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How was the middle table destroyed?

2022-07-05 16:31:00 【CSDN cloud computing】

author | Don't eat tomatoes

source | CSDN Blog

Generation of intermediate table

The intermediate table is a data table in the database that stores intermediate calculation results , It is often a summary table established in the database for faster or more convenient front-end query and statistics , Because it is an intermediate result processed from raw data , Therefore, it is called intermediate table .

In some large institutions , The number of intermediate watches accumulated over the years is as high as tens of thousands , It causes a lot of trouble to the system and use .

Intermediate tables will occupy a lot of database storage space, resulting in insufficient database capacity , Facing expansion pressure . Database space is often expensive , The cost of expansion is very high , And database expansion is often limited , It is not a good way to store intermediate tables at high cost . meanwhile , Too many intermediate tables will also cause database performance problems , Intermediate tables do not exist in isolation , From the original data to the intermediate table, it needs a series of operations, which consumes database computing resources , And the frequency of processing intermediate tables is sometimes very high , A lot of resources of the database are consumed in the generation of intermediate tables , Serious cases will cause slow database queries 、 Slow trading and other issues .

Why are there so many intermediate tables ？ The main reasons are as follows .

1、 One step cannot be calculated

The original data table in the database needs complex calculation , Can be shown on the report . One SQL It is difficult to achieve such complex calculations . There should be multiple consecutive SQL Realization , The former generates an intermediate table for the latter SQL Use .

2、 The waiting time for real-time calculation is too long

Because of the large amount of data or complex calculation , Report users wait too long . So run batch tasks every night , Calculate the data and store it in the intermediate table . Report users will query much faster based on the intermediate table .

3、 Diverse data sources participate in the calculation

From file 、NOSQL、Web service And other external data , It doesn't have much computing power , Need to use the computing power of the database , Especially when you want to perform mixed calculation with the data in the database , The traditional method can only import the database to form an intermediate table .

4、 The middle table is difficult to delete

Because the database usually adopts a flat structure that lacks hierarchy , Once created, the intermediate table may be used by multiple queries , Deleting may affect other queries . It's even hard to figure out which programs use an intermediate table , Not to mention deleting , It's not that I don't want to delete , But dare not delete . Accumulate over a long period , It's not surprising that there are tens of thousands of middle watches .

that , Why save intermediate data into the database to form an intermediate table ？ Careful observation of the direct cause of the middle table can be seen , The main purpose of saving to the database is to continue to rely on the computing power of the database . Intermediate data will be further calculated when used , Sometimes the calculation is complicated , At present, there are only databases （SQL） Have more convenient computing ability . Although data storage forms such as files also have advantages （ Such as IO High performance 、 Compressible 、 Easy to parallel ）, But the document has no computing power , If the calculation is hard coded in the application based on the file , Far from it SQL convenient . In order to make further use of the computing power of the database is the fundamental reason for the generation of intermediate tables .

Intermediate data is necessary in a sense , But just to obtain further computing power, it will occupy a lot of database resources , Obviously, it is not an ideal solution . If the file has the same ability as the database , Storing the intermediate table in the file system outside the database can solve various problems of the intermediate table in the database , The database can also be freed （ alleviate excessive burden ）.

Open source SPL It can be achieved .

SPL Is an open source structured data computing engine , Data processing can be directly based on files , Make the file also have computing power .SPL Database independent , It provides professional structured data objects and rich operation class libraries on them , Have complete computing power , At the same time, it supports process control , It is also convenient to realize complex calculation , It can completely replace the database to complete the intermediate table generation and subsequent data processing tasks .

Document calculation

SPL Can be based on Csv、Excel Wait for documents to calculate , You can also calculate JSON/XML And so on , Easy to read and use . such , You can store intermediate table data into such files , Reuse SPL Processing . Here are some general operations ：

	A	B
1	=T("/data/scores.txt")
2	=A1.select(CLASS==10)	Filter
3	=A1.groups(CLASS;min(English),max(Chinese),sum(Math))	Group summary
4	=A1.sort(CLASS:-1)	Sort
5	=T("/data/students.txt").keys(SID)
6	=A1.join(STUID,A5,SNAME)	relation
7	=A6.derive(English+ Chinese+ Math:TOTLE)	Append column

In addition to the original SPL grammar ,SPL It also provides quite SQL92 The standard SQL Support , For familiar with using SQL People can use it directly SQL Query file .

$select * from d:/Orders.csv where Client in ('TAS','KBRO','PNS')

More complicated with All support ：

$select t.Client, t.s, ct.Name, ct.address from
(select Client ,sum(amount) s from d:/Orders.csv group by Client) t
left join ClientTable ct on t.Client=ct.Client

SPL Processing JSON/XML And so on （ file ） It also has advantages , Such as ： According to the employee order information （json） Complete the calculation .

	A
1	=json(file("/data/EO.json").read())
2	=A1.conj(Orders)
3	=A2.select(Amount>1000 && Amount<=3000 && [email protected](Client,"s"))	filter
4	=A2.groups(year(OrderDate);sum(Amount))	Group summary
5	=A1.new(Name,Gender,Dept,Orders.OrderID,Orders.Client,Orders.Client,Orders.SellerId,Orders.Amount,Orders.OrderDate)	Associated calculation

You can see , Relative to others JSON library （ Such as JsonPath）SPL The implementation of is simpler .

