import mmap
import json
import random
import mysql.connector
import time
##公有变量
#dbinfos={
#   "db0":{'host':'192.168.42.60','user':'root','pwd':'Abcd1234','my_user':'root','my_pwd':'Abcd.1234',"port":3306,"database":"","role":"RW","weight":10,"status":1},
#   "db1":{'host':'192.168.42.61','user':'root','pwd':'Abcd1234','my_user':'root','my_pwd':'Abcd.1234',"port":3306,,"database":"":"R","weight":20,"status":1}
#   }
dbinfos={}
mmap_file = None
mmap_time=None
##这个函数返回json格式的字符串，也是实现初始化数据库信息的地方
##使用json格式是为了方便数据转换，从字符串---》二进制--》字符串---》字典
##如果采用其它方式共享dbinfos的方法，可以不用此方式
##配置库的地址
def get_json_str1():
 return json.dumps(dbinfos)
##读取配置库中的内容
def get_json_str():
 try:
  global dbinfos
  cnx = mysql.connector.connect(user='root', password='Abcd.1234',
        host='192.168.42.60',
        database='rwlb')
  cursor = cnx.cursor()
  cmdString="select * from rwlb"
  cnt=-1
  cursor.execute(cmdString)
  for (host,user,pwd,my_user,my_pwd,role,weight,status,port,db ) in cursor:
   cnt=cnt+1
   dict_db={'host':host,'user':user,'pwd':pwd,'my_user':my_user,'my_pwd':my_pwd,"port":port,"database":db,"role":role,"weight":weight,"status":status}
   dbinfos["db"+str(cnt)]=dict_db
  cursor.close()
  cnx.close()
  return json.dumps(dbinfos)
 except:
  cursor.close()
  cnx.close()
  return ""
##判断是否能正常连接到数据库
def check_conn_host():
 try:
  cnx = mysql.connector.connect(user='root', password='Abcd.1234',
        host='192.168.42.60',
        database='rwlb')
  cursor = cnx.cursor()
  cmdString="select user()"
  cnt=-1
  cursor.execute(cmdString)
  for user in cursor:
   cnt=len(user)
  cursor.close()
  cnx.close()
  return cnt
 except :
  return -1;
##select 属于读操作，其他属于写操作-----这里可以划分的更详细,比如执行存储过程等
def analyze_sql_state(sql):
 if "select" in sql:
  return "R"
 else:
  return "W"
##读取时间信息
def read_mmap_time():
 global mmap_time,mmap_file
 mmap_time.seek(0)
 ##初始时间
 inittime=int(mmap_time.read().translate(None, b'\x00').decode())
 ##当前时间
 endtime=int(time.time())
 ##时间差
 dis_time=endtime-inittime
 print("dis_time:"+str(dis_time))
 #重新读取数据
 if dis_time>10:
  ##当配置库正常的情况下才重新读取数据
  print(str(check_conn_host()))
  if check_conn_host()>0:   
   print("read data again")
   mmap_time.seek(0)
   mmap_file.seek(0)
   mmap_time.write(b'\x00')
   mmap_file.write(b'\x00')
   get_mmap_time()
   get_mmap_info()
  else:
   print("can not connect to host")   
 #不重新读取数据
 else:
  print("do not read data again")
##从内存中读取信息，
def read_mmap_info(sql):
 read_mmap_time()
 print("The data is in memory")
 global mmap_file,dict_db
 mmap_file.seek(0)
 ##把二进制转换为字符串
 info_str=mmap_file.read().translate(None, b'\x00').decode()
 #3把字符串转成json格式，方便后面转换为字典使用
 infos=json.loads(info_str) 
 host_count=len(infos)
 ##权重列表
 listw=[]
 ##总的权重数量
 wtotal=0
 ##数据库角色
 dbrole=analyze_sql_state(sql)
 ##根据权重初始化一个列表。这个是比较简单的算法，所以权重和控制在100以内比较好----这里可以选择其他比较好的算法
 for i in range(host_count):
  db="db"+str(i)
  if dbrole in infos[db]["role"]:
   if int(infos[db]["status"])==1:
