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This article mainly explains "how to troubleshoot and solve midline problems in python programming projects". The explanation in this article is simple and clear and easy to learn and understand. Please follow the editor's train of thought to study and learn "how to troubleshoot and solve online problems in python programming projects".

Problem description

Recently, due to the business needs of the company, the product has designed a set of business system, which is said to be used by many internal and external personnel. getting the system shows that our R & D department is desperately working overtime to catch up with time, and finally put the system online after two months.

At the beginning, few people used it, and there was no problem, and it felt that the system was still very stable. as more and more people used it later, some inexplicable problems began to appear in the system. among them, some business information always reported errors when updating, and it was found that the update failed because the table records were locked.

After finding the error problem, we began to go through the log over and over again, analyzing and finding out what caused the table record to be locked. Finally, it is found that in the status field of this table, multiple interface methods are updated at the same time, and often operate at the same time. That is, there are multiple sessions in the database that operate on the same row of records in the same table at the same time, resulting in table records being locked.

Analysis of problems

If we locate the problem, how can we solve it? Here we first learn about two nouns:

Pessimistic lock (Pessimistic Lock): the simple explanation is that it is very pessimistic. Every time you go to get the data, you think that someone else will change it, so it will be locked every time you modify the data, so that others will wait until it can get the lock if they want to change the data.

Optimistic lock (Optimistic Lock): on the contrary, it is very optimistic. Every time you modify the data, you think that someone else will not change it, so it will not be locked, but when you submit the update, you will determine whether someone else has updated the data during this period. Optimistic locks are suitable for application scenarios with more reads and less writes, which can improve throughput.

The problem can be solved in these two ways, but which one is better, let's briefly analyze it:

Pessimistic locking is achieved through "select... for update", which is to lock the record before updating the table, and then execute the update statement below. However, this method is a little too heavy, after all, locking still requires a lot of time cost, does not meet the needs of the business, directly pass off.

Optimistic locking is relatively lightweight, and its main implementation is by adding an additional record version field to the table, such as version. Then every time the query record is to be updated, version=? should be added after the where, so that when you query and get the version, if other sessions update this field, the version will be different from what you have now, which will invalidate your update this time. You need to re-get the latest version and execute the update statement again.

Problem solving

Well, after the above analysis, we have a relatively clear solution, and the rest is the code:

/ * optimistic lock update * @ param id * @ return * / public boolean update (int id) {int cnt = 0; while (cnt = = 0) {USER user = query ("SELECT * FROM table_user WHERE id = # {id}", id) Cnt = update ("UPDATE table_user SET version=version + 1, status = 2 WHERE id=# {id} AND version=# {version}", id, user.version ()); if (cnt > 0) {/ / return updated return true;}} return false Thank you for your reading, the above is the content of "how to troubleshoot and solve online problems in python programming projects". After the study of this article, I believe you have a deeper understanding of how to troubleshoot and solve online problems in python programming projects, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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