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<h1>Itzam/C</h1>
<h2>A Concise Embeddable Database Engine</i></h2>
<p><small><i>This document is a work in progress. I tend to learn by looking at code, and strongly suggest that
you study the examples in the distribution's <b>test</b> directory for working examples of Itzam code.
Yet I know how important hard docs can be, so I'm open to suggestions for improving or updating this document.</i></small></p>
<p>
Itzam/C manages data storage using B-tree indexes,
storing key-value pairs. Keys are identifiers of any fixed-length type for their associated value,
and there is a one-to-one relationship between keys and values. Itzam/C supports
transactions with rollback, multiple threads accessing the same database, and other features not
usually found in small database engines.
</p><p>
In the real world, Itzam/C is the foundation of many business applications, including
mission-critical systems running 24/365.
</p><p>
Itzam is not a SQL database, or something that can be accessed from ADO.
You can build relational (or network, or...) database systems with Itzam as the
underlying mechanic — but that really isn't what Itzam was meant for. The vast majority
of applications do not need Oracle or SQL Server — they need a simple way to associate
information with a key value, for retrieval. This is the niche Itzam occupies.
</p>
<h4>History</h4>
<p>
Itzam has a long and varied history. It began as example code in my first book, <i>C++
Components and Algorithms</i> (1992). The original code was meant to teach C++, yet
several people contacted me asking if they could use it in various projects. Some even
offered to pay for the code.
</p><p>
And so I reworked the book code into something worthy of production code. After many
versions (and a side-trip into Java under the name "Jisp"), I arrived at the Itzam you
see today.
</p><p>
The current reference version is written in C for a variety of reasons. C produces
small code and can be wrapped in various other programming languages. By writing in
Standard C, I maintain portability. The current code has seen production and commercial
use across PCs, cell phones, and Macs.
</p><h4>
Why "Itzam"?
</h4><p>
Naming projects is always difficult; I sometimes think every word in English has been
appropriated by someone. So I've had to stretch my linguistic horizons. "Itzam"
is one of several Mayan words for <i>iguana</i>; given the fondness of iguanas for trees,
and the presence of an iguana in my house, the name seemed rather fitting.
</p><p>
The Itzam logo (and all other site art) was created by my eldest daughter Elora, using a
combination of commercial and open source tools.
</p><h4>
License
</h4><p>
From version 5.1 forward, Itzam is licensed under the FreeBSD License (aka, the Simplified
BSD License). It is as follows:
</p>
<pre>
Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:
1. Redistributions of source code must retain the
above copyright notice, this list of conditions
and the following disclaimer.
2. Redistributions in binary form must reproduce the
above copyright notice, this list of conditions and
the following disclaimer in the documentation and/or
other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY SCOTT ROBERT LADD ``AS IS'' AND ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
EVENT SHALL SCOTT ROBERT LADD OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
The views and conclusions contained in the software and documentation are those
of the author alone, and should not be interpreted as representing the official
policies, either expressed or implied, of anyoen other than Scott Robert Ladd.
</pre>
<p>
Older versions were released under various incarnations of the GPL. I won't bore you with
details of why I've meandered through various Open Source/Free Software licenses; suffice
it to say that the balkanization and politics of the Free Software movement have rubbed
me very raw.
</p><p>
Individual and corporate licensing is available under a closed-source license; I also provide
maintenance contracts and custom development. For such matters, please contact me at
<a href="mailto:scott.ladd@coyotegulch.com"> scott.ladd@coyotegulch.com</a> or
<a href="mailto:scott.ladd@gmail.com">scott.ladd@gmail.com</a>.
</p>
<h4>Basic Concepts and Structures</h4>
<p>
Most of the processes and concepts used in Itzam are the same as those used "under the
hood" by more complex database systems. Itzam is a nuts-and-bolts approach to database
development, providing great flexibility and customization at the expense of
abstraction. You define how data is connected and associated; such control
requires careful understanding of your data.
</p>
<p>
Itzam associates key values with objects serialized in files, by creating one or more
B-tree indexes to connect keys with objects. In many respects, Itzam is very object-oriented,
with functions tied by name to target data structures in much the same way as a C++ program
links methods to class objects.
</p>
<p>
Everything you need is defined in the <code>itzam.h</code> header files. You'll find several data
structures and internal definitions inside; you can safely ignore most of this, since you'll
be working directly with only a few core types and structures.
