WO2025066059A1 - Data maintenance method and device for database - Google Patents

Abstract

Disclosed in the present invention is a data maintenance method and device for a database. The method comprises: creating an automated database maintenance task, wherein the automated database maintenance task comprises at least one sub-task, and information comprised in each sub-task at least comprises: a table name, the number of keepdays KeepDays, the minimum number of keeprows KeepRowsMin, the maximum number of deleterows at a time DeleteRowsMax, and an expected next delete time NextDelTime; acquiring information comprised in a sub-task with a minimum expected next delete time in the automated database maintenance task; and when the expected next delete time NextDelTime comprised in the sub-task is less than or equal to a current system time DtNow, executing a data maintenance task on a corresponding data table in a database according to the information comprised in the sub-task, and during the execution of the data maintenance task, automatically deleting data in the data table KeepDays ago on the basis of a time field, and ensuring that at least KeepRowsMin rows of data are left in the data table, no more than DeleteRowsMax rows of data being deleted at a time. By means of the method of the present invention, database maintenance of a process control system can be completed in a full-automated mode, and the burden of manual maintenance is reduced.

Description

A method and device for maintaining database data Technical Field

The present invention relates to the technical field of database management, and in particular to a data maintenance method and device for a process control system database.

Background Art

The process control system is a management system that connects the upper and lower levels in the steel industry. It obtains master data from the upper-level manufacturing execution system, calculates production setting values, and sends them to the lower-level basic automation system for execution. During the production process, the process control system obtains the measured process data of the lower-level basic automation system, forms production results, and sends them to the upper-level manufacturing execution system.

In essence, a process control system is a system that involves data exchange, management, and display. It includes master data tables, performance data tables, production real-time process data tables, log tables, process parameter configuration tables, process parameter history tables, and so on. When the data in these tables increases, it may affect the query and writing efficiency of the program. Generally, real-time data needs to be saved for at least half a year, and material master data and performance data need to be saved for at least two years.

In order to ensure the stable and efficient operation of the system, maintenance personnel usually delete early historical data regularly. However, this operation not only increases the manual workload, but also may lead to the risk of misoperation.

Some process control systems use bat commands to periodically delete historical data, but this method has the following problems: 1. Deleting a large amount of data may cause the database to be locked for a short period of time, thus affecting the normal operation of the program. 2. If the unit is shut down for a long time, the data table may be completely cleared. 3. The deleted data cannot be viewed again.

Summary of the invention

The purpose of the present invention is to overcome at least one defect in the prior art and to provide a database According to maintenance methods and equipment.

To achieve the above object, the present invention provides a method for maintaining database data, comprising the following steps:

S1: Create a database automatic maintenance task, which includes at least one subtask. Each subtask contains at least the following information: table name, number of retention days KeepDays, minimum number of retained rows KeepRowsMin, maximum number of rows to be deleted at a time DeleteRowsMax, and expected next deletion time NextDelTime;

S2: Obtain information contained in the subtask with the smallest expected next deletion time in the database automatic maintenance task. When the expected next deletion time NextDelTime contained in the subtask is greater than the current system time DtNow, re-execute step S2; when the expected next deletion time NextDelTime contained in the subtask is less than or equal to the current system time DtNow, execute step S3;

S3: Perform data maintenance tasks on the corresponding data table in the database according to the information contained in the subtask. When performing the data maintenance task, automatically delete the data in the data table before KeepDays days according to the time field to ensure that at least KeepRowsMin rows of data remain in the data table, and no more than DeleteRowsMax rows of data can be deleted at a single time.

In some embodiments, establishing a database automatic maintenance task specifically includes: establishing a database automatic maintenance table, the fields of which include at least: table name, number of retention days KeepDays, minimum number of retained rows KeepRowsMin, maximum number of rows deleted at a time DeleteRowsMax, and expected next deletion time NextDelTime;

Each row of the database automatic maintenance table corresponds to a subtask.

