/**
@page working_with_memory Working with Memory and Performance

@tableofcontents

@section ww_mem_constant Constant Memory Mode

By default libxlsxwriter holds all cell data in memory. This is to allow
non-sequential data storage and also to allow future features where formatting
is applied separately from the data.

The effect of this is that for large files libxlsxwriter can consume a lot of
memory.

Fortunately, this memory usage can be reduced almost completely by using
workbook_new_opt() and the lxw_workbook_options `constant_memory` property:

@dontinclude constant_memory.c
@skipline include
@until    return
@skipline }

This optimization works by flushing each row after a subsequent row is written.
In this way the largest amount of data held in memory for a worksheet is the
amount of data required to hold a single row of data.

If required, this memory usage can be reduced even more by setting
`LXW_COL_MAX` in worksheet.c from 16384 down to a value that matches the
maximum column that is likely to be encountered.

The trade-off when using `constant_memory` mode is that data must be added
sequentially in row order and you won't be able to take advantage of any
functions that manipulate cell data after it is written. For example:

- In `constant_memory` mode `worksheet_set_row()` can only be used when
  writing data to the current row. This has an additional knock on effect that
  images won't scale properly over row heights adjusted with
  `%worksheet_set_row()`.

- A merged range set with `worksheet_merge_range()` can only be applied to the
  current row (which in general isn't very useful).

@subsection ww_mem_row_order Row Column Order

Since each new row flushes the previous row, data must be written in sequential
row order when `constant_memory` mode is on:

@code
    lxw_workbook  *workbook  = workbook_new_opt("constant_memory.xlsx", &options);
    ...

    // !! Don't use "column x row" order in 'constant_memory' mode. Only
    //    the first column of data will be written.
    for (col = 0; col < max_col; col++) {
        for (row = 0; row < max_row; row++) {
            worksheet_write_number(worksheet, row, col, 123.45, NULL);
        }
    }
 @endcode


@subsection ww_mem_temp Constant memory mode and the /tmp directory

The libxlsxwriter library uses temporary files stored in the system `/tmp`
directory prior to creating the final xlsx file. In `constant_memory` mode the
library uses additional temporary file storage for worksheet data. This can
lead to an issue on OSes that map the `/tmp` directory into memory since it is
possible for a libxlsxwriter application to consume the "system" memory via
disk usage even though the "process" memory remains constant.

This is generally only an issue with embedded Linux systems with limited
amounts of system memory. In these cases you should use an alternative
temporary file location by using the `tmpdir` option of #lxw_workbook_options
and workbook_new_opt().


@subsection ww_mem_inline_strings Inline strings

Another optimization that is used to reduce memory usage in `constant_memory`
mode is that cell strings aren't stored in an Excel structure call "shared
strings" and instead are written "in-line".

This is a documented Excel feature that is supported by most spreadsheet
applications. However, it isn't supported by some some spreadsheet viewer
applications. Also, the size of the output file can increase by 20%-100%
depending on the amount of repeated string data.


@section ww_mem_performance Performance

Currently the library is optimized but not highly optimized. Also, the library
is currently single threaded.

Next: @ref working_with_macros


*/
