In computing, a hash table (hash map) is a data structure used to implement an associative array, a structure that can map keys to values. A hash table uses a hash function to compute anindexinto an array ofbucketsorslots, from which the desired value can be found. 散列(hash)技术:在...
case T_HashJoin: /* try not to be too chatty about this in text mode */ if (es->format != EXPLAIN_FORMAT_TEXT || (es->verbose && ((Join *) plan)->inner_unique)) ExplainPropertyBool("Inner Unique", ((Join *) plan)->inner_unique, es); break; default: break; } /* quals,...
Groups here are defined by the join variables used to build the hash index (See DFEHashIndexBuild for where this hash index might be built.) DFEHashIndexBuild – Builds a hash index over a set of variables as a side-effect. This hash index is typically reused in later operations. (See...
In computing, a hash table (hash map) is a data structure used to implement an associative array, a structure that can map keys to values. A hash table uses a hash function to compute anindexinto an array ofbucketsorslots, from which the desired value can be found. 散列(hash)技术:在...
A hash function is applied to the join column and the result dictates which consumer parallel server process should receive the row. BROADCAST: Broadcast redistribution happens when one of the two result sets in a join operation is much smaller than the other result set. Instead of re...
For example, if a hash aggregate operator is used in the first step of a query plan, full data of downstream operators is required to create a hash table for an aggregate operation. For common queries with filter conditions, data is calculated and returned in real time. In this scenario, ...
The result sorting method, distributed keys, distributed values, and columns that are used to calculate the hash value are displayed in the output results of the EXPLAIN statement. FileSinkOperator (FS): describes the logic of storage operations on final data records. If INSERT statement blocks...
In fact, it's the pointer to the place in the datafile where the row data resides. In new PostgreSQL 8.4, we can employ a window function to assign a seq to each row. This script fills the table with duplicate values (two duplicates for each (txn, detail) pair): ? 1 2 3 4 5 ...
Maps rows to query servers using a hash function on the join key. Used for PARALLEL JOIN or PARALLEL GROUP BY. RANGE Maps rows to query servers using ranges of the sort key. Used when the statement contains an ORDER BY clause. ROUND-ROBIN Randomly maps rows to query servers. BROADCAST ...
The various punctuators defined in C ++ are asterisk ‘*’, braces ‘{ }’, brackets ‘[]’, colon ‘:’, comma ‘,’, ellipsis ‘…‘, equal to ‘=’, semicolon ‘;’, parentheses ‘()’ and pound (hash) ‘#’. You’ll also like: Constants –...