In some embodiments, in step S2, when the expected next deletion time NextDelTime included in the subtask is greater than the current system time DtNow, wait for time T0 or T1, and then re-execute step S2.

In some embodiments, T0 is equal to the total number of seconds of NextDelTime minus DtNow and rounded up.

T1 is the set time.

In some embodiments, after each execution of the data maintenance task in S3, the expected next deletion time NextDelTime of the subtask is updated, the waiting time T1 is waited, and then step S2 is entered.

In some embodiments, before executing the data maintenance task, it also includes: determining whether there is a data table corresponding to the table name contained in the subtask in the database. If there is a corresponding data table in the database, the data maintenance task is executed on the data table; otherwise, the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then wait for T1 seconds to enter step S2, where T2 is greater than T1.

In some embodiments, there is one time field in the data table, and when executing the data maintenance task, the data in the data table before KeepDays days is automatically deleted according to the time field TimeFieldName;

or,

There are one or more time fields in the data table. The information contained in each subtask also includes a time field TimeFieldName. The time field TimeFieldName is one of the time fields in the data table. When executing the data maintenance task, the data in the data table before KeepDays days is automatically deleted according to the time field TimeFieldName.

In some embodiments, step S3 specifically includes:

S31: Obtain the total number of rows r1 in the data table whose time field TimeFieldName is less than deadlineLineTime, where deadlineLineTime is equal to the current system time DtNow minus the number of retention days KeepDays. If r1 is greater than 0, proceed to step S32;

S32: Get the total number of rows r2 in the data table, and get the minimum value delTarget among the three data r1, r2-KeepRowsMin, and DeleteRowsMax. If delTarget is greater than 0, go to step S33;

S33: obtaining delTime, including: searching the data table in ascending order according to the time field TimeFieldName, skipping the delTarget row, and obtaining the value of the time field TimeFieldName in the first row, namely delTime;

S34: Delete all rows in the data table whose time field TimeFieldName is less than delTime, and obtain the actual number of deleted rows delCnt. If delCnt is greater than or equal to DeleteRowsMax, update the NextDelTime of the subtask to the current system time DtNow plus T1 seconds, wait for T1 seconds and enter step S2. If delCnt is less than DeleteRowsMax, update the expected next deletion time NextDelTime of the subtask to the current system time DtNow plus T2 seconds, wait for T1 seconds and enter step S2, where T2 is greater than T1.

In some embodiments, after each execution of a data maintenance task, when it is found that the data maintenance task has not been completed (i.e., when r1 and r2-KeepRowsMin are both greater than DeleteRowsMax), the NextDelTime of the subtask is updated to the current system time DtNow plus T1 seconds, and step S2 is entered after waiting for T1 seconds; when it is found that the data maintenance task has been completed (i.e., when any one of r1 and r2-KeepRowsMin is less than or equal to DeleteRowsMax), the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and step S2 is entered after waiting for T1 seconds, and T2 is greater than T1.

In some embodiments, if r1 is equal to 0 in step S31, the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then step S2 is entered after waiting for T1 seconds;

and/or,

If delTarget is less than or equal to 0 in step S32, the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then the process goes to step S5 after waiting for T1 seconds.

In some embodiments, the information included in the subtask also includes: information for indicating whether to back up, and the following steps are included between step S33 and step S34: judging whether to back up according to the information included in the subtask, if so, executing the data backup step and then entering step S34, if not, skipping the data backup step and entering step S34;

The data backup step is performed, specifically including: obtaining all rows in the data table where the time field TimeFieldName is less than delTime, and performing a different database backup after generating backup data.

In some embodiments, performing the data backup step specifically includes: obtaining all rows in the data table where the time field TimeFieldName is less than delTime, and generating multiple rows of backup table data and storing them in the backup table;

The fields of the backup table include at least: a unique ID, the time of the original table, the name of the original table, a row of records in the original table, and the current time of the backup.

