TimesTen 应用层数据库缓存学习：6. Aging策略

declare a number := 1;
begin
select max(a) into :a from lru_tab;
a := a+1;
insert into lru_tab values(a, sysdate);
end;
/

Aging基本概念

Aging就是缓存的老化策略，毕竟缓存不能容纳所有的数据库数据，因此根据Aging设置，一些数据在某些时刻会退出缓存

TimesTen中, Aging既可以用于普通的表，也可以用于cache group。对于cache group，Aging在root table定义，影响整个cache instance。
为了简便，以下的例子都使用普通表来做示例。

TimesTen Aging支持基于LRU(least recently used）基于时间两种方式.

Aging 常用命令

time based aging:

create table tbaging (a int, ts timestamp not null) AGING USE ts LIFETIME 1 MINUTES CYCLE 1 MINUTES ON;

LRU aging:

create table lru_tab(a int primary key not null, b date not null) aging lru on;

LRU aging策略设置

call ttAgingLRUConfig;
call ttAgingLRUConfig(.2, .3, 1);

强制启动Aging（无论定义了Aging的表设置Aging为on还是off）

call ttAgingScheduleNow(); <-所有定义了aging的表
call ttAgingScheduleNow('tablename')

Aging的开通，开启，关闭

alter table tablename add aging lru on alter table tablename drop aging alter table tablename set aging on|off alter table tablename add aging use columnname lifetime 3600 seconds cycle 5 seconds ON alter table tablename set aging lifetime 2 days;
alter table tablename set aging cycle 5 seconds

Aging监控

tttracemon DSN
Trace> level aging 3
Trace> flush
Trace> dump
...
Trace> level aging 0
Trace> quit

LRU Aging

LRU Aging删除最老的记录，以保持内存维持在一个水平。
可以用ttAgingLRUConfig([LowUsageThreshHold], [LowUsageThreshHold], [AgingCycle])设置LRU Aging属性。
其中低于LowUsageThreshHold就关闭Aging，高于LowUsageThreshHold就开始Aging，AgingCycle为检查频率，整数，至少为1分钟。

LRU aging can be defined for all cache group types except explicitly loaded autorefresh cache groups. LRU aging is defined by default on dynamic cache groups.

Command> create table lru_tab(a int primary key not null, b date not null) aging lru on;
Command> desc lru_tab;

Table ORACLE.LRU_TAB:
  Columns:
   *A                               NUMBER (38) NOT NULL
    B                               DATE NOT NULL
  Aging: LRU on

1 table found.
(primary key columns are indicated with *)

Command> dssize;

  PERM_ALLOCATED_SIZE:      40960
  PERM_IN_USE_SIZE:         9545
  PERM_IN_USE_HIGH_WATER:   31652
  TEMP_ALLOCATED_SIZE:      131072
  TEMP_IN_USE_SIZE:         94674
  TEMP_IN_USE_HIGH_WATER:   95197


Command> call ttAgingLRUConfig;
< .8000000, .9000000, 1 > <- 缺省值
1 row found.

Command> select 9545/40960 from dual;
< .2330322265625 >
1 row found.

Command> call ttAgingLRUConfig(.2, .3, 1);
< .2000000, .3000000, 1 >
1 row found.

Command> insert into lru_tab values(1, sysdate);
1 row inserted.