    w=infos[db]["weight"]
    wtotal=wtotal+w
    for j in range(w):
     listw.append(i)
 if wtotal >0:
  ##产生一个随机数
  rad=random.randint(0,wtotal-1)
  ##读取随机数所在的列表位置的数据
  dbindex=listw[rad]
  ##确定选择的是哪个db
  db="db"+str(dbindex)
  ##为dict_db赋值，即选取的db的信息
  dict_db=infos[db]
  return dict_db
 else :
  return {}
##如果内存中没有时间信息，则向内存红写入时间信息
def get_mmap_time():
 global mmap_time
 ##第二个参数1024是设定的内存大小，单位：字节。如果内容较多，可以调大一点
 mmap_time = mmap.mmap(-1, 1024, access = mmap.ACCESS_WRITE, tagname = 'share_time')
 ##读取有效比特数，不包括空比特
 cnt=mmap_time.read_byte()
 if cnt==0:
  print("Load time to memory")
  mmap_time = mmap.mmap(0, 1024, access = mmap.ACCESS_WRITE, tagname = 'share_time')
  inittime=str(int(time.time()))
  mmap_time.write(inittime.encode())
##如果内存中没有对应信息，则向内存中写信息以供下次调用使用
def get_mmap_info():
 global mmap_file
 ##第二个参数1024是设定的内存大小，单位：字节。如果内容较多，可以调大一点
 mmap_file = mmap.mmap(-1, 1024, access = mmap.ACCESS_WRITE, tagname = 'share_mmap')
 ##读取有效比特数，不包括空比特
 cnt=mmap_file.read_byte()
 if cnt==0:
  print("Load data to memory")
  mmap_file = mmap.mmap(0, 1024, access = mmap.ACCESS_WRITE, tagname = 'share_mmap')
  mmap_file.write(get_json_str().encode())
##测试函数
def test1():
 get_mmap_time()
 get_mmap_info()
 for i in range(10):
  sql="select * from db"
  #sql="update t set col1=a where b=2"
  dbrole=analyze_sql_state(sql)
  dict_db=read_mmap_info(sql)
  print(dict_db["host"])
def test2():
 sql="select * from db"
 res=analyze_sql_state(sql)
 print("select:"+res)
 sql="update t set col1=a where b=2"
 res=analyze_sql_state(sql)
 print("update:"+res)
 sql="insert into t values(1,2)"
 res=analyze_sql_state(sql)
 print("insert:"+res)
 sql="delete from t where b=2"
 res=analyze_sql_state(sql)
 print("delete:"+res)
##类似主函数
if __name__=="__main__":
 test2()

 desc rwlb;
+---------+-------------+------+-----+---------+-------+
| Field | Type  | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| host | varchar(50) | YES |  | NULL |  |
| user | varchar(50) | YES |  | NULL |  |
| pwd  | varchar(50) | YES |  | NULL |  |
| my_user | varchar(50) | YES |  | NULL |  |
| my_pwd | varchar(50) | YES |  | NULL |  |
| role | varchar(10) | YES |  | NULL |  |
| weight | int(11)  | YES |  | NULL |  |
| status | int(11)  | YES |  | NULL |  |
| port | int(11)  | YES |  | NULL |  |
| db  | varchar(50) | YES |  | NULL |  |
+---------+-------------+------+-----+---------+-------+
select * from rwlb;
+---------------+------+----------+---------+-----------+------+--------+--------+------+------+
| host   | user | pwd  | my_user | my_pwd | role | weight | status | port | db |
+---------------+------+----------+---------+-----------+------+--------+--------+------+------+
| 192.168.42.60 | root | Abcd1234 | root | Abcd.1234 | RW |  10 |  1 | NULL | NULL |
| 192.168.42.61 | root | Abcd1234 | root | Abcd.1234 | R |  20 |  1 | NULL | NULL |
+---------------+------+----------+---------+-----------+------+--------+--------+------+------+