The present invention also discloses a database data maintenance device, comprising: a memory, a processor, and a database data maintenance program stored in the memory and executable on the processor, wherein the database data maintenance program is configured to implement the database data maintenance method as described above.

The present invention has at least the following beneficial effects:

1) The present invention can fully automatically complete the maintenance of the process control system database, reducing the burden of manual maintenance.

2) Before deleting the data table, the present invention first performs a different database backup, which can prevent accidental deletion of data on the one hand, and also provides a possibility for later data backtracking on the other hand.

3) The present invention performs current limiting operation during the data table deletion process, thereby avoiding table deadlock and ensuring the normal business logic operation of the process control system.

4) The data table of the present invention retains at least a certain amount of data to ensure that the HMI interface of the process control system The face will not be empty.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG. 1 is a flow chart of a method for maintaining data in a process control system database according to an embodiment of the present invention.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

In order to solve the problem that the long-term operation of the process control system causes the database to expand, thereby affecting the operation efficiency, the present invention proposes a method for maintaining historical data of the database. The method can ensure that the data table contains at least a certain number of rows, avoid deadlock by optimizing the deletion operation, and back up and save the deleted data to improve the operation stability of the database.

Referring to FIG. 1 , an embodiment of the present invention provides a data maintenance method for a process control system database, comprising the following steps:

S1: Create a database automatic maintenance task, which includes at least one subtask. Each subtask contains at least the following information: table name, number of retention days KeepDays, minimum number of retained rows KeepRowsMin, maximum number of rows to be deleted at a time DeleteRowsMax, and expected next deletion time NextDelTime;

S2: Get the information contained in the subtask with the smallest expected next deletion time in the database automatic maintenance task. When the expected next deletion time NextDelTime included in the subtask is greater than the current system time DtNow, wait for time T0 or T1, and then re-execute step S2; when the expected next deletion time NextDelTime included in the subtask is less than or equal to the current system time DtNow, execute step S3;

S3: Automatic data table maintenance, including executing data maintenance tasks on the data table corresponding to the table name contained in the subtask in the database according to the information contained in the subtask. When executing the data maintenance task, the data in the data table older than KeepDays days is automatically deleted according to the time field to ensure that at least KeepRowsMin rows of data remain in the data table, and no more than DeleteRowsMax rows of data are deleted at a single time.

In some embodiments, T0 is equal to the total number of seconds of NextDelTime minus DtNow and rounded up.

In some embodiments, after each execution of the data maintenance task in S3, the expected next deletion time NextDelTime of the subtask is updated, the waiting time T1 is waited, and then step S2 is entered.

T1 is the set time, which is generally a shorter time, such as 1 second.

The present invention can execute steps S2 and S3 regularly or periodically (such as at a time interval T1) to maintain the data in the database.

The present invention can be set so that the program starts running when the device is turned on, that is, starts to execute steps S2 and S3, and automatically ends running the program when the device is turned off.

In some embodiments, establishing a database automatic maintenance task specifically includes: establishing a database automatic maintenance table, the fields of the database automatic maintenance table include at least: table name, retention days KeepDays, minimum number of retained rows KeepRowsMin, maximum number of rows to be deleted at a time DeleteRowsMax, expected next deletion time NextDelTime; each row of the database automatic maintenance table corresponds to a subtask one by one.

In some embodiments, there is only one time field in the data table. When a data maintenance task is executed, data in the data table older than KeepDays days is automatically deleted according to the time field TimeFieldName.

In some other embodiments, the time field in the data table is one or more, and each subtask contains The information also includes a time field TimeFieldName, which is one of the time fields in the data table. When the data maintenance task is executed, the data in the data table before KeepDays days is automatically deleted according to the time field TimeFieldName.

