Questions tagged [bitmap-index]

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Indexing of a PostgreSQL bitstring (up to 20,000 bits each)

I am building a table that contains chemical compounds (many millions of rows) and of those compounds certain predetermined features/fragments are flagged in a fixed length bitstring. This bitstring ...
2
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1answer
609 views

When PostgreSQL will use Index Only Scan over Bitmap Index + Heap Scan

Today I've been doing some reading on the difference between the two and I think I've got a reasonable idea of each. Index Only: Accesses heap pages as it moves through the index, possibly access the ...
1
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1answer
141 views

Mapping between each bit in a bitmap index and tuple-pointers

Bitmap Indexes are described here, but I don't understand some part of it. A plain indexscan fetches one tuple-pointer at a time from the index, and immediately visits that tuple in the table. A ...
2
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1answer
25 views

Why does PSQL not allow hash indexes with Bitmapscan?

For doing a simple equality query such as EXPLAIN SELECT * FROM table where x = 1; I see that a Bitmap Index scan is done using the BTree indexes. Apparently, Bitmap Index scans disable Hash ...
-1
votes
1answer
1k views

Btree index and Bit Map Index [duplicate]

Please clarify the difference between BitMap Index and Btree index. I am using mysql version 5.5.37-0ubuntu0.12.04.1. I can able to create Btree index but unable to create the same, Please find the ...
0
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2answers
4k views

ON creating BITMAP INDEX on a table in mysql throws error

I have database named "demo_dev" and added a table named "countries". I wanted to create a bitmap index on a column, say, region as it has fewer unique values, using following query. CREATE BITMAP ...
4
votes
0answers
213 views

How to decode a query on a composite unary-encoded attribute?

A good early paper on the topic of bitmap indexes is "Bit Transposed Files" by Wong et al, published in 1985. In all the query-decoding examples, it is left to the reader to understand how each ...
5
votes
2answers
3k views

Cardinality rule for bitmap indexes

The Oracle documentation includes the following advice: A bitmap index should be built on each of the foreign key columns of the fact table or tables In that reference, there is even a bitmap ...