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Solr Notes about Memory Allocation and interaction with HashTables
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The following notes are for C-space PHP developers.

If you are not really familiar with how the Zend HashTable API or the
memory allocation marcros really works, please take sometime to read the notes below :

This is correct as of Zend Engine version 2.3.0

- If memory was allocated with emalloc(), it has to be freed with efree().

- If memory was allocated using pemalloc(), the same value for the persistent
parameter must be used during pefree() to deallocated the allocated memory.
The memory manager for the Zend API will then decide whether to use free() or
efree() depending on whether persistent is 1 or 0 respectively. The same
principle applies to pestrdup(), pecalloc() and the other memory allocation
macros.

- When inserting values into the HashTables, if the value for the persistent
parameter is set, then the memory allocation for the entered item should be
persistent to i.e. pemalloc() with persistent set to 1.

The following will apply when adding new values into a HashTable for items
that were dynamically allocated :

(a) If the value for the nDataSize parameter is the size of that of a
pointer sizeof(void *), the HashTable API copies the contents of
the pData parameter into the Bucket->pDataPtr member for that data Bucket.
Then it sets the Bucket->pData member to the address of the Bucket->pDataPtr
member for that data Bucket.

(b) If the value for the nDataSize parameter is not equal to sizeof(void *),
the HashTable API allocates new memory for the Bucket->pData member using
the size equivalent to nDataSize and the same value for the persistent flag
set for the target HashTable. The the contents of the pData parameter is
copied into the Bucket->pData member in this newly allocated memory location.
Then the Bucket->pDataPtr member for this Bucket is set to NULL.

Do not worry about the newly allocated memory allocated by the HashTable API;
if the nDataSize parameter was not equal to sizeof(void *), then
during the cleanup process, the Zend API will free the new memory it allocated
during the insert process.

It will also call the destructor function if a valid one was passed when the
HashTable was initialized with zend_hash_init().

In the extension, I have used the p* version of the memory allocation functions
to allow me toggle if there is any need to do so in the future. This will prevent
a massive search and replace effort.

For all the HashTables, I set the intial size to 8 to reduce the looping when
zend_hash_init() is setting up the HashTable pointer to use.