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2014, Sunday May 18

New sample for JSON performance: mORMot vs SuperObject/XSuperObject/dwsJSON/DBXJSON

We have just added a new "25 - JSON performance" sample to benchmark JSON process, using well most known Delphi libraries...

A new fight
featuring
mORMot vs SuperObject/XSuperObject/dwsJSON/DBXJSON

On mORMot side, it covers TDocVariant, late binding, TSQLTable, ORM, record access, BSON...

We tried to face several scenarios:

  • parse/access/write iteration over a small JSON document,
  • read of deeply nested 680 KB JSON (here mORMot is slower than SO/dwsJSON),
  • read of one 180 MB JSON file (with on-the-fly adaptation to fit a record layout),
  • named access to all rows and columns of a 1 MB JSON table, extracted from a SQL request (with comparison with our ORM performance).

On average and in details, mORMot is the fastest in almost all scenarios (with an amazing performance for table/ORM processing), dwsJSON performs very well (better than SuperObject), and DBXJSON is the slowest (by far, but XE6 version is faster than XE4).

Continue reading...

2014, Friday February 28

Are NoSQL databases ACID?

One of the main features you may miss when discovering NoSQL ("Not-Only SQL"?) databases, coming from a RDBMS background, is ACID.

ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably. In the context of databases, a single logical operation on the data is called a transaction. For example, a transfer of funds from one bank account to another, even involving multiple changes such as debiting one account and crediting another, is a single transaction. (Wikipedia)

But are there any ACID NoSQL database?

Please ensure you read the Martin Fowler introduction about NoSQL databases.
And the corresponding video.

First of all, we can distinguish two types of NoSQL databases:

  1. Aggregate-oriented databases;
  2. Graph-oriented databases (e.g. Neo4J).

By design, most Graph-oriented databases are ACID!
This is a first good point.

Then, what about the other type?
In Aggregate-oriented databases, we can identify three sub-types:

  • Document-based NoSQL databases (e.g. MongoDB, CouchDB);
  • Key/Value NoSQL databases (e.g. Redis);
  • Column family NoSQL databases (e.g. Cassandra).
Whatever document/key/column oriented they are, they all use some kind of document storage.
It may be schema-less, blob-stored, column-driven, but it is always some set of values bound together to be persisted.
This set of values define a particular state of one entity, in a given model.
Which we may call Aggregate.

Continue reading...

2014, Tuesday February 25

TDocVariant custom variant type

With revision 1.18 of the framework, we just introduced two new custom types of variants:

  • TDocVariant kind of variant;
  • TBSONVariant kind of variant.

The second custom type (which handles MongoDB-specific extensions - like ObjectID or other specific types like dates or binary) will be presented later, when dealing with MongoDB support in mORMot, together with the BSON kind of content. BSON / MongoDB support is implemented in the SynMongoDB.pas unit.

We will now focus on TDocVariant itself, which is a generic container of JSON-like objects or arrays.
This custom variant type is implemented in SynCommons.pas unit, so is ready to be used everywhere in your code, even without any link to the mORMot ORM kernel, or MongoDB.

TDocVariant documents

TDocVariant implements a custom variant type which can be used to store any JSON/BSON document-based content, i.e. either:

  • Name/value pairs, for object-oriented documents;
  • An array of values (including nested documents), for array-oriented documents;
  • Any combination of the two, by nesting TDocVariant instances.

Here are the main features of this custom variant type:

  • DOM approach of any object or array documents;
  • Perfect storage for dynamic value-objects content, with a schema-less approach (as you may be used to in scripting languages like Python or JavaScript);
  • Allow nested documents, with no depth limitation but the available memory;
  • Assignment can be either per-value (default, safest but slower when containing a lot of nested data), or per-reference (immediate reference-counted assignment);
  • Very fast JSON serialization / un-serialization with support of MongoDB-like extended syntax;
  • Access to properties in code, via late-binding (including almost no speed penalty due to our VCL hack as already detailed);
  • Direct access to the internal variant names and values arrays from code, by trans-typing into a TDocVariantData record;
  • Instance life-time is managed by the compiler (like any other variant type), without the need to use interfaces or explicit try..finally blocks;
  • Optimized to use as little memory and CPU resource as possible (in contrast to most other libraries, it does not allocate one class instance per node, but rely on pre-allocated arrays);
  • Opened to extension of any content storage - for instance, it will perfectly integrate with BSON serialization and custom MongoDB types (ObjectID, RegEx...), to be used in conjunction with MongoDB servers;
  • Perfectly integrated with our Dynamic array wrapper and its JSON serialization as with the record serialization;
  • Designed to work with our mORMot ORM: any TSQLRecord instance containing such variant custom types as published properties will be recognized by the ORM core, and work as expected with any database back-end (storing the content as JSON in a TEXT column);
  • Designed to work with our mORMot SOA: any interface-based service is able to consume or publish such kind of content, as variant kind of parameters;
  • Fully integrated with the Delphi IDE: any variant instance will be displayed as JSON in the IDE debugger, making it very convenient to work with.

