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The following commit(s) were added to refs/heads/master by this push: new dc77027 [CARBONDATA-3548] Add spatial-index user guid to doc dc77027 is described below commit dc77027cba5643b9c228668acd306fee3a0a7517 Author: litao <litao_xid...@126.com> AuthorDate: Thu Dec 19 21:12:21 2019 +0800 [CARBONDATA-3548] Add spatial-index user guid to doc Why is this PR needed? Spatial index feature document is not updated yet. What changes were proposed in this PR? updated the document for spatial index feature Does this PR introduce any user interface change? updated the document for psatial index feature. Is any new testcase added? No This closes #3520 Co-authored-by: VenuReddy2103 <venugopalred...@huawei.com> --- docs/images/spatial-index-1.png | Bin 0 -> 1835 bytes docs/images/spatial-index-2.png | Bin 0 -> 16910 bytes docs/spatial-index-guide.md | 97 ++++++++++++++++++++++++++++++++++++++++ 3 files changed, 97 insertions(+) diff --git a/docs/images/spatial-index-1.png b/docs/images/spatial-index-1.png new file mode 100644 index 0000000..7890fc4 Binary files /dev/null and b/docs/images/spatial-index-1.png differ diff --git a/docs/images/spatial-index-2.png b/docs/images/spatial-index-2.png new file mode 100644 index 0000000..d55f01f Binary files /dev/null and b/docs/images/spatial-index-2.png differ diff --git a/docs/spatial-index-guide.md b/docs/spatial-index-guide.md new file mode 100644 index 0000000..a9010a0 --- /dev/null +++ b/docs/spatial-index-guide.md @@ -0,0 +1,97 @@ +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to you under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +# What is spatial index + +[A spatial index](https://gistbok.ucgis.org/topic-keywords/indexing) is a data structure that allows for accessing a spatial object efficiently. It is a common technique used by spatial databases. Without indexing, any search for a feature would require a "sequential scan" of every record in the database, resulting in much longer processing time. In a spatial index construction process, the minimum bounding rectangle serves as an object approximation. Various types of spatial indices ac [...] + + + +# How does CarbonData implement spatial index + +There are many open source implementations for spatial indexing and to process spatial queries. CarbonData implements a different way of spatial index. Its core idea is to use the raster data. Raster is made up of matrix of cells organized into rows and columns(called a grid). Each cell represents a coordinate. And the index for that coodrinate is generated using longitude and latitude, like the [Z order curve](https://en.wikipedia.org/wiki/Z-order_curve). + +CarbonData rasterize the user data during data load into segments. A set of latitude and longitude represents a grid range. The size of the grid can be configured. Hence, the coordinates loaded are often discrete and not continuous. + +Below figure shows the relationship between the grid and the points residing in it. Black point represents the center point of the grid, and the red points are the coordinates at the arbitrary positions inside the grid. The red points can be replaced by the center point of the grid to indicate that the points lies within the grid. During data load, CarbonData generates an index for coordinate according to row and column of the grid(in the raster) where that coordinate lies. These indices [...] + +![File Directory Structure](../docs/images/spatial-index-1.png?raw=true) + +Carbon supports Polygon User Defined Function(UDF) as filter condition in the query to return all the data points lying within it. Polygon UDF takes multiple points(i.e., pair of longitude and latitude) separated by a comma. Longitude and latitude in the pair are separated by a space. And the first and last points in the polygon must be form a closed loop. CarbonData builds a quad tree using this polygon and spatial region information passed while creating a table. The nodes in the quad [...] +The main reasons for faster query response are as follows : +* Data is sorted based on the index values. +* Polygon UDF filter is pushed down from engine to the carbon layer such that CarbonData scans only matched blocklets avoiding full scan. + +![File Directory Structure](../docs/images/spatial-index-2.png?raw=true) + + +# Installation and Deployment + +Geo is a separate module in the Project. It can be included or excluded from the project build based on the requirement. + +## Basic Command + +### Create Table + +Create table with spatial index table properties + +``` +create table source_index(id BIGINT, latitude long, longitude long) stored by 'carbondata' TBLPROPERTIES ( +'INDEX_HANDLER'='mygeohash', +'INDEX_HANDLER.mygeohash.type'='geohash', +'INDEX_HANDLER.mygeohash.sourcecolumns'='longitude, latitude', +'INDEX_HANDLER.mygeohash.originLatitude'='19.832277', +'INDEX_HANDLER.mygeohash.gridSize'='50', +'INDEX_HANDLER.mygeohash.minLongitude'='1.811865', +'INDEX_HANDLER.mygeohash.maxLongitude'='2.782233', +'INDEX_HANDLER.mygeohash.minLatitude'='19.832277', +'INDEX_HANDLER.mygeohash.maxLatitude'='20.225281', +'INDEX_HANDLER.mygeohash.conversionRatio'='1000000'); +``` +Note: `mygeohash` in the above example represent the index name. + +#### List of spatial index table properties + +|Name|Description| +|-----------------------------------|-----------------------------------------------------------------------------------------| +| INDEX_HANDLER | Used to configure Index name. This name is appended to `INDEX_HANDLER` in the subsequent sub-property configurations. `xxx` in the below sub-properties refer to index name.| +| INDEX_HANDLER.xxx.type | Type of algorithm for processing spatial data. Currently, supports only 'geohash'.| +| INDEX_HANDLER.xxx.sourcecolumns | longitude and latitude column names as in the table. These columns are used to generate index value for each row.| +| INDEX_HANDLER.xxx.gridSize | Grid size of raster data in metres. Currently, spatial index supports raster data.| +| INDEX_HANDLER.xxx.minLongitude | Minimum longitude of the gridded rectangular area.| +| INDEX_HANDLER.xxx.maxLongitude | Maximum longitude of the gridded rectangular area.| +| INDEX_HANDLER.xxx.minLatitude | Minimum latitude of the gridded rectangular area.| +| INDEX_HANDLER.xxx.maxLatitude | Maximum latitude of the gridded rectangular area.| +| INDEX_HANDLER.xxx.conversionRatio | Conversion factor. It allows user to translate longitude and latitude to long. For example, if the data to load is longitude = 13.123456, latitude = 101.12356. User can configure conversion ratio sub-property value as 1000000, and change data to load as longitude = 13123456 and latitude = 10112356. Operations on long is much faster compared to floating-point numbers.| +| INDEX_HANDLER.xxx.class | Optional user custom implementation class. Value is fully qualified class name.| + + +### Select Query + +Query with Polygon UDF predicate + +``` +select * from source_index where IN_POLYGON('16.321011 4.123503,16.137676 5.947911,16.560993 5.935276,16.321011 4.123503') +``` + +## Reference + +``` +[1] https://issues.apache.org/jira/browse/CARBONDATA-3548 +[2] https://gistbok.ucgis.org/topic-keywords/indexing +[3] https://en.wikipedia.org/wiki/Z-order_curve +``` \ No newline at end of file