</p>
<h3>itzam_ref (simple type)</h3>
<p>
By default, an itzam_ref is the address (position) of information
inside an Itzam-defined database. By default, Itzam uses 32-bit file
pointers; defining the preprocessor macro ITZAM64 during compilation
will create an Itzam library that uses 64-bit file pointers. The
32-bit file operations handle files with sizes up to 2,147,483,648
bytes (some file systems may impose a lower limit); using 64-bit file
operations allows access to files up to 9 <em>quintillion</em>
bytes long.
<br><br>
Using 64-bit file pointers will support the growing size of databases
and 64-bit CPUs. Handling 64-bit values imposes a slight performance
and has a significant affect on file size.
<br><br>
In general, <code>itzam_int</code> is simply a synonym for <code>itzam_ref</code>,
reflecting different contexts. An <code>itzam_int</code> is a length or size,
while and <code>itzam_ref</code> is a file reference (position).
</p>
<h3>itzam_status (enum)</h3>
<p>
Most Itzam functions return a status code, which can be set to <code>ITZAM_OKAY</code>, <code>ITZAM_NOT_FOUND</code>, or
any of the other constants found in <code>itzam.h</code>. Note that many functions will call an
error handler function for serious errors; <code>itzam_status</code> is designed for programatic
purpose (e.g., discovering that a key was not found), as opposed to error handling.
</p>
<h3>itzam_datafile (struct)</h3>
<p>
An <code>itzam_datafile</code> is a structured data file for storing fixed- or variable-length records;
it automatically writes new records in space freed by deleted records. This class is useful without
any of the indexing capabilities inherent in <code>itzam_btree</code>. In some applications, it may
be practical to store data in individual <code>itzam_datafile</code>s, indexing
it via one or more <code>itzam_btree</code>s.
</p>
<p>
For the purposes of an <code>itzam_datafile</code>, consider "record" to be nothing more than
a blob of binary data; the semantics of that "blob" is the province of your program. If you're
talking to Itzam from Java, for example, you can serialize objects to and from byte streams
stored in an <code>itzam_datafile</code>.
</p>
<p>
To handle variable-length records, <code>itzam_datafile</code> records the
size of each record. When a record is deleted, the space it occupied is marked as
empty. The file maintains a linked list of deleted record locations and their sizes.
</p>
<p>
Inserting a new record involves a traverse of the deleted list, looking for an empty
record that is large enough to contain the new information. If the deleted list is
empty, or the new record is too large to fit into any open slots, the new object
record is appended to the file.
</p>
<p>
Reusing deleted record space has a drawback: it leaves dead space in the file when
a newly-inserted record is smaller than the "deleted" space it overwrites. Deleted
records also use space in the file until a new record is written into their location.
If your record sizes vary widely, it may make sense to periodically compact the file
by removing the wasted space, eliminating deleted records, and regenerating indexes.
If your records are fixed-length, the data file shouldn't contain much waste space.
</p>
<p>
All functions that directly manipulate datafiles follow the naming pattern <code>itzam_datafile_*</code>.
</p>
<h3>itzam_btree (struct)</h3>
<p>
An <code>itzam_btree</code> organizes keys. A key is a fixed-length datum or data collection that
will be sorted into an order, using a B-tree structure stored in an <code>itzam_datafile</code>.
The order of the keys is determined by a user-defined comparison function. The actual content of
the key is unrestricted, beyond the algorithmic requirement that it be fixed in length. A key
could be a 32-bit numeric serial number and a 32- or 64-bit reference to the associated record.
Or, for small records, the key could contain the entire data, with only "key" elements being
used in the comparison fucntion for ordering and look-up purposes.
</p>
<p>
All functions that directly manipulate B-tree indexes follow the naming pattern <code>itzam_btree_*</code>.
</p>
<h3>itzam_btree_cursor (struct)</h3>
<p>
An <code>itzam_btree_cursor</code> is a list of the records in a database, and can be traversed in key order.
It does not store records; instead, it is a forward and backward traversable list of records in
order (as defined by the database's key comparison function.)
</p>
<p>
When you create an <code>itzam_btree_cursor</code>, it locks the mutex for the B-tree, preventing changes
to that B-tree until the cursor is closed.
