redis两种持久化方式的区别是什么

redis提供两种方式进行持久化，一种是RDB持久化（原理是将Reids在内存中的数据库记录定时dump到磁盘上的RDB持久化），另外一种是AOF（append only file）持久化（原理是将Reids的操作日志以追加的方式写入文件）。

RDB持久化是指在指定的时间间隔内将内存中的数据集快照写入磁盘，实际操作过程是fork一个子进程，先将数据集写入临时文件，写入成功后，再替换之前的文件，用二进制压缩存储。（推荐学习：Redis视频教程）

AOF持久化以日志的形式记录服务器所处理的每一个写、删除操作，查询操作不会记录，以文本的方式记录，可以打开文件看到详细的操作记录。

RDB持久化和AOF持久化的区别：

1、存储数据

RDB持久化保存键空间的所有键值对(包括过期字典中的数据),并以二进制形式保存，符合rdb文件规范，根据不同数据类型会有不同处理。

AOF持久化保存redis服务器所执行的所有写命令来记录数据库状态,在写入之前命令存储在aof_buf缓冲区。

2、持久化时间选择

RDB持久化通过conf的save选项设置持久化行为(单位时间内的修改次数)。

AOF持久化通过conf的appendfsync选项设置持久化行为(单位时间内的修改次数)。

3、数据还原

RDB持久化：服务器载入rdb文件，阻塞线程，在载入完成之前不接受任何命令。

AOF持久化：服务器创建不带网络连接的伪客户端，读取aof文件中的所有命令并执行(redis服务开启aof持久化在服务器启动时会选择aof文件恢复数据库状态)

4、过期键

RDB持久化在写入或读取时会忽略过期键

AOF持久化不会忽略过期键，在键被惰性删除或定期删除时向aof文件追加一条删除命令

5、文件大小

RDB持久化随着存储数据量的变化而变化(根据不同数据类型有不同的数据压缩优化)

AOF持久化随着执行命令的增加而增加(通过aof重写进行优化)

更多redis相关技术知识，请访问Redis使用入门教程栏目学习！

首先

不规则动词过去式和过去分词

A. 原型,过去式,和过去分词 完全不同

drink---drank----drunk

ring----rang-----rung

swim----swam----swum

sing----sang----sung

sink----sank----sunk

blow----blew----blown

grow----grew----grown

know---knew---known

fly ----flew----flown

take----took----taken

shake----shook----shaken

drive----drove----driven

write---wrote---written

rise---rose---risen

ride----rode----ridden

speak----spoke----spoken

steal----stole----stolen

break----broke----broken

wake----woke----woken

freeze----froze----frozen

forget----forgot----forgotten

choose----chose----chosen

draw----drew----drawn

eat----ate----eaten

fall----fell----fallen

give----gave----given

hide----hid----hidden

see----saw----seen

do----did----done

B. 过去式与过去分词完全相同

bright----brought----brought

think----thought----thought

fight----fought----fought

buy----bought----bought

catch----caught----caught

sell----sold----sold

tell----told----told

say----said----said

pay----paid----paid

send----sent----sent

lend----lent----lent

spend----spent----spent

burn----burnt----burnt

learn----learnt----learnt

mean----meant----meant

feel----felt----felt

smell----smelt----smelt

sleep----slept----slept

sweep---slept----slept

leave----left----left

build----built----built

lose----lost----lost

get----got----got

meet----met----met

sit----sat----sat

shoot----shot----shot

lead----led----led

spit----spat----spat

have----had----had

hold----held----held

make----made----made

stand----stood---stood

hear----heard----heard

find----found----found

dig----dug----dug

shine----shone----shone

understand----understood--understood win----won----won

C.原型与过去分词相同

come----came----come

run----ran----run

become----became----become

D.原形与过去式和过去分词完全相同

cast----cast----cast

cut----cut----cut

put----put----put

let----let----let

set----set----set

hit----hit----hit

shut----shut----shut

hang----hung----hung 吊,挂 lie---lied---lied 说谎

lie---lay---lain 躺下,位于,平放

hanged----hanged 处绞刑

lay---laid---laid 置放.

