Scalable Database Server, HiRDB Version 8 UAP Development Guide
The following optimization methods affect grouping processing:
If the HiRDB system judges that sort and hash processing for grouping are unnecessary, it selects a method that can process the data faster. For details about grouping processing, see the HiRDB Version 8 Command Reference manual.
Table 4-7 describes the optimization features related to grouping processing methods.
Table 4-7 Optimization features related to grouping processing methods
Optimization method (type of grouping processing method) | Advantages | Disadvantages |
---|---|---|
Omitted (FLOATABLE SORT) | Data can be searched rapidly if the data count values are unevenly distributed among the back-end servers and grouping does not reduce the data count. | If the group count is small and the data count is high, the performance drops because the communication volume increases. |
Rapid grouping processing (HASH) | Data can be searched rapidly when the group count is small. | If the group count is large, the performance drops because the data is grouped by hashing. |
Group processing, ORDER BY processing, and DISTINCT set function processing at the local back-end server (LIST SORT) | Data can be searched rapidly if grouping substantially decreases the data count. Data can also be searched rapidly if the data is grouped by partitioning keys. | If the data count values are unevenly distributed among the back-end servers because of sorting in each back-end server, the performance drops because processing takes a long time in servers that have a high data count. |
Figure 4-14 shows grouping processing when the optimization method is omitted.
Figure 4-14 Grouping processing method when the optimization method is omitted
Figure 4-15 shows grouping processing when rapid grouping processing is applied.
Figure 4-15 Grouping processing when rapid grouping processing is applied
Figure 4-16 shows grouping processing when group processing, ORDER BY processing, and DISTINCT set function processing are applied at the local back-end server. However, this diagram shows the processing when one table is searched.
Figure 4-16 Grouping processing when group processing, ORDER BY processing, and DISTINCT set function processing are applied at the local back-end server
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