</p>
<p>
In many ways, an <code>itzam_btree_cursor</code> can be used like a traditional database cursor.
You can also treat it like a query, filtering records as you iterate through a list of records.
</p>
<p>
All functions that directly manipulate B-tree cursors follow the naming pattern <code>itzam_btree_cursor_*</code>.
</p>
<h4>Example Code</h4>
<p>
Itzam/C includes several test and example programs, found in the <i>test</i> directory of the distribution.
</p>
<h3>itzam_btree_test_stress</h3>
<p>
This program performs a series of random inserts and removes from a B-tree index, verifying the
validity of the database after each action, and using transactions with commits and recalls. It
excercises almost every part of Itzam/C, and demonstrates how to use those features.
</p>
<h3>itzam_btree_insert</h3>
<p>
Created at the behest of several customers, to show how fast raw insertion is. This is simple a
benchmark.
</p>
<h3>itzam_btree_test_threads</h3>
<p>
This program creates multiple threads that sumltaneously insert and rmeove records from the
same B-tree index. Mutexes within Itzam/C control resource access, and shared memory
improves performance.
</p>
<h3>itzam_btree_test_strvar</h3>
<p>
Here is an example of two oft-queried concepts: The use of variable-length string keys, and
the storage of variable-length records. For a simple Itzam
database of fixed-length records (as in the examples above), data can be embedded along with
keys in the B-tree structure. For more complex data bases, the key can be linked to a reference
to its asscoaited data -- in this case, an itzam_ref to a record stored independently with
the B-tree file.
</p><p>
This example also illustrates a key feature of Itzam/C: B-tree files are
also itzam_datafiles, <i>and</i> an itzam_btree index can reference data outside the B-tree
— for example, a position in another fiel that could contain text, other binary data,
or another itzam_datafile.
</p><p>
The B-tree cursor mechanism is also shown in this example.
</p>
<h4>Common Types and Structures</h4>
<h3>itzam_ref</h3>
<p>
By default, an <code>itzam_ref</code> is the address (position) of information
inside an Itzam-defined database. By default, Itzam uses 32-bit file
pointers; defining the preprocessor macro <code>ITZAM64</code> during compilation
will create an Itzam library that uses 64-bit file pointers. The
32-bit file operations handle files with sizes up to 2,147,483,648
bytes (some file systems may impose a lower limit); using 64-bit file
operations allows access to files up to 9,223,372,036,854,775,808
bytes long (again, limited by file system).
<br><br>
Using 64-bit file pointers will support the growing size of databases
and 64-bit CPUs. Handling 64-bit values imposes a slight performance
and has a significant affect on file size.
</p>
<pre>
#if defined(ITZAM64)
typedef int64_t itzam_ref;
#else
typedef int32_t itzam_ref;
#endif
</pre>
<h3>itzam_int</h3>
<p>
An <code>itzam_int</code> is the same type as <code>itzam_ref</code>, but used in a different
context. While an <code>itzam_ref</code> is a file pointer, and <code>itzam_int</code> is a
length, such as the size of a record.
</p>
<pre>
#if defined(ITZAM64)
typedef int64_t itzam_int;
#else
typedef int32_t itzam_int;
#endif
</pre>
<h3>itzam_bool</h3>
<p>
Yes, I know -- another damned boolean type. Here's the problem: different platforms support different <code>
bool</code> implementations of differing sizes. Itzam relies on predictable datum sizes, thus it implements
an explicit boolean type.
</p>
<pre>
typedef int16_t itzam_bool;
static const int16_t itzam_true = -1;
static const int16_t itzam_false = 0;
</pre>
<h3>itzam_state</h3>
<p>
Most Itzam functions return a status code, which can be set to <code>ITZAM_OKAY</code>, <code>ITZAM_NOT_FOUND</code>, or
any of the other constants found in <code>itzam.h</code>. Note that many functions will call an
error handler function for serious errors; <code>itzam_state</code> is designed for programatic
purpose (e.g., discovering that a key was not found), as opposed to error handling.
</p>
<pre>
typedef enum
{
ITZAM_OKAY,
ITZAM_AT_END,
ITZAM_AT_BEGIN,
ITZAM_UNKNOWN,
ITZAM_NOT_FOUND,
ITZAM_DUPLICATE,
ITZAM_32BIT_OVERFLOW
} itzam_state;
</pre>
<h3>itzam_error</h3>
<p>
When Itzam encounters a serious probled, it calls the error handler defined for a given
<code>itzam_datafile</code>. This enumeration identifies the problem.
