#Indexing

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).

We saw this improvement on our development system and our test system. However, when we moved the code to the production system, the query still took “forever”. What went wrong?

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

^tmp.AI("IP1",1,1) = ""

If I rebuild it wth 

zw ##class(tmp.A).%BuildIndices(,1)

the weird thing is the 

In the previous parts (1, 2) we talked about globals as trees. In this article, we will look at them as sparse arrays.

A sparse array - is a type of array where most values assume an identical value.

In practice, you will often see sparse arrays so huge that there is no point in occupying memory with identical elements. Therefore, it makes sense to organize sparse arrays in such a way that memory is not wasted on storing duplicate values.

Have some free text fields in your application that you wish you could search efficiently?  Tried using some methods before but found out that they just cannot match the performance needs of your customers?  Do I have one weird trick that will solve all your problems?  Don’t you already know!?  All I do is bring great solutions to your performance pitfalls!

As usual, if you want the TL;DR (too long; didn’t read) version, skip to the end.  Just know you are hurting my feelings.

Cache version: Cache for Windows (x86-64) 2017.2.1 (Build 801_3U)

Good Afternoon,
I have a co-worker who is trying to run the below query via ODBC. The issue is that the query appears to be running extremely slow (nearly 2 hours).

 Below is the generated query plan
 

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?

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 ??

Table1.Identifier = Table2.Identifier instead of Table1.Id = Table2.id ??
But I can still use Table1.Id = Table2.Id as cache still made one ID field

So where is PrimaryKey useful in cache?

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? 

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

I'm facing a specific sort problem.
There are several thousands of articles sold all over. 
Users expect to get a description in local language sorted by their specific collation.

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

Hi, Community!

Consider you move data from one server to another or make a deployment with persistent data. What do you do with index globals?

Is it always better to rebuild them or there are some cases when it worth to take them too?

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?

Is there any way to specify in which order indices are built during:

• %BuildIndices
• %Save

So far I think they are built by name order.

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?

Class TestClassIndx Extends %Persistent
{
Property name As %String [ Private ];
Property age As %String [ Private ];
Property country As %String [ Private ];
Index IndextestUniq On (name, age, country) [ Unique ];
}

INSERT INTO TestClassIndx (name,age,country) VALUES ('1','2',NULL)

Best Regards 

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 :)

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?

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

Hi

1. Is it possible do define an index like that :

create index UIX on MyTable (Column1) where Column1 is not null

2. What happens if we add an index on a property that is NOT required, meanning that not all records will be indexed because we do not allow null subscripts ?

Hi, Community!

I just have introduced new tag Indexing which relates to articles and questions on how to introduce, manage and increase performance with Indexing on Caché Objects.

Hi 

I have two persistent classes defined. Lets call it Parent and Child.

Child class is one of the property of Parent Class.

I would like to define a index on Child class.

So what is the default behaviour I defined a index on a non simple data type member?

Any possibility that I could customized the behaviour ? For example. Child class has three properties.

Could I configure the index to index any combinations of these three properties?

Thanks for your help.

Quotes (1NF/2NF/3NF)^ru:

Every row-and-column intersection contains exactly one value from the applicable domain (and nothing else). The same value can be atomic or non-atomic depending on the purpose of this value. For example, “4286” can be

• atomic, if its denotes “a credit card’s PIN code” (if it’s broken down or reshuffled, it is of no use any longer)
• non-atomic, if it’s just a “sequence of numbers” (the value still makes sense if broken down into several parts or reshuffled)

This article explores the standard methods of increasing the performance of SQL queries involving the following types of fields: string, date, simple list (in the $LB format), "list of <...>" and "array of <...>".

Sometimes, it comes in very handy (especially for the EAV model) to use array properties in a class and be able to qickly search by their elements: both the key and the value.

Let’s take a look at a simple example:

Overview

Encryption of sensitive data becomes more and more important for applications. For example patient names, SSN, address-data or credit card-numbers etc..

Cache supports different flavors of encryption. Block-level database encryption and data-element encryption. The block-level database encryption protects an entire database.  The decryption/encryption is done when a block is written/read to or from the database and has very little impact on the performance.

Hi!

Consider I have a class Package.Data with Property UniqueStringValue as %String.

I introduced the Index for this property:

 Index ValueIndex on UniqueStringValue [Unique];

It works well.  But if I try to check if there is an object with the certain value in code like this:

if ##class(Package.Data).ValueIndexExists(value)  

this expression fails, if value="value", even if there is an instance with instance.UniqueStingValue="Value"

How can I set the index to prevent saving case sensitive values in this class?

I have a class which defines a property as array of %String. Is it possible to index values of this property and use this property in SQL?

I have tried 'Index idx On prop(ELEMENTS)' and then a select from the generated collection table, but this is still orders of magnitude slower than queries to the containing class.

Hello Fellow Cache Developers:  

Has anyone ever created an index on values of a list property?   If so, would you be willing to share an example?

Also, feel free to offer input and suggestions regarding use of indexes on List values.

Here is my database scenario:

Parent Class:

PropertyA - %String  

PropertyB - %Integer 

Child Class:

PropertyC - %Integer

PropertyD - list of %Integer

Data illustration:

PropertyA + PropertyB   maps to one or more occurrences of [PropertyC + list of values for PropertyD]

ABC + 90001000    maps to  6600012113 + list (86001000, 86982277, 86982271)

Earlier in this series, we've presented four different demo applications for iKnow, illustrating how its unique bottom-up approach allows users to explore the concepts and context of their unstructured data and then leverage these insights to implement real-world use cases. We started small and simple with core exploration through the Knowledge Portal, then organized our records according to content with the Set Analysis Demo, organized our domain knowledge using the Dictionary Builder Demo and finally build complex rules to extract nontrivial patterns from text with the Rules Builder Demo.

I have a production system that has a large dataset of about 2 million rows. I need to create an index on a property but don't want it available to queries until the index is fully populated. Is there a way I can create the indexed, fire off the build, then "activate" the index so queries can use it.

The object and relational data models of the Caché database support three types of indexes, which are standard, bitmap, and bitslice. In addition to these three native types, developers can declare their own custom types of indexes and use them in any classes since version 2013.1. For example, iFind text indexes use that mechanism.