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https://github.com/m00natic/vlfi

View Large Files in Emacs
https://github.com/m00natic/vlfi

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View Large Files in Emacs

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README 

        
* View Large Files



Emacs minor mode that allows viewing, editing, searching and comparing

large files in batches, trading memory for processor time.  Batch size

can be adjusted on the fly and bounds the memory that is to be used

for operations on the file.  This way multiple large files (like

terabytes or whatever) can be instantly and simultaneously accessed

without swapping and degraded performance.



This is development version of the GNU ELPA [[https://elpa.gnu.org/packages/vlf.html][VLF]] package.  Here's what

it offers in a nutshell:



- automatic adjustment of batch size for optimal performance and

  responsiveness

- regular expression search and replace over whole file

- [[http://www.emacswiki.org/emacs/OccurMode][Occur]] like indexing

- by batch [[http://www.emacswiki.org/emacs/EdiffMode][Ediff]] comparison

- automatic scrolling of batches

- chunk editing (save is immediate if size hasn't changed, done in

  constant memory determined by current batch size otherwise)

- options to jump to beginning, end or arbitrary file chunk

- proper dealing with multibyte encodings

- smooth integration with [[http://www.emacswiki.org/emacs/HexlMode][hexl-mode]], just turn it on and the HEX

  editing will work in batches just the same

- works with [[http://www.emacswiki.org/emacs/TrampMode][TRAMP]] so accessing network files is fine and quick

- newly added content is acknowledged if file has changed size

  meanwhile

- as it's a minor mode, font locking and functionality of the

  respective major mode and other minor modes is also present

- can be added as option to automatically open large files



GNU Emacs 23 and 24 are supported.



* Overview and tips



M-x vlf PATH-TO-FILE



** Unicode



Emacs' Unicode support is leveraged so you'll not see bare bytes but

characters decoded as if file is normally opened.  This holds for

editing, search, indexing and comparison.



** 32-bit GNU Emacs



Regular Emacs integers are used, so if you use 32-bit Emacs without

bignum support, *VLF* will not work with files over 512 MB (maximum

integer value).



* Detail usage



** Applicability



To have *vlf* offered as choice when opening large files:



#+BEGIN_SRC emacs-lisp

  (require 'vlf-setup)

#+END_SRC



You can control when *vlf-mode* is invoked or offered with the

*vlf-application* customization option.  By default it will offer

*VLF* when opening large files.  There are also options to never use

it (you can still call *vlf* command explicitly); to use it without

asking for large files or to invoke it on all files.  Here's example

setup such that *vlf-mode* automatically launches for large files:



#+BEGIN_SRC emacs-lisp

  (custom-set-variables

   '(vlf-application 'dont-ask))

#+END_SRC



*** Disable for specific mode



To disable automatic usage of *VLF* for a major mode, add it to

*vlf-forbidden-modes-list*.



*** Disable for specific function



To disable automatic usage of *VLF* for a function, for example named

*func* defined in file *file.el*:



#+BEGIN_SRC emacs-lisp

  (vlf-disable-for-function func "file")

#+END_SRC



** Keymap



All *VLF* operations are grouped under the *C-c C-v* prefix by

default.  Here's example how to add another prefix (*C-x v*):



#+BEGIN_SRC emacs-lisp

  (eval-after-load "vlf"

    '(define-key vlf-prefix-map "\C-xv" vlf-mode-map))

#+END_SRC



** Overall position indicators



To see which part of the file is currently visited and how many

batches there are in overall (using the current batch size), look at

the VLF section in the mode line, file size is also there.



** Batch size control



By default *VLF* gathers statistics over how primitive operations

perform over file and gradually adjusts batch size for better user

experience.  Operations involving multiple batches are tuned more

adventurously.  Overall the more jumping around, searching, indexing,

the better performance should get.



The *vlf-tune-max* option specifies maximum size in bytes a batch

could eventually get while tuning.



Profiling and tuning can be disabled by:



#+BEGIN_SRC emacs-lisp

  (custom-set-variables

     '(vlf-tune-enabled nil))

#+END_SRC



Or set *vlf-tune-enabled* to '*stats* to profile but not change batch

size.



Use *M-x vlf-set-batch-size* to change batch size and update chunk

immediately.  Default size offered is the best according to tune

statistics so far.



*C-c C-v +* and *C-c C-v -* control current batch size by factors

of 2.



** Move around



Scrolling automatically triggers move to previous or next chunk at the

beginning or end respectively of the current one.



*C-c C-v n* and *C-c C-v p* move batch by batch.  With positive

prefix argument they move prefix number of batches.  With negative -

append prefix number of batches.



*C-c C-v SPC* displays batch starting from current point.



*C-c C-v [* and *C-c C-v ]* take you to the beginning and end of file

respectively.



*C-c C-v j* jumps to particular batch number.



** Follow point



Continuous chunk recenter around point in current buffer can be

toggled with *C-c C-v f*.



** Search and/or replace whole file



*C-c C-v s* and *C-c C-v r* search forward and backward respectively

over the whole file, batch by batch.  *C-c C-v %* does search and

query replace saving intermediate changes.



** Occur over whole file



*C-c C-v o* builds index over whole file for given regular expression

just like *M-x occur*.  Note that even if you prematurely stop it with

*C-g*, it will still show what's found so far.



Result buffer uses *vlf-occur-mode* which allows to optionally open

new *VLF* buffer on jump to match (using *C-u* before hitting RET or

*o*), thus having multiple simultaneous views of the same file.  Also

results can be serialized to file for later reuse.



** Jump to line



*C-c C-v l* jumps to given line in file.  With negative argument,

lines are counted from the end of file.



** Edit and save



If editing doesn't change size of the chunk, only this chunk is saved.

Otherwise the remaining part of the file is adjusted batch by batch.

*vlf-save-in-place* customization option controls if temporary file

should be used in such case.



** By batch Ediff



Use *M-x vlf-ediff-files* and *M-x vlf-ediff-buffers* to compare

files/buffers batch by batch (batch size is queried in case of files

or taken from the first buffer in case of buffers).  Moving after the

last difference in current chunk searches for following one with

difference.  The other way around if looking for difference before the

first one.



* Extend



** Move hooks



A couple of hooks are run whenever updating chunk:

*vlf-before-chunk-update-hook* and *vlf-after-chunk-update-hook*.



** Batch move hooks



Some operations may trigger multiple chunk moves.  There are a couple

of hooks that run in such cases: *vlf-before-batch-functions* and

*vlf-after-batch-functions*.  They are passed one argument which

specifies type of operation that runs.  Possible values are the

symbols: *write*, *ediff*, *occur*, *search* and *goto-line*.