</p>
<pre>
typedef enum
{
ITZAM_ERROR_SIGNATURE,
ITZAM_ERROR_VERSION,
ITZAM_ERROR_WRITE_FAILED,
ITZAM_ERROR_OPEN_FAILED,
ITZAM_ERROR_READ_FAILED,
ITZAM_ERROR_CLOSE_FAILED,
ITZAM_ERROR_SEEK_FAILED,
ITZAM_ERROR_TELL_FAILED,
ITZAM_ERROR_DUPE_REMOVE,
ITZAM_ERROR_FLUSH_FAILED,
ITZAM_ERROR_TOO_SMALL,
ITZAM_ERROR_NULL_ALLOC,
ITZAM_ERROR_PAGE_NOT_FOUND,
ITZAM_ERROR_LOST_KEY,
ITZAM_ERROR_KEY_NOT_WRITTEN,
ITZAM_ERROR_KEY_SEEK_FAILED,
ITZAM_ERROR_ITERATOR_COUNT
} itzam_error;
</pre>
<h3>itzam_error handler</h3>
<p>
This type defines the signature of an error handling function.
</p>
<pre>
typedef void itzam_error_handler(const char * function_name, itzam_error error);
</pre>
<h4>Common Functions</h4>
<h3>itzam_set_default_error_handler</h3>
<p>
Sets the default error handler. When Itzam creates a new datafile, it assigns the
default handler to the datafile object. You can change the default handler with
this function, or set datafile-specific error handlers with
<code>itzam_datafile_set_error_handler</code>. The default error handler displays
a message to <code>stderr</code> and causes program termination.
</p>
<pre>
void itzam_set_default_error_handler(itzam_error_handler * error_handler);
</pre>
<p><b>Parameters</b><br>
<code>error_handler</code> - Address of user-defined error handler
</p>
<p><b>Return Value</b><br>
None
</p>
<h3>itzam_get_default_error_handler</h3>
<p>
Returns the address of the current default error handler.
</p>
<pre>
itzam_error_handler * itzam_get_default_error_handler();
</pre>
<p><b>Parameters</b><br>
None
</p>
<p><b>Return Value</b><br>
The address of the current default error handler.
</p>
<h4>Datafiles</h4>
<p>
An <code>itzam_datafile</code> is a structured data file for storing fixed- or variable-length records;
it automatically writes new records in space freed by deleted records. This class is useful without
any of the indexing capabilities inherent in <code>itzam_btree</code>. In some applications, it may
be practical to store data in individual <code>itzam_datafile</code>s, indexing
it via one or more <code>itzam_btree</code>s.
</p>
<p>
For the purposes of an <code>itzam_datafile</code>, consider "record" to be nothing more than
a blob of binary data; the semantics of that "blob" is the province of your program. If you're
talking to Itzam from Java, for example, you can serialize objects to and from byte streams
stored in an <code>itzam_datafile</code>.
</p>
<p>
To handle variable-length records, <code>itzam_datafile</code> records the
size of each record. When a record is deleted, the space it occupied is marked as
empty. The file maintains a linked list of deleted record locations and their sizes.
</p>
<p>
Inserting a new record involves a traverse of the deleted list, looking for an empty
record that is large enough to contain the new information. If the deleted list is
empty, or the new record is too large to fit into any open slots, the new object
record is appended to the file.
</p>
<p>
Reusing deleted record space has a drawback: it leaves dead space in the file when
a newly-inserted record is smaller than the "deleted" space it overwrites. Deleted
records also use space in the file until a new record is written into their location.
If your record sizes vary widely, it may make sense to periodically compact the file
by removing the wasted space, eliminating deleted records, and regenerating indexes.
If your records are fixed-length, the data file shouldn't contain much waste space.
</p>
<p>
All functions that directly manipulate datafiles follow the naming pattern <code>itzam_datafile_*</code>.
</p>
<h4>Datafile Types and Structures</h4>
<h3>itzam_datafile</h3>
<p>
This structure encapsulates the elements used internally by Itzam to manipulate a datafile.