容词比较级和最高级的形式

http://ting.24en.com/flash/5/2006-04-19/5091.html

这个网页上有相关的FLASH可以看.

一、形容词比较级和最高级的构成

形容词的比较级和最高级变化形式规则如下

构 成 法 原 级 比 较 级 最 高 级

① 一般单音节词末尾加?er 和 ?est strong stronger strongest

② 单音节词如果以?e结尾,只加?r 和?st strange stranger strangest

③ 闭音节单音节词如末尾只有 一个辅音字母,

须先双写这个辅音字母,再加?er和?est sad

big

hot sadder

bigger

hotter saddest

biggest

hottest

④ 少数以?y,?er(或?ure),?ow,?ble结尾的双音节词,

末尾加?er和?est(以?y结尾的词,如?y前是辅音字母,

把y变成i,再加?er和?est,以?e结尾的词仍

只加?r和?st) angry

clever

narrow

noble angrier

cleverer

narrower

nobler angrest

cleverest

narrowest

noblest

⑤ 其他双音节和多音节词都在前面加单词more和most different more

different most

different

1) The most high 〔A〕 mountain in 〔B〕 the world is Mount Everest, which is situated 〔C〕 in Nepal and is

twenty?nine thousand one hundred and fourty one feet high 〔D〕 .

2) This house is spaciouser 〔A〕 than that 〔B〕 white 〔C〕 one I bought in Rapid City, South Dakota 〔D〕 last year.

3) Research in the social 〔A〕 sciences often proves difficulter 〔B〕 than similar 〔C〕 work in the physical 〔D〕 sciences.

二、形容词比较级或最高级的特殊形式：

1. 三个或三个以上音节的形容词只能加more和most

只能说 more beautiful而不能说beautifuller; 只能说the most beautiful而不能说beautifullest.

但是,以形容前缀?un结尾的三音节形容词不适合上述情况,如unhappy,untidy,我们可以说：unhappier→unhappiest, untidier→untidiest

2. 由?ING分词和?ED分词演变过来的形容词(包括不规则动词如know→known)只能加more或most来表示它们的比较级和最高级

more(most) striking, more(most) interesting, more(most) wounded, more(most)worn等.

4) The drawings 〔A〕 of the old masters 〔B〕 are among the treasuredest 〔C〕 works in museums 〔D〕 .

3. 英语里有些形容词由于其词义而不可能有比较级形式

absolute fatal main right universal

chief final naked simulta- utter

entire foremost perfect neous vital

eternal?inevitable?possible?sufficient?whole?

excellent infinite primary supreme wooden

三、不规则形容词的比较级和最高级形式

good

well? better?best

bad

ill?worse?worst

many

much? more?most

little

few? less?least

far? farther?farthest

further?furthest

5) African elephants are larger, fiercer, and difficulter 〔A〕 to tame 〔B〕 than 〔C〕 Asian elephants 〔D〕 .

6) Sarah Hale became 〔A〕 one of the famousest 〔B〕 magazine 〔C〕 editors in the United States during 〔D〕 the 1800’s.

7) Of all 〔A〕 the Native American tribes 〔B〕 , the Shawnee Indians were 〔C〕 a most 〔D〕 transient.

四、例题解析

1) A错.应将“most high”改为highest.这是在考形容词比较级的构成形式.

2) A错.改为more spacious.

3) B错. 改为more difficult.

4) C错. treasured 在本句中是?ED分词(动词treasure ＋ed)作形容词使用,是“宝贵的、珍贵的”意思,修饰名词 works(作品),其最高级形式应用 the most treasured.

5) A错,改为more difficult.

6) B错.改为“the most famous”,因为famous(著名的)是双音节,其最高级变化应在前面加“the most”.

7) D错.应改为“the most”,因为此处表示的是最高级,“the most transient”意为“(延续时间)最短暂的”.