In some embodiments, the fields for establishing a database automatic maintenance table include at least: table name, which is a string type and is the primary key; number of retention days, which is a single-precision floating point type; minimum number of rows to be retained, which is an integer type; maximum number of rows to be deleted, which is an integer type; time field, which is a string type; and expected next deletion time, which is a date and time type.

This database automatic maintenance table is generally built in the business database of the process control system, and of course it can also be built in an independent database or even a text file. In one embodiment, taking the MySQL database as an example, a database automatic maintenance table is established, the table name is cfg_db_maintenance, and the field details of the table are as follows:

Among them, one line contains the following:

TableName=mill_operation_log

KeepDays=30

KeepRowsMin=100

DeleteRowsMax=1000

TimeFieldName＝OperationTime

NextDelTime=2023-08-2920:28:03

It indicates that the program needs to automatically maintain the mill_operation_log table and automatically delete data older than 30 days based on the OperationTime time field, but it needs to ensure that there are at least 100 rows of data left in the mill_operation_log table and no more than 1,000 rows can be deleted at a time. The next time this maintenance task is executed is 2023-08-29 20:28:03.

In some embodiments, step S1 further includes establishing a backup table, the fields of which include: a primary key field, which ensures its uniqueness; the time of the original table, the type is date and time; the table name of the original table, the type is string type; a row of records in the original table, the type is text; the backup time, the type is date and time;

The primary key field can use a long integer as an auto-increment ID, or a string generated by a GUID. Preferably, the BIGINT generated by the SnowFlake component is used as the primary key field to ensure its increment and uniqueness. Compared with a GUID as a string, the SnowFlake component has higher read and write efficiency, and compared with an auto-increment ID, it does not expose the progress of business data.

It should be noted that the backup table should not be placed in the business database of the process control system, but should be stored in a third-party database. Taking a certain embodiment as an example, it is stored in the local SQLite database for easy backup and management. The name of this historical data backup table is HisDbBackup, and the field details of the table are as follows:

There is no doubt that RowJson will take up a lot of space in the future. It is the real location for the historical data backup of the process control system business database. This table design is very general and can back up various types of tables.

In some embodiments, T0 is equal to the total number of seconds of NextDelTime minus DtNow and rounded up.

In some embodiments, before executing the data maintenance task, it also includes: determining whether there is For the data table corresponding to the table name included in the subtask, if the data table corresponding to the table name included in the subtask exists in the database, the data maintenance task is performed on the data table; otherwise, the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then enter step S2 after waiting for T1 seconds, where T2 is greater than T1.

In some embodiments, step S3 specifically includes:

S31: Obtain the total number of rows r1 in the data table whose time field TimeFieldName is less than deadlineLineTime, where deadlineLineTime is equal to the current system time DtNow minus the number of retention days KeepDays. If r1 is greater than 0, proceed to step S32;

S32: Get the total number of rows r2 in the data table, and get the minimum value delTarget among the three data r1, r2-KeepRowsMin, and DeleteRowsMax. If delTarget is greater than 0, go to step S33;

S33: obtaining delTime, including: searching the data table in ascending order according to the time field TimeFieldName, skipping the delTarget row, and obtaining the value of the time field TimeFieldName in the first row, namely delTime;

S34: Delete all rows in the data table where the time field TimeFieldName is less than delTime.

In some embodiments, after deleting all rows in the data table whose time field TimeFieldName is less than delTime in step S34, the actual number of deleted rows delCnt is obtained. If delCnt is greater than or equal to DeleteRowsMax, the NextDelTime of the subtask is updated to the current system time DtNow plus T1 seconds, and step S2 is entered after waiting for T1 seconds. If delCnt is less than DeleteRowsMax, the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and step S2 is entered after waiting for T1 seconds, and T2 is greater than T1.

