indexing

问题 I am curious as to whether CREATE INDEX idx ON tbl (columns); vs. CREATE UNIQUE INDEX idx ON tbl (columns); has a significant algorithmic performance benefit in PostgreSQL or MySQL implementations when scanning the indexed column(s), or whether the UNIQUE keyword simply introduces a unique constraint alongside the index. I imagine it is probably fair to say that there is a marginal benefit insofar as indexes are likely to be internally implemented as some sort of hash 1 -like structure, and

问题 I am using Oracle database. We are seeing frequent failures in calls to our service. When I looked at the logs I am seeing following exceptions on a table java.sql.BatchUpdateException: ORA-00001: unique constraint (DBSCHEMA.IDX_CO_DETAILS) violated. I have checked the Index on the table for index name DBSCHEMA.IDX_CO_DETAILS . It did not include any column's( INCLUDE_COLUMN is null) . How can I know what is this constraint for ? Is it primary key constraint? We are using hibernate for ORM.

问题 Despite what all the documentation says, I'm finding GIN indexes to be significantly slower than GIST indexes for pg_trgm related searches. This is on a table of 25 million rows with a relatively short text field (average length of 21 characters). Most of the rows of text are addresses of the form "123 Main st, City". GIST index takes about 4 seconds with a search like select suggestion from search_suggestions where suggestion % 'seattle'; But GIN takes 90 seconds and the following result

问题 I'm having trouble understanding the difference between the legacy indexing approach and the new indexing approach so perhaps someone could clarify these points for me. My only concern is really how it relates to the Java API and not Cypher queries. Sub-Questions 1) Is Legacy Indexing the same thing as auto-indexing? 2) Is it true that if you are not using auto-indexing then every time you add a node to the graph you must specify whether or not it should be indexed? 3) Am I correct in

问题 I'm having trouble understanding the difference between the legacy indexing approach and the new indexing approach so perhaps someone could clarify these points for me. My only concern is really how it relates to the Java API and not Cypher queries. Sub-Questions 1) Is Legacy Indexing the same thing as auto-indexing? 2) Is it true that if you are not using auto-indexing then every time you add a node to the graph you must specify whether or not it should be indexed? 3) Am I correct in

问题 I've been trying to write my own coprocessor that creates a secondary index using the prePut hook. To start, I've been simply trying to get a prePut coprocessor to work. So far I can have the coprocessor add to the put object passed to it. What i've found is that I cannot get the coprocessor to write to a row separate from what the passed in put object is writing to. Obviously to create a secondary index, I need to figure this one out. Below is the code for my coprocessor, but it doesn't work

问题 I'm currently working on a project to persist data with JPA 2.1 and to search entities using hibernate search 4.5.0.final. After mapping classes and indexing, the searching works fine. However, when I changed the value description of classB from "someStr" to "anotherStr". The database was updated accordingly, but when I checked the index using Luke, classA.classB.description in the index wasn't updated, and the data cannot be searchable by keyword "anotherStr", but can be searchable by

问题 Say I have the following multicolumn Pandas DataFrame: arrays = [['bar', 'bar', 'baz', 'baz', 'foo', 'foo', ], ['one', 'two', 'one', 'two', 'one', 'two', ]] tuples = list(zip(*arrays)) index = pd.MultiIndex.from_tuples(tuples, names=['first', 'second']) df = pd.DataFrame(np.random.randn(8, 6), columns=arrays) bar baz foo one two one two one two 0 1.018709 0.295048 -0.735014 1.478292 -0.410116 -0.744684 1 1.388296 0.019284 -1.298793 1.597739 0.044640 -0.040337 2 -0.151763 -0.424984 -1.322985

问题 Firstly, can anyone explain how unique index works in databases? Suppose I have a User model with a name column and I add a unique index on it but in the model (user.rb) I just have a presence validator on the name field. So now when I'm trying to create two users with same name, I get PGError duplicate key value violates unique constraint "index_users_on_name" So It looks to me like the unique index working same as uniqueness validator (?) If so then what about foreign keys? Lets say I have

问题 I am using Scrapy to scrape data from a web forum. I am storing this data in a PostgreSQL database using SQLAlchemy. The table and columns create fine, however, I am not able to have SQLAlchemy create an index on one of the columns. I am trying to create a trigram index (pg_trgm) using gin. The Postgresql code that would create this index is: CREATE INDEX description_idx ON table USING gin (description gin_trgm_ops); The SQLAlchemy code I have added to my models.py file is: desc_idx = Index(