Suppose you have an application that allows users to write posts and comment on them. (Wait... that sounds familiar...)

For a given user, you want to be able to list all of the published posts with which that user has interacted - that is, either authored or commented on. How do you make this as fast as possible?

Here's what our %Persistent class definitions might look like as a starting point (storage definitions are important, but omitted for brevity):

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InterSystems FAQ rubric

For volatile tables (tables with many INSERTs and DELETEs), storage for bitmap indexes can become inefficient over time.

For example, suppose that there are thousands of data with the following definition, and the operation of bulk deletion with TRUNCATE TABLE after being retained for a certain period of time is repeatedly performed.

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An interesting pattern around unique indices came up recently (in internal discussion re: isc.rest) and I'd like to highlight it for the community.

As a motivating use case: suppose you have a class representing a tree, where each node also has a name, and we want nodes to be unique by name and parent node. We want each root node to have a unique name too. A natural implementation would be:

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Hi!

I'd like to know if there are any issues if an index is inserted into a table without running the %BuildIndices() method.

It's important to note that data inserted before the index is not important for retrieval, so it's not a problem data inserted before the index don't show up in queries.

The reason why I'm asking this is that I'd like to avoid index reconstruction on big tables which I need to inser such index.

I'm using Cache 2018.1.

Thanks,

José

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Article
· Feb 2, 2021 12m read
A custom SQL index with Python features

Image search like Google's is a nice feature that wonder me - as almost anything related to image processing.

A few months ago, InterSystems released a preview for Python Embedded. As Python has a lot of libs for deal with image processing, I decided to start my own attemptive to play with a sort of image search - a much more modest version in deed :-)

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I'm using Cache SQL and want the ability to choose a specific index.

I've boiled the problem down to one table and simplified the query down to

SELECT *
FROM Registration.PatResp
WHERE SchedApptNum=8450022

SchedApptNum is indexed, but instead of using that column, "Show Plan" indicates that it's looping through the entire Registration.PatResp table on Id (the primary key for the table).

I've done a tune-table with no change.

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Question
· Dec 26, 2019
Performant index on date field

Is there a way to get a good performing index on a date field? I have tried various date property indexes and the query plan is always in a pretty high range. Below are query plan result values I have observed:

StartDate > '2019-12-01' --cost = 699168
StartDate = '2019-12-21' --cost 70666
StartDate between '2019-12-21' and '2019-21-28' --cost = 492058

The query plans above were for type %TimeStamp.

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Our team is reworking an application to use REST services that use the same database as our current ZEN application. One of the new REST endpoints uses a query that ran very slowly when first implemented. After some analysis, we found that an index on one of the fields in the table greatly improved performance (a query that took 35 seconds was now taking a fraction of a second).

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Hello, community!

I've stumbled on some unexpected behavior, and decided to check with you if this is normal. Basically, I'm rebuilding indices and the result is not journaling (which leads to missing indices at shadow server).

The $ZV is "Cache for UNIX (Red Hat Enterprise Linux for x86-64) 2015.2.1 (Build 705U) Mon Aug 31 2015 16:53:38 EDT"

I have an example class

Class tmp.A As %Persistent;

Index IP1 On P1;

Property P1 As %String;

for example there is one object which have P1 = 1, so

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Question
· Mar 29, 2019
Ensemble as a Data lake

We have been storing raw messages in a MySQL database for DR and ad hoc purposes. We are thinking of using an Ensemble instance as our data lake instead. We could segregate the source data by namespace or by global. But either way we'll want a custom global to index the data for data retrieval performance purposes.

Anyone else taking this approach? Any feedback?

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Question
· Mar 5, 2019
PrimaryKey vs Idkey

Just wondering an Insight in the difference between these two indexes

IdKey / PrimaryKey
=================

Property Identifier As %Integer

Index Index1 on Identifier [Idkey]

Index Index2 on Identifier [PrimaryKey]

What's the difference?

1. If I don't have Index1 and only have Index2, then cache does still make its own id.
So how and why do I ever use the PrimaryKey. In Joins ??

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Hi,

I know of the existance of (ELEMENTS) to create an index from a list, but I actually would like to index the content of an element of a list. Is it possible?

My scenario:

Class:
Property Test As list of TestList;

Test.List:
Property Name As %String;
Property Surname As %String;

I would like to have an index based on the TestList.Name. If I try using

Index NewIndex On Test(ELEMENTS)

it will create an index with Name and Surname in it, but I just want to have an index with the name. Is it possible?

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I have a persistent class that represents cities across the United States. It is below, but basically has a City Id, Name, Lat, Lon and a few other unimportant fields for this issue. Anytime I attempt to query on the Latitude or Longitude it immediately returns no results. My first thought was that it was a casting issue so I tried casting both sides to floats, ints, even strings and in all cases it immediately comes back with no results. I then decided to cast it to a string and attempt a like statement thinking it might be something about how floats are handled, but still no joy. Any

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Question
· Apr 15, 2018
Indexes in Cache Objects

Hi-

I have the following objects

Class A

Property P1 As B

Property P2 As %String

Property P3 As %String

Class B

Property P1 As %String

Can I create an index in Class A based on P1.P1. Basically I want an index of class A by property P1 in class B

I tried creating the following but got a compile error

Index I1 On P1.P1

Thanks

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Question
· Nov 23, 2017
Indexing null value

Dear community!

I have problem with index NULL value. Unique index doesn't work for this case. If I use insert and one of parameter is "NULL". Message of constraint doesn't appear and row is inserted into table successfully. How Can I use index with NULL?

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Hi, folks!

Suppose you have a Caché class with %String property which contains relatively large text (from 10 to 2000 symbols).

The class:

Class Test.Duplicates Extends %Persistent 

{

Property Text As %String (MAXLEN = 2000);

}

And you have thousands of entries.

What are the best options to find entries which are duplicates on this property?

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Hi,

I have a class with around 400k lines and 60 columns. Class storage is Cache SQL storage (Mapped from a global).

I want to create multiple indices on certain fields.

I am familiar with two approaches:

1. Create a new map (Index type) on a pointer global.

2. Create a bitmap index

Which approach is more recommended to be used in the case I described? If there are any other approaches, I will be happy to hear.

Thanks :)

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Hi guys!


Unique, PrimaryKey and IDKey?
In what contexts does it apply?

IDKey sets the registry key access to the store.
PrimaryKey, Unique, and IDKey define the uniqueness in the records, but what is correct?

I use everyone? What is the context of each?

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Hi,

I am new to Cache' MV but have extensive experience with other Pick flavors especially Unidata.

I need to determine the impact of adding several indexes to a large file with over 51,000,000 records.

On other systems, I could use FILE.STAT, ANALYZE.FILE and shell to the OS to determine how large the index file was.

None of those seem to be available in Cache' MV. Shelling to the OS just tells me the size of CACHE.DAT.

What is the best way to determine what the disk impact would be if I added an index (CREATE-INDEX) to a file?

TIA,

Steve

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