In some embodiments, the time field in the data table is deleted in step S34. After checking all the rows whose TimeFieldName is less than delTime, when it is found that the data maintenance task has not been completed (that is, when r1 and r2-KeepRowsMin are both greater than DeleteRowsMax), the NextDelTime of the subtask is updated to the current system time DtNow plus T1 seconds, and then enter step S2 after waiting for T1 seconds; when it is found that the data maintenance task has been completed (that is, when any one of r1, r2-KeepRowsMin is less than or equal to DeleteRowsMax), the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then enter step S2 after waiting for T1 seconds, where T2 is greater than T1.

In some embodiments, if r1 is equal to 0 in step S31, the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then step S2 is entered after waiting for T1 seconds.

In some embodiments, if delTarget is less than or equal to 0 in step S32, the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then step S5 is entered after waiting for T1 seconds.

In some embodiments, the information included in the subtask also includes: information for indicating whether to back up, and the following steps are included between step S33 and step S34: judging whether to back up according to the information included in the subtask, if so, executing the data backup step and then entering step S34, if not, skipping the data backup step and entering step S34;

The data backup step is performed, specifically including: obtaining all rows in the data table where the time field TimeFieldName is less than delTime, and performing a different database backup after generating backup data.

In some embodiments, performing the data backup step specifically includes: obtaining all rows in the data table where the time field TimeFieldName is less than delTime, and generating multiple rows of backup table data and storing them in the backup table;

The fields of the backup table include at least: unique ID, original table time, original table name, original table A line of records and backup current time.

In some embodiments, when the database automatic maintenance task is established in step S1 by establishing a database automatic maintenance table, step S2 specifically includes: obtaining the row Row in the automatic maintenance table with the smallest expected next deletion time, the row at least including the table name TableName, the number of retention days KeepDays, the minimum number of retained rows KeepRowsMin, the maximum number of deleted rows DeleteRowsMax, the time field TimeFieldName, and the expected next deletion time NextDelTime.

When NextDelTime is greater than the current system time DtNow, the process sleeps for T0 seconds and then re-executes step S2, where T0 represents the total number of seconds that have passed (NextDelTime-DtNow) and is rounded up to an integer.

When NextDelTime is less than or equal to the current system time DtNow, step S3 is executed;

Step S3 specifically includes:

Step S31, if the table TableName does not exist in the database, update the NextDelTime of Row to the current system time DtNow plus T2 seconds, and go to step S4, otherwise, execute step S32;

Step S32, get the total number of rows r1 in the table TableName whose time field TimeFieldName is less than deadlineLineTime, where deadlineLineTime is equal to DtNow minus KeepDays. If r1 is equal to 0, update the NextDelTime of Row to DtNow plus T2 seconds, and go to step S4. If r1 is greater than 0, go to step S33;

Step S33, get the total number of rows in table TableName, r2. Then get the minimum value delTarget among r1, r2-KeepRowsMin, DeleteRowsMax. If delTarget is less than or equal to 0, update the NextDelTime of the row Row to DtNow plus T2 seconds, and go to step S4. If delTarget is greater than 0, go to step S34.

Step S34, obtaining delTime, that is, searching in ascending order of TimeFieldName from the table TableName, skipping the delTarget row and selecting the first row whose TimeFieldName value is delTime.

Step S35, backup data: obtain all rows in the table TableName whose TimeFieldName is less than delTime, and generate multiple rows of backup table data, including the unique ID, the time of the original table (the time corresponding to the TimeFieldName of the row to be backed up in the original table), the table name of the original table, and the string after the entire JSON serialization of the current row, back up the current time, and store these data in the backup table.

Step S36, delete data: delete all rows in the table TableName where TimeFieldName is less than delTime, and return the actual number of deleted rows delCnt.

Step S37, if delCnt is greater than or equal to DeleteRowsMax, update the NextDelTime of Row to DtNow plus T1 seconds, and go to step S4, otherwise update the NextDelTime of Row to DtNow plus T2 seconds, and go to step S4.

Step S4, sleep for T1 seconds, and then enter step S2.