第二节 副词比较级和最高级的形式

副词比较级和最高级的变化形式与形容词基本上一样

一般 副词

hard→harder →hardest

fast→faster →fastest

late→later →latest

early→earlier →earliest

特殊 副词

well →better →best

much →more →most

badly →worse →worst

little →less →least 但是,开放类副词即以后缀?ly结尾的副词不能像形容词那样加?er或?est,如

quickly →more quickly →most quickly quietly →more quietly →most quietly

〔注〕： early中的?ly不是后缀,故可以把?y变?i再加?er和?est

第三节 形容词与副词比较级和最高级的基本用法

一、原级比较的基本用法

1. 原级比较由“as＋形容词或副词(或再加名词或短语)＋as ”构成“原级相同”比较句,表示两者比较；其否定式,即“程度不及”比较句型为“not so(as) ＋形容词或副词＋as”,而且as…as结构前可用just, almost, nearly, quite等表示程度的词修饰

1) Walking briskly for thirty minutes will burn as many calories as .

〔A〕 to run for fifteen minutes

〔B〕 running for fifteen minutes

〔C〕 you run for fifteen minutes

〔D〕 fifteen?minute walking

2) The gorilla(大猩猩), while 〔A〕 not quite as curious than 〔B〕 the chimpanzee(黑猩猩), shows more persistence 〔C〕 and memory retention(记忆力) in solving 〔D〕 a problem.

3) Alaska is twice 〔A〕 as larger 〔B〕 as 〔C〕 the next largest 〔D〕 state, Texas.

2. “as (so)＋名词＋as＋名词”进行名词比较,这时一般情况下有一个表示原级的比较词,但如果第一名词前出现了形容词修饰该词或出现副词修饰谓语,应当用so而不用as

4) Thomas Jefferson’s achievements as an architect rival his contributions a politician.

〔A〕 such

〔B〕 more

〔C〕 as

〔D〕 than

5) I should say Henry is not much a writer as a reporter. (88年考题)

〔A〕 that

〔B〕 so

〔C〕 this

〔D〕 as

二、比较级

1. 比较级由“形容词(副词)比较级＋than＋…,”构成表示在两者中间一方比另一方“更加…”.连词than后可接句子,也可接名词、代词、名词短语、介词短语、动词、动词不定式、?ING结构和?ED结构,有时也可省去than.

6) Natural mica(云母) of 〔A〕 a superior 〔B〕 quality is cheapest 〔C〕 to obtain than synthetic 〔D〕 mica.

7) She is older than .

〔A〕 any other girl in the group

〔B〕 any girl in the group

〔C〕 all girls in the group

〔D〕 you and me as well as the group

8) Josephine McCrackin joined 〔A〕 the “Santa Cruz Sentinel” in 1905 and, until her death fifteen years late 〔B〕 , remained 〔C〕 active in journalistic 〔D〕 work.

2. 注意than前后两项相比较的人或事物要一致

9) The purpose of the research had a more important meaning for them than .

〔A〕 ours

〔B〕 with us

〔C〕 for ours it had

〔D〕 it did for us

10) Sound travels air.

〔A〕 faster through water than through 〔B〕 faster than through water and

〔C〕 through water faster and〔D〕 where it is faster through water than through

11) Gerbrand von den Feckhout, one of Rembrand’s pupils, followed 〔A〕 the style of his teacher so implicitly that 〔B〕 his paintings 〔C〕 are sometimes confused with his master 〔D〕 .

三、最高级

1. 最高级用于三者以上比较,形容词的结构形式是“定冠词＋形容词最高级＋名词＋表示范围的短语或从句”(如all, of all, of the tree, in the world, that has ever taken place等)

12) The more 〔A〕 fearsome of all the 〔B〕 animals in 〔C〕 the Western 〔D〕 Hemisphere is the grizzly bear.

13) Of all economic 〔A〕 problems, inflation continues to be 〔B〕 a 〔C〕 most significant in its daily impact on 〔D〕 people and business.

14) , the most familiar to general public is the criminal jurisdiction.

〔A〕 All the activities

〔B〕 The activities

〔C〕 Of all the activities

〔D〕 It is the activities

2. 副词的最高级与形容词最高级的区别在于最高级前没有定冠词the

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