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Introduction In this article, we will learn about Merge Join. How It Works Simply put, how Merge Join works is like sorting two lists in ascending order first, then placing them side by side for comparison. Assuming we need to compare the id column of two tables, A and B, the specific process is as follows: Step 1: Sort Phase PostgreSQL must ensure that both lists are already sorted by the order of the join column (for example, from smallest to largest). If the two tables are already sorted, such as when the join column is a Primary Key or has an Index, Postgres will skip this step and jump to step 2. Step 2: Merge Phase PostgreSQL will place two pointers starting from the first row of the two tables and begin comparing: If the results on both sides are equal: Return the result, then move the pointer in table B to the next row to continue checking (since data in a column can be duplicated). If the id in table A is smaller: Move the table A pointer to the next row. If the id in table A ...

Introduction In this article, we will continue to explore how to use GIN Index with the text data type First, please note that GIN Index only works with multi-valued data types, meaning fields containing multiple values, so you can easily create an index with the array type However, if you create a similar index with the text type, an error will be reported because text is only a single-valued type, containing only one content string, so you must pass an additional function that defines how to split the text value into items in an array before the index can be created If you remember, when using GIN Index with a text array, you will encounter limitations regarding partial search and must enter the exact word to search for it to work, now you can solve that problem by using text combined with two functions, to_tsvector and pg_trgm Full-Text Search This method uses the to_tsvector function and its index creation process will be as follows Tokenization & Normalization Split the text...

Introduction Index When creating an Index, PostgreSQL creates a separate physical file on the disk. Each index has a Relfilenode which is a unique identifier number. An index does not store the entire information of a row but only contains Index Entries, each entry including: Key: The value of the column you index. TID (Tuple Identifier): A physical pointer consisting of a BlockNumber and an OffsetNumber, used for reference to point to the location of that row in the main table (HEAP). When executing a query, the Query Planner Cost Model in Postgres will calculate to choose between reading data from the index or retrieving it directly from the HEAP (Sequential Scan). {Index Scan Cost} = {Index file reading cost} + {Random block reading cost in the table} {Seq Scan Cost} = {Sequential block reading cost in the table} Because the Index only contains the TID to point to the data in the main table, after loading the index content and finding the necessary values, it must perform random I...