![]() If each group is large and a small number of groups exist, the cost of incremental sorting is relatively high. Of course, the optimizer in a database is much more complex than the preceding scenario. Moreover, in PostgreSQL's waterfall model executor, we can obtain some result sets without sorting all data, which is very suitable for Top-N queries with the Limit keyword. You can use certain policy control to make the data volume in sorting better fit the current work_mem every time. The advantages of this algorithm are obvious, especially for large data sets, because it can reduce the volume of data sorted each time. When a group of data sets (X,Y) are sorted as X and Y columns, if the current data set has been sorted by the X column, specific sorting is shown in the following figure: (1, 5)Īt this time, you only need to group the data sets by the X column and sort Y columns in each group to obtain a result set based on sorting by X and Y columns, as shown in the following figure: (1, 5) (1, 2) This improvement derives from a native algorithm. A certain degree of deduplication was implemented to B-tree indexes in PostgreSQL 12. In the community, several major versions of PostgreSQL have continuously optimized its occupied space and execution efficiency. Overall, these data types are unsupported primarily because extra conditions are required to determine whether keys of indexes are the same, in addition to values.ī-tree indexes are a default index type in PostgreSQL.
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