tristaZero commented on a change in pull request #7977: URL: https://github.com/apache/shardingsphere/pull/7977#discussion_r514922920
########## File path: docs/document/content/features/sharding/principle/parse.en.md ########## @@ -31,8 +31,4 @@ To pursue good performance and quick achievement, the first generation of SQL pa The second generation of SQL parsing engine begins from 1.5.x version, ShardingSphere has adopted fully self-developed parsing engine ever since. Due to different purposes, ShardingSphere does not need to transform SQL into a totally abstract syntax tree or traverse twice through visitor. Using `half parsing` method, it only extracts the context required by data sharding, so the performance and compatibility of SQL parsing is further improved. -The third generation of SQL parsing engine begins from 3.0.x version. ShardingSphere tries to adopts ANTLR as the SQL parsing engine, and plans to replace the former parsing engine according to the order of `DDL -> TCL -> DAL –> DCL -> DML –>DQL`. It is still in the process of replacement and iteration. Hoping for a better compatibility with SQL, we use ANTLR in the parsing engine of ShardingSphere. Though complex expressions, recursions, sub-queries and other sentences are not focused by the sharding core of ShardingSphere, they can influence the friendliness to understand SQL. After being tested in actual cases, the performance of ANTLR is about 3-10 times slower than the self-developed parsing engine when parsing SQL. To compensate for this gap, ShardingSphere will put the SQL parsing tree of `PreparedStatement` in the cache. Therefore, `PreparedStatement` is recommended to be used as the pre-compile method to improve the performance. - -The overall structure of the third generation of SQL parser is shown in the following picture. - - +The third generation of SQL parsing engine begins from 3.0.x version. ShardingSphere tries to adopts ANTLR as the SQL parsing engine, and used Visit to obtain SQL Statement from AST. Starting from version 5.0.x, the architecture of the parsing engine has been refactored. At the same time, it is convenient to directly obtain the parsing results of the same SQL to improve parsing efficiency by putting the AST obtained from the first parsing into the cache. Therefore, we recommend that users adopt `PreparedStatement` this SQL pre-compilation method to improve performance. Currently, users can also use ShardingSphere's SQL parsing engine independently to obtain AST and SQL Statements for a variety of mainstream relational databases. In the future, the SQL parsing engine will continue to provide powerful functions such as SQL formatting and SQL templating. Review comment: and **used**(?) Visit ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