T1 is a shorter time, such as 1 second, and T2 is a longer time, such as 300 seconds. The specific meaning is that when it is found that the maintenance is completed, it will sleep for a longer time T2, and when it is found that the maintenance is not completed, it will sleep for a shorter time T1, and then continue the automatic maintenance.

It should be noted that for some tables, if the historical data is not important, you can choose not to back up. In this case, you need to add an additional field in the automatic maintenance table to indicate whether to back up. If no backup is needed, skip step S35.

Based on the same inventive concept, an embodiment of the present invention also discloses a database data maintenance device, including: a memory, a processor, and a database data maintenance program stored in the memory and executable on the processor, wherein the database data maintenance program is configured to implement the database data maintenance method as described above.

In some embodiments, the processor may be a central processing unit (CPU), a controller, a microcontroller, a microprocessor, or other data processing chip. The processor is generally used to control the overall operation of the electronic device. In this embodiment, the processor is used to run the storage The program code stored in the device or the program code for processing data, such as the data maintenance method of the database.

The memory includes at least one type of readable storage medium, and the readable storage medium includes flash memory, hard disk, multimedia card, card-type memory (for example, SD or DX memory, etc.), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic memory, disk, optical disk, etc. In some embodiments, the memory may be an internal storage unit of the electronic device, such as a hard disk or memory of the electronic device. In other embodiments, the memory may also be an external storage device of the electronic device, such as a plug-in hard disk, a smart memory card (SmartMedia Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (FlashCard), etc. equipped on the electronic device. Of course, the memory may also include both the internal storage unit of the electronic device and its external storage device. In this embodiment, the memory is generally used to store the operating method and various application software installed in the electronic device, such as the program code of the data maintenance method of the database, etc. In addition, the memory may also be used to temporarily store various types of data that have been output or are to be output.

Based on the same inventive concept, an embodiment of the present invention further discloses a storage medium, wherein the storage medium stores a data maintenance program for a database, and the data maintenance program for the database is used to implement the above-mentioned data maintenance method for the database when the processor executes the program.

Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage and optical storage, etc.) containing computer-usable program code.

The present invention is described with reference to flowcharts and/or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that the flowcharts and/or block diagrams can be implemented by computer program instructions. Each process and/or box in the figure, and the combination of the processes and/or boxes in the flowchart and/or block diagram. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate a device for implementing the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including an instruction device that implements the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

These computer program instructions may also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

Claims (10)