Again , Use SQL You can also check JSON data ：

$select * from {json(file("/data/EO.json").read())}
where Amount&gt;=100 and Client like 'bro' or OrderDate is null

SPL Agile syntax and process computing are also very suitable for complex computing , For example, based on stock records （txt） Calculate the longest consecutive days of a stock It can be written like this ：

	A
1	=T("/data/stock.txt")
2	[email protected](price<price[-1]).max(~.len())-1

Another example , According to the user login record （csv） List the last login interval of each user ：

	A
1	=T(“/data/ulogin.csv”)
2	=A1.groups(uid;top(2,-logtime))	Last 2 Login records
3	=A2.new(uid,#2(1).logtime-#2(2).logtime:interval)	Calculation interval

Such calculations are even based on database usage SQL It's also hard to write ,SPL It is very convenient to realize .

With SPL Out of Library computing support , Originally, various problems caused by the intermediate table of the database can be effectively solved . File storage no longer takes up database storage space , The pressure of database expansion decreases , The database is more convenient to manage ; Out of Library computing no longer occupies database computing resources , Database load reduction can better serve other businesses .

High performance file format

Although text is a very common form of data storage , It has the advantages of versatility and readability , however , The performance of text is very poor ！ It is difficult to achieve high performance based on text .

Text characters cannot be calculated directly , Need to convert to an integer 、 The set of real Numbers 、 date 、 String and other memory data types can be further processed , Text parsing is a very complex task ,CPU Time consuming . In general , The main time of external memory data access is the reading of the hard disk itself , However, the performance bottleneck of text files often occurs in CPU link . Because of the complexity of parsing ,CPU It is likely to take more time than the hard disk （ Especially when using high-performance solid-state drives ）. Text is usually not used when high-performance processing of large amounts of data is required .

SPL Provides two high-performance data storage formats , Set files and group tables . The set file is SPL Binary data format provided , Compression technology is adopted （ Smaller footprint and faster reading ）, Stored data type （ There is no need to parse the data type, and reading is faster ）, It also supports the multiplication and segmentation mechanism of appendable data , It is easy to realize parallel computing by using segmentation strategy , Further improve computing performance .

Group table is SPL Provide inventory 、 File storage format of indexing mechanism , The number of columns involved in the calculation （ Field ） When there is less inventory, it will have great advantages . The group table supports column storage , Realized minmax Index outside , It also supports the multiplication and segmentation mechanism , In this way, we can not only enjoy the advantages of inventory , It is also easier to improve parallel computing performance .

SPL Storage is very convenient , Basically consistent with the use of text , For example, read the set file and calculate ：

	A	B
1	=T("/data/scores.btx")	Read in set file
2	=A1.select(CLASS==10)	Filter
3	=A1.groups(CLASS;min(English),max(Chinese),sum(Math))	Group summary

If the amount of data is large , It also supports cursor batch reading and multiple CPU Parallel computing ：

=file("/data/scores.btx")[email protected]()

When using files as data storage , No matter what format the original data is , Finally, they must at least be converted into binary （ Such as set file ） Format , In this way, it will have more advantages in terms of space occupation and computing performance .

Manageability

After the intermediate table is transferred outside the library and stored by file , In addition to reducing the burden on the database , The intermediate table outside the library itself also has strong manageability . Files can be stored through the tree directory of the system , Easy to use and manage . Different systems 、 The intermediate tables used by different modules are stored in different directories very clearly , There will be no cross references , In this way, there will be no tight coupling problem before each system or module caused by the previous confusion of the use of intermediate tables in the database . If the corresponding function module is offline, you can safely delete the corresponding intermediate table data without worrying about the impact on other programs .

Multi data source support

In addition to file data sources ,SPL It also supports dozens of other data sources , You can not only connect and access , It can also complete mixed calculation .

After the intermediate table is stored in files, cross source calculation is involved in the full query with the real-time data in the database , Use SPL Complete such T+0 Inquiry is very convenient .

	A
1	=cold=file(“/data/orders.ctx”).open().cursor(area,customer,amount)	/ Cold data from file system （SPL High performance storage ） To take , Yesterday's and previous data
2	=hot=db.cursor(“select area,customer,amount from orders where odate>=?”,date(now()))
3	=[cold,hot].conjx()	/ Heat data is taken from the production Library , Today's data
4	=A3.groups(area,customer;sum(amout):amout)	/ Hybrid computing implementation T+0

Integration

SPL Provides standards JDBC and ODBC Call for interface supply . Specially , about Java Applications can put SPL Integrated into the application as an embedded engine , Make the application itself have intermediate （ data ） Table processing capacity .

JDBC call SPL Code example ：

…
Class.forName("com.esproc.jdbc.InternalDriver");
Connection conn =DriverManager.getConnection("jdbc:esproc:local://");
Statement st = connection.();
CallableStatement st = conn.prepareCall("{call splscript(?, ?)}");
st.setObject(1, 3000);
st.setObject(2, 5000);
ResultSet result=st.execute();
…

SPL It's the interpretation of execution , Natural support for hot switching . be based on SPL Data calculation logic writing 、 There is no need to restart for modification and operation and maintenance , In real time , Development, operation and maintenance are also more convenient .

With the ability to calculate outside the Library SPL, Move the intermediate table to the file system , It can help the database eliminate tens of thousands of intermediate tables , While reducing the burden on the database , Get more flexibility 、 Faster performance and stronger scalability .