Questions tagged [bitmap-index]

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In PostgreSQL, how can I make Bitmap Index Scan parallelized?

I want to improve the performance of an SQL statement. I am on version 13. Here are the sample codes and the query I am interested in. drop table ords; CREATE TABLE ords ( ORD_ID INT NOT NULL, CUST_ID ...
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PostgreSQL: Bitmap Heap Scan very slow for SELECT using time zone

We have PostgreSQL 11.1 on x86_64-pc-linux-gnu (Red Hat 4.8.5-28), 64-bit. We have a table with quite a lot of data (but not extra huge, e.g. weather data for some locations for one month). There is a ...
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2answers
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Postgres 10.6: Why is a particular partition's index not being used?

I'm truly stumped as to what's causing this issue and hoping for some guidance. Firstly, this is in our STAGE environment and we partition this table based on the createdTime every month. I have ...
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3answers
2k views

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 ...
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1answer
1k 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 ...
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1answer
148 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
30 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 ...
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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 ...
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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 ...
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0answers
215 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 ...
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2answers
4k 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 ...