</p>
<pre>
typedef struct
{
// you can safely ignore the members
}
itzam_datafile;
</pre>
<h4>Datafile Functions</h4>
<h3>
</h3>
<p>
</p>
<pre>
</pre>
<p><b>Parameters</b><br>
<code></code> - <br>
<code></code> - <br>
</p>
<p><b>Return Value</b><br>
<code></code> <br>
<code></code>
</p>
<h3>itzam_datafile_create</h3>
<p>
Creates a new, empty data file. This function will automatically delete any file named
<code>filename</code>.
</p>
<pre>
itzam_state itzam_datafile_create(itzam_datafile * datafile,
const char * filename);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br><br>
<code>filename</code> - the platform-specific name of the new file
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_open</h3>
<p>
Opens an existing datafile. The file may be open read-only.
</p>
<pre>
itzam_state itzam_datafile_open(itzam_datafile * datafile,
const char * filename,
bool read_only,
bool recover);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
<code>filename</code> - platform-specific name of the file to be opened<br>
<code>read_only</code> - determines if the file is opened read-only (writes disallowed)
<code>recover</code> - if true, the database will rollback any unfinished transactions; if false, the old journal file will simply be removed
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_state itzam_datafile_close</h3>
<p>
Closes an open data file. This flushes any remaining data to external storage.
</p>
<pre>
itzam_state itzam_datafile_close(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_set_error_handler</h3>
<p>
Sets an error handling function specific to a given datafile. If this function is not used,
Itzam supplies a default error function, printing an error message to <code>stderr</code> and calling
<code>exit(1)</code>.
</p>
<pre>
void itzam_datafile_set_error_handler(itzam_datafile * datafile,
itzam_error_handler * error_handler);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
<code>error_handler</code> - the address of an error handler function
</p>
<p><b>Return Value</b><br>
None
</p>
<h3>
itzam_datafile_mutex_lock
</h3>
<p>
Lock the mutex associated with this datafile, preventing other threads from altering the
datafile's resources until an unlock is performed. Several datafile functions lock and unlock
the mutex internally, as needed for resource contention control. As such, it should not
usually be necessary to call this function explicitly.
</p>
<pre>
void itzam_datafile_mutex_lock(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
</p>
<h3>
itzam_datafile_mutex_unlock
</h3>
<p>
Unlock the mutex associated with this datafile, allowing other threads access to the
datafile's resources. Several datafile functions lock and unlock
the mutex internally, as needed for resource contention control. As such, it should not
usually be necessary to call this function explicitly.
</p>
<pre>
void itzam_datafile_mutex_unlock(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
</p>
<h3>itzam_datafile_tell</h3>
<p>
Retrieves the file pointer for a given datafile.
</p>
<pre>
itzam_ref itzam_datafile_tell(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
</p>
<p><b>Return Value</b><br>
The position of the file pointer in <code>datafile</code>.
</p>
<h3>itzam_datafile_seek</h3>
<p>
Sets the file pointer for a given datafile.
</p>
<pre>
itzam_state itzam_datafile_seek(itzam_datafile * datafile,
itzam_ref pos);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
<code>pos</code> - The new position, as calculated from the beginning of the file
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_rewind</h3>
<p>
Sets the file pointer to the beginning of the first active (not deleted) record in a datafile.
</p>
<pre>
itzam_state itzam_datafile_rewind(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_get_next_open</h3>
<p>
Finds a file pointer that can be used to write a record of <code>length</code>
bytes. This will either be a deleted record of at least <code>length</code> bytes,
or the end of the datafile. <i> This fucntion is generally used internally, and should
be used with caution.</i>
</p>
<pre>
itzam_ref itzam_datafile_get_next_open(itzam_datafile * datafile,
itzam_int length);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
<code>length</code> - the required number of bytes
</p>
<p><b>Return Value</b><br>
The file pointer of the first empty record than can hold <code>length</code> bytes,
or <code>ITZAM_NULL_POS</code> if an error occurred.
</p>
<h3>itzam_datafile_write</h3>
<p>
Writes a record to the datafile at the current file position. The record will be stored
in the first deleted record with adequate space, or it will be written to the end of
the file if no adequate deleted record is available.
</p>
<pre>
itzam_ref itzam_datafile_write(itzam_datafile * datafile,
const void * data,
itzam_int length);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
<code>data</code> - a pointer to the record being written<br>
<code>length</code> - the number of bytes pointed to by data
</p>
<p><b>Return Value</b><br>
The file pointer to the beginning of the newly-written record, or
<code>ITZAM_NULL_POS</code> if an error occurred.
