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Cost of updating secondary indices

First, we show how the dynamic and memory-based ), which improves upon the other two in various cases.

We compare the new structures with the state of the art, showing that they are competitive and outstand in several scenarios, especially on spaces of medium and high dimensionality.

The ZCOUNT command can be used in order to retrieve the number of elements within a given range, without actually fetching the elements, which is also useful, especially given the fact the operation is executed in logarithmic time regardless of the size of the range.

I wouldn't have thought an index-organised table would necessarily be faster to scan to count all the visible tuples.

Logically, it would have to go through the same amount of data, whether it's organised so that data is in b-tree leaf nodes or in the existing heap format.

Metric indices support efficient similarity searches in metric spaces.

This problem is central to many applications, including multimedia databases and repositories handling complex objects.

But this essentially just the same as scanning the tuples on the heap--- they don't magically take up less space because they're now in an "index".

AFAICT the main reason for an index-organised table is that a small table with a single primary-key index will take up 1 page instead of 3, and index scans by primary key may be a bit faster.

Note: Using the ZREVRANGEBYSCORE it is possible to query a range in reversed order, which is often useful when data is indexed in a given direction (ascending or descending) but we want to retrieve information the other way around. However in general we may want to index some field of an object which is stored elsewhere.

Instead of using the sorted set value directly to store the data associated with the indexed field, it is possible to store just the ID of the object.

I do seem to remember the Oracle-related advice I was given for IOTs was that they were intended for static dimension tables, and not general purpose use, partly due to the cost imposed on maintaining secondary indices (I don't think Oracle stores [key,pkey] in IOT secondary indices, but rather some sort of alternative rowid).

Redis is not exactly a key-value store, since values can be complex data structures.

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