IndexWriter writer = new IndexWriter(FSDirectory.open(INDEX_DIR), new StandardAnalyzer(Version.LUCENE_CURRENT), true, IndexWriter.MaxFieldLength.LIMITED); writer.setUseCompoundFile(false); indexDocs(writer, docDir); writer.flush(); //flush
IndexWriter writer = new IndexWriter(FSDirectory.open(INDEX_DIR), new StandardAnalyzer(Version.LUCENE_CURRENT), true, IndexWriter.MaxFieldLength.LIMITED);
writer.setUseCompoundFile(false);
indexDocs(writer, docDir);
writer.flush();
//flush生成segment "_0",并且flush函数中,flushDocStores设为false,也即下个段将同本段共享域和词向量信息,这时DocumentsWriter中的docStoreSegment= "_0"。
indexDocs(writer, docDir);
writer.commit();
//commit生成segment "_1",由于上次flushDocStores设为false,于是段"_1"的域以及词向量信息是保存在"_0"中的,在这个时刻,段"_1"并不生成自己的"_1.fdx"和"_1.fdt"。然而在commit函数中,flushDocStores设为true,也即下个段将单独使用新的段来存储域和词向量信息。然而这时,DocumentsWriter中的docStoreSegment= "_1",也即当段"_2"存储其域和词向量信息的时候,是存在"_1.fdx"和"_1.fdt"中的,而段"_1"的域和词向量信息却是存在"_0.fdt"和"_0.fdx"中的,这一点非常令人困惑。 如图writer.commit的时候,_1.fdt和_1.fdx并没有形成。
indexDocs(writer, docDir);
writer.flush();
//段"_2"形成,由于上次flushDocStores设为true,其域和词向量信息是新创建一个段保存的,却是保存在_1.fdt和_1.fdx中的,这时候才产生了此二文件。
indexDocs(writer, docDir);
writer.flush();
//段"_3"形成,由于上次flushDocStores设为false,其域和词向量信息是共享一个段保存的,也是是保存在_1.fdt和_1.fdx中的
indexDocs(writer, docDir);
writer.commit();
//段"_4"形成,由于上次flushDocStores设为false,其域和词向量信息是共享一个段保存的,也是是保存在_1.fdt和_1.fdx中的。然而函数commit中flushDocStores设为true,也意味着下一个段将新创建一个段保存域和词向量信息,此时DocumentsWriter中docStoreSegment= "_4",也表明了虽然段"_4"的域和词向量信息保存在了段"_1"中,将来的域和词向量信息却要保存在段"_4"中。此时"_4.fdx"和"_4.fdt"尚未产生。
indexDocs(writer, docDir);
writer.flush();
//段"_5"形成,由于上次flushDocStores设为true,其域和词向量信息是新创建一个段保存的,却是保存在_4.fdt和_4.fdx中的,这时候才产生了此二文件。
indexDocs(writer, docDir);
writer.commit();
writer.close();
//段"_6"形成,由于上次flushDocStores设为false,其域和词向量信息是共享一个段保存的,也是是保存在_4.fdt和_4.fdx中的

MySQL functions can be used for data processing and calculation. 1. Basic usage includes string processing, date calculation and mathematical operations. 2. Advanced usage involves combining multiple functions to implement complex operations. 3. Performance optimization requires avoiding the use of functions in the WHERE clause and using GROUPBY and temporary tables.

Efficient methods for batch inserting data in MySQL include: 1. Using INSERTINTO...VALUES syntax, 2. Using LOADDATAINFILE command, 3. Using transaction processing, 4. Adjust batch size, 5. Disable indexing, 6. Using INSERTIGNORE or INSERT...ONDUPLICATEKEYUPDATE, these methods can significantly improve database operation efficiency.

In MySQL, add fields using ALTERTABLEtable_nameADDCOLUMNnew_columnVARCHAR(255)AFTERexisting_column, delete fields using ALTERTABLEtable_nameDROPCOLUMNcolumn_to_drop. When adding fields, you need to specify a location to optimize query performance and data structure; before deleting fields, you need to confirm that the operation is irreversible; modifying table structure using online DDL, backup data, test environment, and low-load time periods is performance optimization and best practice.

Use the EXPLAIN command to analyze the execution plan of MySQL queries. 1. The EXPLAIN command displays the execution plan of the query to help find performance bottlenecks. 2. The execution plan includes fields such as id, select_type, table, type, possible_keys, key, key_len, ref, rows and Extra. 3. According to the execution plan, you can optimize queries by adding indexes, avoiding full table scans, optimizing JOIN operations, and using overlay indexes.

Subqueries can improve the efficiency of MySQL query. 1) Subquery simplifies complex query logic, such as filtering data and calculating aggregated values. 2) MySQL optimizer may convert subqueries to JOIN operations to improve performance. 3) Using EXISTS instead of IN can avoid multiple rows returning errors. 4) Optimization strategies include avoiding related subqueries, using EXISTS, index optimization, and avoiding subquery nesting.

Methods for configuring character sets and collations in MySQL include: 1. Setting the character sets and collations at the server level: SETNAMES'utf8'; SETCHARACTERSETutf8; SETCOLLATION_CONNECTION='utf8_general_ci'; 2. Create a database that uses specific character sets and collations: CREATEDATABASEexample_dbCHARACTERSETutf8COLLATEutf8_general_ci; 3. Specify character sets and collations when creating a table: CREATETABLEexample_table(idINT

To safely and thoroughly uninstall MySQL and clean all residual files, follow the following steps: 1. Stop MySQL service; 2. Uninstall MySQL packages; 3. Clean configuration files and data directories; 4. Verify that the uninstallation is thorough.

Renaming a database in MySQL requires indirect methods. The steps are as follows: 1. Create a new database; 2. Use mysqldump to export the old database; 3. Import the data into the new database; 4. Delete the old database.


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