</p>
<h3>itzam_datafile_overwrite</h3>
<p>
Overwrite a portion of a record at a gievn offset. The <code>where</code> must point to the
beginning of a valid record, and the <code>offset</code> + <code>length</code> must not
exceed the record's boundaries. This function should be used with caution.</p>
<pre>
itzam_ref itzam_datafile_overwrite(itzam_datafile * datafile,
const void * data,
itzam_int length,
itzam_ref where,
itzam_int offset);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
<code>data</code> - a pointer to the record being written<br>
<code>length</code> - the number of bytes pointed to by data<br>
<code>where</code> - start of header for record being modified<br>
<code>offset</code> - offset in bytes from the beginning of record data where writing should take place
</p>
<p><b>Return Value</b><br>
<codce>ITZAM_TOO_LONG</code> if the overwrite would exceed the record boundaries<br>
<code>ITZAM_OKAY</code> on success
</p>
<h3>itzam_datafile_read</h3>
<p>
Reads the record at the current file pointer in the given data file. This function assumes
that the file pointer is at the beginning of a valid record.
</p>
<pre>
itzam_state itzam_datafile_read(itzam_datafile * datafile,
void * data,
itzam_int max_length);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
<code>data</code> - a pointer to a buffer to contain the read record<br>
<code>length</code> - the maximum number of bytes that can be written to <code>data</code>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_read_alloc</h3>
<p>
Reads the record at the current file pointer in the given data file. This function assumes
that the file pointer is at the beginning of a valid record. Where <code>itzam_datafile_read</code>
requires a pointer to preallocated space, <code>itzam_datafile_read_alloc</code> dynamically
allocates record space based on information stored in the record header. The caller is
responsible for freeing the memory allocated to <code>data</code>.
</p>
<pre>
itzam_state itzam_datafile_read_alloc(itzam_datafile * datafile,
void ** data,
itzam_ref * length);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
<code>data</code> - a pointer to a pointer that references the allocated record buffer<br>
<code>length</code> - the number of bytes allocated to <code>data</code>
<code></code> -
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_remove</h3>
<p>
Deletes the record at the current file pointer in the given data file. This function assumes
that the file pointer is at the beginning of a valid record.</p>
<pre>
itzam_state itzam_datafile_remove(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_commit</h3>
<p>
Forces the datafile to write all data pending in cache to memory.
</p>
<pre>
itzam_state itzam_datafile_commit(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_file_lock</h3>
<p>
Exclusively locks a datafile using OS-level file locking, preventing other processes or threads
from making changes.
</p>
<pre>
itzam_bool itzam_datafile_lock(itzam_datafile * datafile, bool read_only);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure<br>
</p>
<p><b>Return Value</b><br>
<code>itzam_true</code> if the function succeeded<br>
<code>itzam_fale</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_file_unlock</h3>
<p>
Removes an existing OS-level lock from the file.
</p>
<pre>
itzam_bool itzam_datafile_unlock(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure
</p>
<p><b>Return Value</b><br>
<code>itzam_true</code> if the function succeeded<br>
<code>itzam_false</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_transaction_start</h3>
<p>
Begins a new transaction and locks the file. Until a commit or reollback is performed, all changes to the
datafile file are recorded in an external journal file.
</p>
<pre>
itzam_state itzam_datafile_transaction_start(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_transaction_commit</h3>
<p>
Commits the current transaction, which makes all changes permanent.
The temporary journal file is removed, and the file unlocked.
</p>
<pre>
itzam_state itzam_datafile_transaction_commit(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_datafile_transaction_rollback</h3>
<p>
The current transaction is "rolled back", meaning that all changes to the file will be "undone".
The temporary journal file is removed, and the file unlocked.
</p>
<pre>
itzam_state itzam_datafile_transaction_rollback(itzam_datafile * datafile);
</pre>
<p><b>Parameters</b><br>
<code>datafile</code> - a pointer to the target <code>itzam_datafile</code> structure
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h4>B-trees</h4>
<p>
The B-tree data structure maintains a list of keys in order, as determined by a user-supplied
key comparison function. You determine the sort order via the comparison function supplied when
opening or creating an <code>itzam_btree</code>. Just be certain that you always <i>use the same
comparison function whenever making changes to the index.</i>
</p>
<p>
All keys must be unique in a B-tree index.