A method for maintaining database data, characterized in that it comprises the following steps: S1: Create a database automatic maintenance task, which includes at least one subtask. Each subtask contains at least the following information: table name, number of retention days KeepDays, minimum number of retained rows KeepRowsMin, maximum number of rows to be deleted at a time DeleteRowsMax, and expected next deletion time NextDelTime; S2: Obtain information contained in the subtask with the smallest expected next deletion time in the database automatic maintenance task. When the expected next deletion time NextDelTime contained in the subtask is greater than the current system time DtNow, re-execute step S2; when the expected next deletion time NextDelTime contained in the subtask is less than or equal to the current system time DtNow, execute step S3; S3: Perform data maintenance tasks on the corresponding data table in the database according to the information contained in the subtask. When performing the data maintenance task, automatically delete the data in the data table before KeepDays days according to the time field to ensure that at least KeepRowsMin rows of data remain in the data table, and no more than DeleteRowsMax rows of data can be deleted at a single time. The data maintenance method of a database as claimed in claim 1 is characterized in that: establishing a database automatic maintenance task specifically includes: establishing a database automatic maintenance table, the fields of which include at least: table name, number of retention days KeepDays, minimum number of retained rows KeepRowsMin, maximum number of rows deleted at a time DeleteRowsMax, and expected next deletion time NextDelTime; Each row of the database automatic maintenance table corresponds to a subtask. The method for maintaining database data as claimed in claim 1, characterized in that: in step S2, when the expected next deletion time NextDelTime contained in the subtask is greater than the current system time DtNow, wait for time T0 or T1, and then re-execute step S2; T0 is equal to the total number of seconds of NextDelTime minus DtNow and rounded upward, and T1 is the set time; After each data maintenance task is executed in S3, the expected next deletion time NextDelTime of the subtask is updated, the waiting time T1 is waited, and then step S2 is entered. The data maintenance method for a database as described in claim 1 is characterized in that: before executing the data maintenance task, it also includes: judging whether there is a data table corresponding to the table name contained in the subtask in the database, if the corresponding data table exists in the database, executing the data maintenance task on the data table, otherwise, updating the expected next deletion time NextDelTime of the subtask to the current system time DtNow plus T2 seconds, and waiting for T1 seconds before entering step S2, T2 is greater than T1. The method for maintaining database data according to claim 1, wherein: There is one time field in the data table. When executing the data maintenance task, the data in the data table before KeepDays days is automatically deleted according to the time field TimeFieldName. or, There are one or more time fields in the data table. The information contained in each subtask also includes a time field TimeFieldName. The time field TimeFieldName is one of the time fields in the data table. When executing the data maintenance task, the data in the data table before KeepDays days is automatically deleted according to the time field TimeFieldName. The method for maintaining database data as claimed in claim 5, characterized in that step S 3 specifically comprises: S31: Obtain the total number of rows r1 in the data table whose time field TimeFieldName is less than deadlineLineTime, where deadlineLineTime is equal to the current system time DtNow minus the number of retention days KeepDays. If r1 is greater than 0, proceed to step S32; S32: Get the total number of rows r2 in the data table, and get the minimum value delTarget among the three data r1, r2-KeepRowsMin, and DeleteRowsMax. If delTarget is greater than 0, go to step S33; S33: obtaining delTime, including: searching the data table in ascending order according to the time field TimeFieldName, skipping the delTarget row, and obtaining the value of the time field TimeFieldName in the first row, namely delTime; S34: Delete all rows in the data table whose time field TimeFieldName is less than delTime, and obtain the actual number of deleted rows delCnt. If delCnt is greater than or equal to DeleteRowsMax, update the NextDelTime of the subtask to the current system time DtNow plus T1 seconds, wait for T1 seconds and enter step S2. If delCnt is less than DeleteRowsMax, update the expected next deletion time NextDelTime of the subtask to the current system time DtNow plus T2 seconds, wait for T1 seconds and enter step S2, where T2 is greater than T1. The method for maintaining database data according to claim 6, characterized in that: if r1 is equal to 0 in step S31, then the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then step S2 is entered after waiting for T1 seconds; and/or, If delTarget is less than or equal to 0 in step S32, the expected next deletion time NextDelTime of the subtask is updated to the current system time DtNow plus T2 seconds, and then the process goes to step S5 after waiting for T1 seconds. The method for maintaining database data according to claim 6, characterized in that: the information contained in the subtask also includes: information for indicating whether to back up, and the following steps are further included between step S33 and step S34: judging whether to back up according to the information contained in the subtask, if so, executing the data backup step and then entering step S34, if not, skipping the data backup step and entering step S34; The data backup step is performed, specifically including: obtaining all rows in the data table where the time field TimeFieldName is less than delTime, and performing a different database backup after generating backup data. The method for maintaining database data according to claim 8, characterized in that: executing the data backup step specifically comprises: obtaining all rows in the data table where the time field TimeFieldName is less than delTime, and generating multiple rows of backup table data and storing them in the backup table; The fields of the backup table include at least: a unique ID, the time of the original table, the name of the original table, a row of records in the original table, and the current time of the backup. A database data maintenance device, characterized in that it includes: a memory, a processor, and a database data maintenance program stored in the memory and executable on the processor, wherein the database data maintenance program is configured to implement the database data maintenance method as described in any one of claims 1 to 9.