To create instances of such variant, you can use some easy-to-remember functions:

  • _Obj() _ObjFast() global functions to create a variant object document;
  • _Arr() _ArrFast() global functions to create a variant array document;
  • _Json() _JsonFast() _JsonFmt() _JsonFastFmt() global functions to create any variant object or array document from JSON, supplied either with standard or MongoDB-extended syntax.

Continue reading...

2013, Tuesday December 10

JSON record serialization

In Delphi, the record has some nice advantages:

  • record are value objects, i.e. accessed by value, not by reference - this can be very convenient, e.g. when defining a Domain-Driven Design
  • record can contain any other record or dynamic array, so are very convenient to work with (no need to define sub-classes or lists); 
  • record variables can be allocated on stack, so won't solicit the global heap; 
  • record instances automatically freed by the compiler when they come out of scope, so you won't need to write any try..finally Free; end block.

Serialization of record values are therefore a must-have for a framework like mORMot.

In recent commits, this JSON serialization of record has been enhanced.
In particular, we introduced JSON serialization via a new text-based record definition.

Continue reading...

2013, Wednesday October 9

Good old object is not to be deprecated - it is the future

Yes, I know this article title is a huge moment of trolling for most Delphi developer.
But object could be legend... - wait for it - ... dary!

You perhaps already noticed by several blog posts here that I still like the good old (and deprecated) object type, in addition to the common heap-allocated class type.
Plain record with methods does not match the object-oriented approach of object, since it does not feature inheritance.

When you take a look at modern strongly-typed languages, targeting concurrent programming (you know, multi-thread/multi-core execution), you will see that the objects may be allocated in several ways, to facilitate execution flow.

The Rust language for instance is pretty interesting. It has optional task-local Garbage Collection and safe pointer types with region analysis.

To some extent, it is very similar to what object allows in the Delphi world, and why I'm still using/loving it!

Continue reading...

2013, Saturday May 11

Delphi XE4 NextGen compiler: using byte instead of ansichar?

When I first read the technical white paper covering all of the language changes in XE4 for mobile development (tied to the new ARM LLVM-based Delphi compiler), I have to confess I was pretty much confused.

Two great mORMot users just asked for XE4/iOS support of mORMot.

Win32/Win64 support for XE4 will be done as soon as we got a copy of it.
I suspect the code already works, since it was working as expected with XE3, and we rely on our own set of low-level functions for most internal work.

But iOS-targetting is more complex, due to the NextGen compiler, mainly.

Continue reading...

2013, Thursday March 7

64 bit compatibility of mORMot units

I'm happy to announce that mORMot units are now compiling and working great in 64 bit mode, under Windows.
Need a Delphi XE2/XE3 compiler, of course!

ORM and services are now available in Win64, on both client and server sides.
Low-level x64 assembler stubs have been created, tested and optimized.
UI part is also available... that is grid display, reporting (with pdf export and display anti-aliasing), ribbon auto-generation, SynTaskDialog, i18n... the main SynFile demo just works great!

Overall impression is very positive, and speed is comparable to 32 bit version (only 10-15% slower).

Speed decrease seems to be mostly due to doubled pointer size, and some less optimized part of the official Delphi RTL.
But since mORMot core uses its own set of functions (e.g. for JSON serialization, RTTI support or interface calls or stubbing), we were able to release the whole 64 bit power of your hardware.

Delphi 64 bit compiler sounds stable and efficient. Even when working at low level, with assembler stubs.
Generated code sounds more optimized than the one emitted by FreePascalCompiler - and RTL is very close to 32 bit mode.
Overall, VCL conversion worked as easily than a simple re-build.
Embarcadero's people did a great job for VCL Win64 support, here!

Continue reading...

2012, Sunday May 20

Recursive calls and private objects

In a Stack Overflow question, someone asked about some nested procedure call he found out. That is, a procedure inside another procedure.

He found out this coding style to be messy, which sounds like a reasonable opinion. But his alternative proposal of putting the internal procedure outside the main one, i.e. making it global, is IMHO even worse.