</p>
<p>
<a href="about_keys.html">More about keys</a>
</p>
<p>
Functions that directly manipulate B-tree indexes follow the naming pattern <code>itzam_btree_*</code>.
</p>
<h4>B-tree Types and Structures</h4>
<h3>itzam_btree</h3>
<p>
For the most part, you won't directly access the members of an <code>itzam_btree</code> structure.
However, it is possible (and often quite desirable) to store non-index data in the same datafile
used by an index. The example program does this very thing, combining contact records with the
name-based B-tree index.
</p>
<pre>
typedef struct
{
itzam_datafile * m_datafile; // file associated with this B-tree file
// The rest is internal stuff
}
itzam_btree;
</pre>
<h3>itzam_key_comparator</h3>
<p>
A B-tree index uses a comparator to determine the relative order of two keys. The user defines and supplies
a comparator function pointer when opening or creating an index; the function's signature must match this type definition.
</p>
<pre>
typedef int itzam_key_comparator(const void * key1, const void * key2);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
<code>filename</code> - the platform-specific name of the file to be created<br>
<code>key_comparator</code> - a function that compares two index keys
</p>
<p><b>Return Value</b><br>
<code>< 0</code>, if <code>key1</code> is before <code>key2</code><br>
<code>= 0</code>, if <code>key1</code> equals <code>key2</code><br>
<code>> 0</code>, if <code>key1</code> is after <code>key2</code>
</p>
<h4>B-tree Functions</h4>
<h3>itzam_btree_create</h3>
<p>
Creates a new B-tree index by creating a data file with a specific internal structure. Keys
will be ordered based on comparisons performed via the called-supplied
<code>key_comparator</code> function.
</p>
<pre>
itzam_state itzam_btree_create(itzam_btree * B-tree,
const char * filename,
uint16_t order,
itzam_int key_size,
itzam_key_comparator * key_comparator,
itzam_error_handler * error_handler);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
<code>filename</code> - the platform-specific name of the file to be created<br>
<code>key_size</code> - the number of bytes in key objects; all keys must be of this exact size<br>
<code>order</code> - the number of keys held in each B-tree page; the predefined constant
<code>ITZAM_BTREE_ORDER_DEFAULT</code> works well for most indexes<br>
<code>key_comparator</code> - a function that compares two index keys
<code>error_handler</code> - the function to be called when a fatal error occurs in Itzam
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_btree_open</h3>
<p>
Opens an existing B-tree index file. The <code>key_comparator</code> function must
produce the same results as the comparison functions used in previous manipulations
of the index. In other words, always use the same <code>key_comparator</code>
function for a given index.
</p>
<pre>
itzam_state itzam_btree_open(itzam_btree * B-tree,
const char * filename,
itzam_key_comparator * key_comparator,
itzam_error_handler * error_handler,
itzam_bool recover,
itzam_bool read_only);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
<code>filename</code> - the platform-specific name of the file to be opened<br>
in a faster the index and a bigger the datafile<br>
<code>key_comparator</code> - a function that compares two index keys<br>
<code>read_only</code> - if true, the file will be opened read-only (no writes allowed);
this is handled internally to ITzam, and only prevents this specific itzam_btree from
performing inserts and removes.<br>
<code>recover</code> - if true, any unfinished transactions will be rolled back; if false, existing
transaction files are simply deleted
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_btree_close</h3>
<p>
Closes an open B-tree file and flushes any remaining file operations.
</p>
<pre>
itzam_state itzam_btree_close(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>
itzam_btree_mutex_lock
</h3>
<p>
Lock the mutex associated with this B-tree, preventing other threads from altering the
B-tree's resources until an unlock is performed. Several B-tree functions lock and unlock
the mutex internally, as needed for resource contention control. As such, it should not
usually be necessary to call this function explicitly.<br><br>
This function is a convenience; it simply calls the <code>itzam_datafile_mutex_lock</code>
fucntion for the datafile underlying the B-tree.