Command> select * from lru_tab;
< 1, 2016-04-13 22:31:38 >
1 row found.

declare a number := 1;
begin
  select max(a) into a from lru_tab;
  for i in 1..100000 loop  
    a := a+1;
    insert into lru_tab values(a, sysdate);
  end loop;
end;
/

PL/SQL procedure successfully completed. Command> select count(*) from lru_tab;
< 100001 >
1 row found.
Command> dssize;

  PERM_ALLOCATED_SIZE:      40960
  PERM_IN_USE_SIZE:         15032
  PERM_IN_USE_HIGH_WATER:   31652
  TEMP_ALLOCATED_SIZE:      131072
  TEMP_IN_USE_SIZE:         94611
  TEMP_IN_USE_HIGH_WATER:   95197

declare a number := 1;
begin
  select max(a) into a from lru_tab;
  for i in 1..100000 loop  
    a := a+1;
    insert into lru_tab values(a, sysdate);
    commit;
  end loop;
end;
/
PL/SQL procedure successfully completed. Command> dssize;                                                                                                                                                        
  PERM_ALLOCATED_SIZE:      40960
  PERM_IN_USE_SIZE:         20582
  PERM_IN_USE_HIGH_WATER:   31652
  TEMP_ALLOCATED_SIZE:      131072
  TEMP_IN_USE_SIZE:         94548
  TEMP_IN_USE_HIGH_WATER:   95197

Command> select count(*) from lru_tab; < 200001 > 1 row found. Command> declare a number := 1; begin select max(a) into a from lru_tab; for i in 1..100000 loop a := a+1; insert into lru_tab values(a, sysdate); commit; end loop; end; / PL/SQL procedure successfully completed. Command> select count(*) from lru_tab;                                                                                                                                  < 300001 >
1 row found.
Command> dssize;

  PERM_ALLOCATED_SIZE:      40960
  PERM_IN_USE_SIZE:         26054
  PERM_IN_USE_HIGH_WATER:   31652
  TEMP_ALLOCATED_SIZE:      131072
  TEMP_IN_USE_SIZE:         94548
  TEMP_IN_USE_HIGH_WATER:   95197

$ tttracemon cachedb1_1122
Trace> level aging 3
Trace> flush
Trace> dump
0 records dumped
Trace> dump
23:28:28.939      31 AGING    1L  135C   2613P Entering sbAgingLRU(): curTime=1085, minAccessCounter=1039
23:28:28.939      32 AGING    1L  135C   2613P Exiting sbAgingLRU(): curTime=1085, minAccessCounter=1039, permRatio=0.236157, highMemThreshold=0.300000
23:29:28.979      33 AGING    1L  135C   2613P Entering sbAgingLRU(): curTime=1086, minAccessCounter=1039
23:29:28.979      34 AGING    2L  135C   2613P Entering sbAgingOneTable(): curTime=1086, ltblid= 1798064
23:29:28.984      35 AGING    2L  135C   2613P Exiting sbAgingOneTable(): curTime=1086, reason = 'no more qualified rows found', 0 deleted, 104800 remaining, tbl = ORACLE.LRU_TAB
23:29:28.994      36 AGING    1L  135C   2613P sbAgingLRU()(again): curTime=1086, minAccessCounter=1048
23:29:28.994      37 AGING    2L  135C   2613P sbAgingLRU(): skip table 1798064, table's min access=1085, curTime=1086, minAccessCounter=1048 23:29:29.004 38 AGING 1L 135C 2613P sbAgingLRU()(again): curTime=1086, minAccessCounter=1054 23:29:29.004 39 AGING 2L 135C 2613P sbAgingLRU(): skip table 1798064, table's min access=1085, curTime=1086, minAccessCounter=1054
23:29:29.014      40 AGING    1L  135C   2613P sbAgingLRU()(again): curTime=1086, minAccessCounter=1062
23:29:29.014      41 AGING    2L  135C   2613P sbAgingLRU(): skip table 1798064, table's min access=1085, curTime=1086, minAccessCounter=1062 23:29:29.025 42 AGING 1L 135C 2613P sbAgingLRU()(again): curTime=1086, minAccessCounter=1074 23:29:29.025 43 AGING 2L 135C 2613P sbAgingLRU(): skip table 1798064, table's min access=1085, curTime=1086, minAccessCounter=1074
23:29:29.025      44 AGING    1L  135C   2613P Exiting sbAgingLRU(): curTime=1086, minAccessCounter=1074
14 records dumped <- 最开始，说没有满足条件的数据可删，即使空间已经超过限制了
Trace> dump
23:37:40.751    4071 AGING    3L  135C   2613P curTime=1094, 0 deleted, 862 remaining, tbl = ORACLE.LRU_TAB
23:37:40.755    4072 AGING    3L  135C   2613P curTime=1094, 0 deleted, 762 remaining, tbl = ORACLE.LRU_TAB
23:37:40.762    4073 AGING    3L  135C   2613P curTime=1094, 0 deleted, 662 remaining, tbl = ORACLE.LRU_TAB
23:37:40.763    4074 AGING    3L  135C   2613P curTime=1094, 0 deleted, 562 remaining, tbl = ORACLE.LRU_TAB
23:37:40.769    4075 AGING    3L  135C   2613P curTime=1094, 0 deleted, 462 remaining, tbl = ORACLE.LRU_TAB
23:37:40.771    4076 AGING    3L  135C   2613P curTime=1094, 0 deleted, 362 remaining, tbl = ORACLE.LRU_TAB
23:37:40.772    4077 AGING    3L  135C   2613P curTime=1094, 0 deleted, 262 remaining, tbl = ORACLE.LRU_TAB
23:37:40.774    4078 AGING    3L  135C   2613P curTime=1094, 0 deleted, 162 remaining, tbl = ORACLE.LRU_TAB
23:37:40.776    4079 AGING    3L  135C   2613P curTime=1094, 0 deleted, 62 remaining, tbl = ORACLE.LRU_TAB
23:37:40.778    4080 AGING    3L  135C   2613P curTime=1094, 0 deleted, 0 remaining, tbl = ORACLE.LRU_TAB
23:37:40.778    4081 AGING    2L  135C   2613P Exiting sbAgingOneTable(): curTime=1094, reason = 'no more rows', 0 deleted, 0 remaining, tbl = ORACLE.LRU_TAB
23:37:40.778    4082 AGING    1L  135C   2613P Exiting sbAgingLRU(): curTime=1094, minAccessCounter=1089
509 records dumped <- 过一会一看，数据都删完了，就是Aging引起的

