Questions tagged [bitmap-index]
11 questions
9
votes
3 answers
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 will have between 2000 and 20000 bits, further…
Ellert van Koperen
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5
votes
2 answers
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 index on the date column. Whatever happened to…
user1831003
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4
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0 answers
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 decoded query is derived. One of the examples is too…
Iain Samuel McLean Elder
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2
votes
1 answer
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 same page multiple time.
Bitmap Index Scan +…
markdsievers
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2
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1 answer
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 indexes but I'm curious as to why? Wouldn't the query be…
Abundance
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1
vote
2 answers
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 INDEX ON countries (region);
It threw an error as…
user3828646
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1
vote
1 answer
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 bitmap scan fetches
all the tuple-pointers from…
alice
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0
votes
1 answer
PostgreSQL - How to optimize slow Bitmap Heap Scan?
My app is calculating the SuperTrend indicator over the price of multiple cryptocurrencies. I have the following table and indices:
-- DDL generated by Postico 2.1.1
-- Not all database features are supported. Do not use for backup.
-- Table…
Sascha Mayr
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0
votes
2 answers
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 VARCHAR(10) NOT NULL,
ORD_DATE DATE NOT…
JAEGEUN YU
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0
votes
2 answers
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 triple checked the partitions and INDEXes on each and…
daniel9x
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-1
votes
1 answer
Btree index and Bit Map Index
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 below query for Btree index which has been…
Karthick
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