</p>
<pre>
void itzam_btree_mutex_lock(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
</p>
<h3>
itzam_btree_mutex_unlock
</h3>
<p>
Unlock the mutex associated with this B-tree, allowing other threads access to the
B-tree's resources. Several B-tree functions lock and unlock
the mutex internally, as needed for resource contention control. As such, it should not
usually be necessary to call this function explicitly.<br><br>
This function is a convenience; it simply calls the <code>itzam_datafile_mutex_unlock</code>
fucntion for the datafile underlying the B-tree.
</p>
<pre>
void itzam_btree_mutex_unlock(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
</p>
<h3>itzam_btree_count</h3>
<p>
Returns the number of active keys stored in the B-tree.
</p>
<pre>
uint64_t itzam_btree_count(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure
</p>
<p><b>Return Value</b><br>
The number of active keys in the B-tree.
</p>
<h3>itzam_btree_ticker</h3>
<p>
Returns a count of the number of times a key has been added to the B-tree.
</p>
<pre>
uint64_t itzam_btree_ticker(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure
</p>
<p><b>Return Value</b><br>
The number of times a key has been added to the B-tree.
</p>
<h3>itzam_btree_insert</h3>
<p>
Adds a new record reference to the index, with a given key. The index does not place any
semantics on the value of <code>reference</code>; it is merely stored in association with
<code>key</code>. The <code>reference</code> can be a file pointer in <code>B-tree->m_datafile</code>
or a file position in another datafile, or any other 64-bit value of the caller's choosing.
</p>
<pre>
itzam_state itzam_btree_insert(itzam_btree * B-tree,
const void * key);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
<code>key</code> - a pointer to the key data that identify the record reference<br>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_btree_find</h3>
<p>
Finds the record reference associated with a given key.
</p>
<pre>
itzam_ref itzam_btree_find(itzam_btree * B-tree,
const void * search_key
void * result);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
<code>search_key</code> - a pointer to the key data that identifies the record
<code>result</code> - a pointer to key data that will be updated with the contents found by searchign for <code>search_key</code>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_btree_remove</h3>
<p>
Removes the first key found that is associated with the given <code>key</code>.
If <code>ref</code> is NULL, the function also attempts to remove the associated
record from the <code>B-tree->m_datafile</code>. If <code>ref</code> is not NULL,
this function returns the record reference associated with the deleted key.
</p>
<pre>
itzam_state itzam_btree_remove(itzam_btree * B-tree,
const void * key);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
<code>key</code> - a pointer to the key data that identifies the record<br>
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_btree_file_lock</h3>
<p>
A simple wrapper for <code>itzam_datafile_file_lock</code>.
</p>
<pre>
itzam_bool itzam_btree_lock(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure<br>
</p>
<p><b>Return Value</b><br>
<code>itzam_true</code> if the function succeeded<br>
<code>itzam_false</code> the function failed; <code>B-tree</code> is in an unknown state
</p>
<h3>itzam_btree_file_unlock</h3>
<p>
A simple wrapper for <code>itzam_datafile_file_unlock</code>.
</p>
<pre>
itzam_bool itzam_btree_unlock(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure
</p>
<p><b>Return Value</b><br>
<code>itzam_true</code> if the function succeeded<br>
<code>itzam_false</code> the function failed; <code>B-tree</code> is in an unknown state
</p>
<h3>itzam_btree_transaction_start</h3>
<p>
Begins a new transaction and locks the file. Until a commit or reollback is performed, all changes to the
B-tree file are recorded in an external journal file.
</p>
<pre>
itzam_state itzam_btree_transaction_start(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_btree_transaction_commit</h3>
<p>
Commits the current transaction, which makes all changes permanent.
The temporary journal file is removed, and the file unlocked.
</p>
<pre>
itzam_state itzam_btree_transaction_commit(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
<h3>itzam_btree_transaction_rollback</h3>
<p>
The current transaction is "rolled back", meaning that all changes to the file will be "undone".
The temporary journal file is removed, and the file unlocked.
</p>
<pre>
itzam_state itzam_btree_transaction_rollback(itzam_btree * B-tree);
</pre>
<p><b>Parameters</b><br>
<code>B-tree</code> - a pointer to the target <code>itzam_btree</code> structure
</p>
<p><b>Return Value</b><br>
<code>ITZAM_OKAY</code> if the function succeeded<br>
<code>ITZAM_UNKNOWN</code> the function failed; <code>datafile</code> is in an unknown state
</p>
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