Trace> level aging 0

Command> dssize;

  PERM_ALLOCATED_SIZE:      40960
  PERM_IN_USE_SIZE:         9673
  PERM_IN_USE_HIGH_WATER:   39766
  TEMP_ALLOCATED_SIZE:      131072
  TEMP_IN_USE_SIZE:         93092
  TEMP_IN_USE_HIGH_WATER:   95197

Time-based aging

基于时间的Aging基于表中一个日期列，与当前时间比较。超过范围则删除。

所有的缓存组都可以定义基于时间的Aging

Command> create table tbaging (a int, ts timestamp)
       > AGING USE ts LIFETIME 1 MINUTES CYCLE 1 MINUTES ON;
 2993: Aging column cannot be nullable
The command failed.
Command> create table tbaging (a int, ts timestamp not null)
       > AGING USE ts LIFETIME 1 MINUTES CYCLE 1 MINUTES ON;

Command> desc tbaging;

Table ORACLE.TBAGING:
  Columns:
    A                               NUMBER (38)
    TS                              TIMESTAMP (6) NOT NULL
  Aging: Timestamp based uses column TS lifetime 1 minute cycle 1 minute on

1 table found.
(primary key columns are indicated with *)

Command> INSERT INTO tbaging VALUES (1, SYSDATE);
1 row inserted.
Command> INSERT INTO tbaging VALUES (2, SYSDATE);
1 row inserted.

Command> select * from tbaging;
< 1, 2016-04-13 23:50:51.000000 >
< 2, 2016-04-13 23:50:54.000000 >
2 rows found.

Command> sleep 120

Command> select * from tbaging;
0 rows found.

参考

• Cache User Guide: Chapter 4, Implementing aging in a cache group