OT : PDO Large Objects

[Paul Mooring]

Hi Keith,

For the record I wasn't trying to imply that binary data is the *only* use
case for large objects (or streaming in general) but it's far and away the
most common usage pattern.  4kb isn't really a hard limit but most database
systems will consider data larger than 4kb "large" because of file system
block sizes.  A database server is one of those rare use cases where heavy
optimization is important, especially for i/o, so 4kb is called out
specifically because that's more often than not the block size of the
filesystem.  In heavily simplified terms, this means writes over 4kb are
actually multiple writes to disk which can have some interesting
implications for optimized ACID compliant databases.



On Sat, Apr 5, 2014 at 4:21 PM, keith smith <klsmith2020 at yahoo.com> wrote:

> Thank you so much for your feedback.  Seems everyone thinks large objects
> refers to binary.  The question was about the manual saying 4kb is large
> data and referred to texual or binary.  That means a simple blog post could
> be a large object.  http://www.php.net/manual/en/pdo.lobs.php
>
> Maybe I'll be the first on this list to work with PDO.
>
>
> ------------------------
> Keith Smith
>   On Friday, April 4, 2014 4:42 PM, Paul Mooring <paul at getchef.com> wrote:
>  I'm not really a PHP guy, but I do have a couple of thoughts on this.
>  First an explanation of what some of these things are might be in order.
>  PDO is a PHP library (like mysqli or db2) it's definitely a php specific
> thing and sits on top of the database driver.  ODBC is not Windows specific
> it's a common api for working with various data base servers and has
> drivers for all the common SQL servers (MSSQL, MySQL, Postgres, Oracle...).
>  ODBC being an abstraction layer means you miss out on some database
> specific features.  I'm not familiar with the LOB aspect of PDO, but based
> on what you listed above it sounds like that serves as a bonus for PHP
> rather than the database.  Any common RDBMS will have support for data
> types larger than 4K (binary data is the db is pretty common), but you
> generally don't want to load the whole object in memory on the application
>  side (in PHP).  I've not used the PHP streams api either, but streams are
> a concept that exists in most web programming languages and the concept is
> almost always around loading objects a piece at a time and sending it on.
>
> So what you're left with:
>
> - PDO is a PHP class for database abstractions
> - PDO is supposedly the preferred library for accessing your DB in PHP
> - PDO::PARAM_LOB provides and interface for streaming large amounts of
> data out of your DB without eating all your server's memory
>
> Hope that helps.
>
>
> On Fri, Apr 4, 2014 at 2:07 PM, keith smith <klsmith2020 at yahoo.com> wrote:
>
> Hi,
>
> I have a question about PDO.  I've written a class that I have tried to
> fashion after the Active Record design pattern.
>
> I'm hung up on one thing - Large Objects (LOBs).
> http://www.php.net/manual/en/pdo.lobs.php
>
> The documentation says :
>
> At some point in your application, you might find that you need to store
> "large" data in your database. Large typically means "around 4kb or more",
> although some databases can happily handle up to 32kb before data becomes
> "large". Large objects can be either textual or binary in nature. PDO
> allows you to work with this large data type by using the PDO::PARAM_LOB
> type code in your PDOStatement::bindParam() or PDOStatement::bindColumn()
> calls. PDO::PARAM_LOB tells PDO to map the data as a stream, so that you
> can manipulate it using the PHP Streams API.
>
> The examples all use ODBC which is Windows.  I'm using MySql.  The manual
> does not say this limitation is limited to Windows though.
>
> I would like to use PDO with a couple of applications I am creating and
> the data will be larger than 4kb.
>
> Is this a driver thing?
>
> Is it a PHP thing?
>
> I know it is not a MySql limitation because I can define fields larger
> than 4kb.
>
> I'm lost at what this means to me and how to apply this to my DB class.
>
> Any help is much appreciated!!
>
> Keith
>
>
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>
> --
> Paul Mooring
> Operations Engineer
> Chef
>
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-- 
Paul Mooring
Operations Engineer
Chef
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