&max_standby_streaming_delay：
standby节点查询表A时master节点已经删除了此表，则会发生冲突（因为standby节点必须replies），此参数就是等待冲突解决的时长。
wal_receiver_status_interval：
反馈给主节点自己已经接受（
replies
）到数据信息。
hot_standby_feedback：
如果standby和master发生了冲突是否将此冲突信息反馈给master。
#------------------------------------------------------------------------------
# REPLICATION
#------------------------------------------------------------------------------
# - Sending Server(s) -
# Set these on the master and on any standby that will send replication data.
max_wal_senders = 13 # max number of walsender processes
# (change requires restart)
wal_keep_segments = 16 # in logfile segments, 16MB each; 0 disables
#wal_sender_timeout = 60s # in milliseconds; 0 disables
# - Master Server -
# These settings are ignored on a standby server.
#synchronous_standby_names = '' # standby servers that provide sync rep
# comma-separated list of application_name
# from standby(s); '*' = all
#vacuum_defer_cleanup_age = 0 # number of xacts by which cleanup is delayed
# - Standby Servers -
# These settings are ignored on a master server.
#hot_standby = off # "on" allows queries during recovery
# (change requires restart)
#max_standby_archive_delay = 30s # max delay before canceling queries
# when reading WAL from archive;
# -1 allows indefinite delay
#max_standby_streaming_delay = 30s # max delay before canceling queries
# when reading streaming WAL;
# -1 allows indefinite delay
#wal_receiver_status_interval = 10s # send replies at least this often
# 0 disables
#hot_standby_feedback = off # send info from standby to prevent
# query conflicts
#wal_receiver_timeout = 60s # time that receiver waits for
# communication from master
# in milliseconds; 0 disables
log_autovacuum_min_duration:
在规定时长内未完成的vacuum予以记录日志
autovacuum_max_workers：
允许同事开启的vacuum进程数
autovacuum_naptime：
两次vacuum间隔时间
autovacuum_vacuum_threshold：
达到某表DML操作的最小行数则vacuum
autovacuum_analyze_threshold:
激活自动analyze操作的最小行数，analyze有利于对SQL语句进行更精准的plan(这是由于explain用到的pg_class列reltuples and relpages are not updated on-the-fly)
autovacuum_vacuum_scale_factor：
表示autovacuum的vacuum操作所需的变更量阈值,当这个表的update/delete的tuple总数大于(pg_class.reltuples*autovacuum_vacuum_scale_factor+autovacuum_vacuum_threshold)时, 触发vacuum操作. http://www.postgresql.org/docs/9.2/static/routine-vacuuming.html#AUTOVACUUM
autovacuum_analyze_scale_factor：
表示autovacuum的analyze操作所需的变更量阈值,当这个表的INSERT/update/delete的tuple总数大于(pg_class.reltuples*autovacuum_analyze_scale_factor+autovacuum_analyze_threshold)时, 触发analyze操作
autovacuum_freeze_max_age：
某表的pg_class.relfrozenxid的最大值，如果超出此值则重置xid
autovacuum_vacuum_cost_delay：
运行一次vacuum的时长，如果超过此值则休眠然后起来接着vacuum(vacuum很好I/O)
#log_autovacuum_min_duration = -1 # -1 disables, 0 logs all actions and
# their durations, > 0 logs only
# actions running at least this number
# of milliseconds.
#autovacuum_max_workers = 3 # max number of autovacuum subprocesses
# (change requires restart)
#autovacuum_naptime = 1min # time between autovacuum runs
#autovacuum_vacuum_threshold = 50 # min number of row updates before
# vacuum
#autovacuum_analyze_threshold = 50 # min number of row updates before
# analyze
#autovacuum_vacuum_scale_factor = 0.2 # fraction of table size before vacuum
#autovacuum_analyze_scale_factor = 0.1 # fraction of table size before analyze
#autovacuum_freeze_max_age = 200000000 # maximum XID age before forced vacuum
# (change requires restart)
#autovacuum_multixact_freeze_max_age = 400000000 # maximum Multixact age
# before forced vacuum
# (change requires restart)
#autovacuum_vacuum_cost_delay = 20ms # default vacuum cost delay for
# autovacuum, in milliseconds;
# -1 means use vacuum_cost_delay
#autovacuum_vacuum_cost_limit = -1 # default vacuum cost limit for
# autovacuum, -1 means use
# vacuum_cost_limit