In some case, a private class, or even record or object with methods is an handy and maintainable implementation pattern.

Continue reading...

2012, Friday April 13

Custom JSON serialization of any class

By default, our mORMot framework is able to serialize any class into a true JSON object.

All published properties will be written as JSON object members.

In some cases, it may be handy to have a custom serialization, for instance if you want to manage some third-party classes, or to adapt the serialization scheme to a particular purpose, at runtime.

Continue reading...

2012, Thursday April 12

Custom JSON serialization of any dynamic array content

One nice feature of the TDynArray wrapper and its associated methods, as defined and used in our framework, is the ability to serialize any dynamic array as JSON content.

By default, only "standard" dynamic arrays (like TIntegerDynArray) are serialized as true JSON array: other not known kind of arrays are serialized as binary content, within a Base64 encoding.

This is a very efficient solution for a pure Delphi application, since it will be fast and always works, but won't be easy to deal with from an AJAX client.

Applications can now supply a custom JSON serialization for any other dynamic array, via the TTextWriter.RegisterCustomJSONSerializer() class method.
Two callbacks are to be supplied for a dynamic array type information, in order to handle proper serialization and un-serialization of the JSON array.

Continue reading...

2012, Wednesday February 29

Delphi and interfaces

No, interface(-book) is not another social network, sorry.

In Delphi OOP model, an interface defines a type that comprises abstract virtual methods.
The short, easy definition is that an interface is a declaration of functionality without an implementation of that functionality. It defines "what" is available, not "how" it is made available. This is the so called "abstraction" benefit of interfaces (there are another benefits, like orthogonality of interfaces to classes, but we'll see it later).

In its upcoming 1.16 revision, our mORMot framework is able to use interface for its service definition.

So we'll discuss and introduce this gem available in all modern languages - including Delphi: interfaces.

Continue reading...

2011, Thursday December 8

Avoiding Garbage Collector: Delphi and Apple side by side

Among all trolling subject in forums, you'll find out the great Garbage Collection theme.

Fashion languages rely on it. At the core of the .Net and Java framework, and all scripting languages (like JavaScript, Perl, Python or Ruby), you'll find a Garbage Collector. New developers, just released from schools, do learn about handling memory only in theory, and just can't understand how is memory allocated - we all have seen such rookies involved in Delphi code maintenance, leaking memory as much as they type. In fact, most of them did not understood how a computer works. I warned you this will be a trolling subject.

And, in Delphi, there is no such collector. We handle memory in several ways:

  • Creating static variables - e.g. on the stack, inside a class or globally;
  • Creating objects with class instances allocated on heap - in at least three ways: with a try..finally Free block, with a TComponent ownership model in the VCL, or by using an interface (which creates an hidden try..finally Free block);
  • Creating reference-counted variables, i.e. string, array of, interface or variant kind of variables.

It is a bit complex, but it is also deadly powerful. You have several memory allocation models at hand, which can be very handy if you want to tune your performance and let program scale. Just like manual recycling at home will save the planet. Some programmers will tell you that it's a waste of cell brain, typing and time. Linux kernel gurus would not say so, I'm afraid.

Then came the big Apple company, which presented its new ARC model (introduced in Mac OS X 10.7 Lion) as a huge benefit for Objective-C in comparison with the Garbage Collection model. And let's face it: this ARC just sounds like the Delphi memory model.

Continue reading...

2011, Tuesday December 6

Automatic JOIN query

In mORMot, all the methods available to handle many-to-many relationship (ManySelect, DestGetJoined...) are used to retrieve the relations between tables from the pivot table point of view. This saves bandwidth, and can be used in most simple cases, but it is not the only way to perform requests on many-to-many relationships. And you may have several TSQLRecordMany instances in the same main record - in this case, those methods won't help you.

It is very common, in the SQL world, to create a JOINed request at the main "Source" table level, and combine records from two or more tables in a database. It creates a set that can be saved as a table or used as is. A JOIN is a means for combining fields from two or more tables by using values common to each. Writing such JOINed statements is not so easy by hand, especially because you'll have to work with several tables, and have to specify the exact fields to be retrieved; if you have several pivot tables, it may start to be a nightmare.

Let's see how our ORM will handle it.

Continue reading...

2011, Sunday November 27

SOLID design principles

Delphi is sometimes assimilated to a RAD product - and this is a marketing label - but IMHO Delphi is much more than RAD.
With Delphi, you can make very serious and clean programming.

Including SOLID style of coding.

