TimesTen 应用层数据库缓存学习：6. Aging策略
2016-04-14 16:52
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declare a number := 1;
begin
select max(a) into :a from lru_tab;
a := a+1;
insert into lru_tab values(a, sysdate);
end;
/
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.
LRU aging:
LRU aging策略设置
强制启动Aging（无论定义了Aging的表设置Aging为on还是off）
Aging的开通，开启，关闭
Aging监控
可以用
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.
所有的缓存组都可以定义基于时间的Aging
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
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