Changes between Version 16 and Version 17 of ImplementSortingMethodsBeforeGistIndexBuilding

Timestamp:

Aug 23, 2021, 6:08:56 AM (3 years ago)

Author:

HanwGeek

Comment:

—

ImplementSortingMethodsBeforeGistIndexBuilding

@@ -122 +122 @@
 * Finish the documents
 
+=== Final Report ===  
+**Abstract**
+
+GiST(Generalized Search Tree) is a generalization data structure of a variety of disk-based height-balanced search trees. Under the high-level API of GiST, structures like b-tree, r-tree can be implemented for data management. PostgreSQL defines a set of process function APIs for elements of the GiST index. Only with these function implementations can a data type be indexed and managed by a GiST structure. In large data scenarios, pre-sorting a batch of data fetched in memory may be a local approximation to the global sorting method. Recent PostgreSQL patch shows that it should speed up the build of a GiST index after some pre-sorting of the data which needs to be indexed. In one fork, the author replaces the GIST_OPTIONS_PROC with GIST_ORDER_PROC to try to define an order for data fetched in memory to sort in order to speed up the subsequent index building process. And I implemented pre-sorting methods in z-order pattern and Hilbert order pattern, Alos tested and compared pre-sorting methods on various data.
+
+**Links**
+
+* Code Base: https://github.com/postgis/postgis/pull/619
+* Wiki: https://trac.osgeo.org/postgis/wiki/ImplementSortingMethodsBeforeGistIndexBuilding
+* Test Results and Performance Comparison: https://docs.google.com/document/d/1_mY_F2hPDk3vmXH5PPp2z9BuQWt-ZMORk6KxtdVQ3HY/edit?usp=sharing
+
+**Conclusion**
+
+* The Morton/Hilbert hash function for pre-sorting can accelerate the process of index building process and reduce the time-consuming to one-third to one-fifth of the original
+* The query operation for different data in the same area demonstrates more stable performance
+* The query performance of pre-sorting is about 30% slower than the original
+
+**Future Work**
+
+* Try to figure out the reason for the slowness of the pre-sorting index
+* Implement a fast Morton/Hilbert hash function for n-dimension geometry objects
+
 == Student's Biography ==
 My name is Han WANG. I am a first year graduate student majoring in GIS at Peking University, and will get my Master's degree in 2023. And this is my github(https://github.com/HanwGeek) and my linkedin(https://www.linkedin.com/in/hanwgeek/). I am interested in all cool things. And it is very exciting to join the open source community! My research interest includes massive spatial temporal data management and analysis. Currently, I am working on a machine learning project based on big trajectory data, which is stored in PostgreSQL database and managed by PostGIS.