The acronym SOLID is derived from the following OOP principles (quoted from the corresponding Wikipedia article):

  • Single responsibility principle: the notion that an object should have only a single responsibility;
  • Open/closed principle: the notion that “software entities ... should be open for extension, but closed for modification”;
  • Liskov substitution principle: the notion that “objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program” - also named as "design by contract";
  • Interface segregation principle: the notion that “many client specific interfaces are better than one general purpose interface.”;
  • Dependency inversion principle: the notion that one should “Depend upon Abstractions. Do not depend upon concretions.”. Dependency injection is one method of following this principle.

If you have some programming skills, those principles are general statements you may already found out by yourself. If you start doing serious object-oriented coding, those principles are best-practice guidelines you would gain following.

They certainly help to fight the three main code weaknesses:

  • Rigidity – Hard to change something because every change affects too many other parts of the system;
  • Fragility – When you make a change, unexpected parts of the system break;
  • Immobility – Hard to reuse in another application because it cannot be disentangled from the current application.

Continue reading...

2011, Friday May 20

How to write fast multi-thread Delphi applications

How to make your software run fast, especially in a multi-threaded architecture?

We tried to remove the Memory Manager scaling problems in our SynScaleMM. It worked as expected in a multi-threaded server environment. Scaling is much better than FastMM4, for some critical tests. But it's not ready for production yet...

To be honest, the Memory Manager is perhaps not the bigger bottleneck in Multi-Threaded applications.

Here are some (not dogmatic, just from experiment and knowledge of low-level Delphi RTL) advice if you want to write FAST multi-threaded application in Delphi.

Continue reading...

2011, Saturday March 12

TDynArray and Record compare/load/save using fast RTTI

The SynCommons unit has been enhanced:
- new BinToBase64 and Base64ToBin conversion functions;
- new low-level RTTI functions for handling record types: RecordEquals, RecordSave, RecordSaveLength, RecordLoad;
- new TDynArray object, which is a wrapper around any dynamic array.

With TDynArray, you can access any dynamic array (like TIntegerDynArray = array of integer) using TList-like properties and methods, e.g. Count, Add, Insert, Delete, Clear, IndexOf, Find, Sort and some new methods like LoadFromStream, SaveToStream, LoadFrom and SaveTo which allow fast binary serialization of any dynamic array, even containing strings or records - a CreateOrderedIndex method is also available to create individual index according to the dynamic array content. You can also serialize the array content into JSON, if you wish.

What I like with dynamic arrays is that they are reference-counted, don't need any Create/try..finally...Free code, and are well handled by the Delphi compiler.
They are no replacement to a TCollection nor a TList (which are the standard and efficient way of storing class instances), but they are very handy way of having a list of content or a dictionary at hand, with no class nor properties definition.
You can look at them like Python's list, tuples (via records handling) and dictionaries (via Find method), in pure Delphi. Our new methods (about searching and serialization) allow most usage of those script-level structures in your Delphi code.

Continue reading...

2010, Thursday October 28

"has many" and "has many through" relationships

Extracted from wikipedia, here is a definition of 'many to many' relationships in regular database management:

In systems analysis, a many-to-many relationship is a type of cardinality that refers to the relationship between two entities (see also Entity-Relationship Model) A and B in which A may contain a parent row for which there are many children in B and vice versa. For instance, think of A as Authors, and B as Books. An Author can write several Books, and a Book can be written by several Authors. Because most database management systems only support one-to-many relationships, it is necessary to implement such relationships physically via a third and fourth junction table, say, AB with two one-to-many relationships A -> AB and B -> AB. In this case the logical primary key for AB is formed from the two foreign keys (i.e. copies of the primary keys of A and B).

In our SQLite3 framework, we just created a dedicated class for handling such "many to many" relationships.

Continue reading...

2010, Friday August 6

Save object, stop class hegemony!

In a recent thread in the Embarcadero Discussion Forums, Vedran Vuk posted some questions about object keyword.
His purpose was to use object instead of class to improve speed and memory consumption: 

I do use classes. I just want to use objects on smaller classes that don't really need initialization or RTTI. Plus, I can directly operate on it like a record with no need for constructors and it can be sealed and has inheritance. Every byte matters in this case.

Rudy posted on the EMB forum that

The "object" type is deprecated. As was said, it mainly exists for compatibility with old Turbo Pascal. That is why it is not documented very well. It's use is not promoted.

I have the same requirement sometimes, for example for our framework or for low-level units.
I do like such plain-old object type, and don't want to see this object feature marked as deprecated in future EMB versions.

Continue reading...