You are viewing a plain text version of this content. The canonical link for it is here.
Posted to erlang@couchdb.apache.org by David Martin <da...@lymegreen.co.uk> on 2012/11/04 16:44:04 UTC
Using the Erlang view server to Educate in CouchDB
Learning about the Erlang internals of CouchDB is daunting for many.
One of the reasons for this is the difficulty of learning the
intricacies of
the build system and finding your way around the code.
Jan Lehnart has made a very good start with his recent well written post
detailing a
walk through the code that is used during a POST/PUT operation.
Thank you Jan!
I offer another insight into the Erlang world of CouchDB that is very easy
to implement, needs no delving into the codebase or build systems,
yet gives an insight to many of the important concepts used in CouchDB
and Erlang.
This example posted below uses the Erlang (a.k.a native) query server
to illustrate an Erlang solution to the problem of knowing what data is in
a free-form database. (determining "Schemas" in freeform data).
This can also be done in Javascript, but hey! this is about Erlang.
As all clients of a CouchDB database are (in general terms) free to create
JSON structures of an arbitrary form the problem becomes one of finding
Views that are of interest to potential users of the data.
As an illustration, take a police criminal investigation.
All the thousands of contributors to the accumulation of data on the case
use different nomenclature and forms and languages and computer systems to
urgently collate the data in office of Inspector Jacques Clouseau.
Jacques has a schema in mind for his huge police SQL database, but the
urgency
of the case, the Press pressure, the masses of international data pouring
in forces his hand. He says,
"As long as you send in the data in JSON format, I will do the rest! just
send it in to this new CouchDB using Futon in any form you wish."
The database grows at an alarming rate.
Jacques goes to his local.ini file and types the magic words,
[native_query_servers]
erlang = {couch_native_process, start_link, []}
and restarts his CouchDB server.
Then he opens the rapidly growing database and in Futon types the Map
Function
below within the #### lines
###############################################################################
fun({Doc})-> % The view function using The Y-Combinator
%% david m. w. martin 2012 U.K.. david.martin@lymegreen.co.uk
%% use the Y-combinator function for anonymous recursion, thanks Haskell
Curry!
Y = fun(M)->(fun(X) -> X(X) end)(fun (F) -> M(fun(A) -> (F(F))(A) end)
end) end,
%-------------------------------------------
Logging_on = false, %% logging is to couch.log
Recurser = fun (F) ->
%start of inner functions,
%they can only pass 1 argument so we use a tuple
fun
%-------------------------------------------------------------------
({logger,Legend_string,Parms}) ->
case Logging_on of
true-> Log(io_lib:format(Legend_string,Parms));
false->ok
end;
%-------------------------------------------------------------------------------
({Term,Path,Q0}) when is_list(Term)->
%F({logger,"state of Q = ~p",[Q0]}),
lists:foreach(fun (Key) ->
case proplists:get_value(Key,Term,null) of
Value when is_tuple(Value)->
Path1 =[Key|Path],
{Stripped_Value}=Value,
F({Stripped_Value,[Key|Path],Q0}); % recursive call to F
Value when is_list(Value)->
lists:foreach(fun ({Element,Index}) ->
Path1=[ [Index] |[ Key | Path]],
F({Element,Path1,Index}) % recursive call to F
end,lists:zip(Value,lists:seq(0,length(Value)-1)));
Value->
Path1=[Key|Path],
Emit(lists:reverse(Path1),1)
end
end, proplists:get_keys(Term));
%-------------------------------------------------------------------
({Element,Path,Queue}) when is_tuple(Element)->
{Stripped_Value}=Element,
F({Stripped_Value,Path,Queue}); % recursive call to F
%-------------------------------------------------------------------
({Element,Path,Queue})->
Emit(lists:reverse(Path),1)
end %end of inner Functions
%-------------------------------------------------------------------------------
end, % end of Recurser
%% this line calls the Y(Recursor) with in intial parameter
{Doc,[<<"Doc">>],0}
Log(io_lib:format("
## End of Document ####~n~p~n", [ (Y(Recurser))( {Doc,[<<"Doc">>],0} )] ))
end. % end of View fun
################################################################################
and the reduce function
################################################################################
fun(Keys,Values,ReReduce)->
case ReReduce of
true->lists:sum(Values); % it is a ReReduce of Values
false->length(Values) % it is just a reduce of Values
end
end.
################################################################################
The Inspector thanks ben hollis at http://benhollis.net/
for the inspiration to crack JSON using some of his test data below,
modified
to show objects within arrays and arrays within objects.
Test data in JSON form, your _id and _rev will differ.
{
"_id": "61c3f496b9e4c8dc29b95270d9000370",
"_rev": "5-672ef483f9f4fb1386e38bb691442183",
"test": {
"hey": "guy",
"a_number": 243,
"an_object": {
"whoa": "nuts",
"an_array": [
1.0000000000001,
2,
"thr<h1>ee",
{
"whoa": "nuts",
"an_array": [
1,
3.9999999999,
"thr<h1>ee"
]
}
]
},
"awesome": true,
"bogus": false,
"meaning": null,
"japanese": "明日がある。",
"link": "http://jsonview.com",
"notLink": "http://jsonview.com is great"
}
}
This is the form in which CouchDB stores the Documents on disk
and this is the form on which Erlang works internally on JSON documents
{[{<<"_id">>,<<"61c3f496b9e4c8dc29b95270d9000370">>},
{<<"_rev">>,<<"5-672ef483f9f4fb1386e38bb691442183">>},
{<<"test">>,
{[{<<"hey">>,<<"guy">>},
{<<"a_number">>,243},
{<<"an_object">>,
{[{<<"whoa">>,<<"nuts">>},
{<<"an_array">>,
[1.0000000000001,2,<<"thr<h1>ee">>,
{[{<<"whoa">>,<<"nuts">>},
{<<"an_array">>,[1,3.9999999999,<<"thr<h1>ee">>]}]}]}]}},
{<<"awesome">>,true},
{<<"bogus">>,false},
{<<"meaning">>,null},
{<<"japanese">>,
<<230,152,142,230,151,165,227,129,140,227,129,130,227,130,139,227,128,130>>},
{<<"link">>,<<"http://jsonview.com">>},
{<<"notLink">>,<<"http://jsonview.com is great">>}]}}]}
The Inspector tested the map function and reduce function with differing
levels
of grouping on the test data.Then the Inspector found all the relevant data
in the now huge database of clues and was able, using the output, to
construct
Javascript Views that could seek out and collate every last relevant
piece of
data in the database. The case was solved in record time!
The map function allows deep recursion to be performed on each document
in a
database and in order to protect the concurrent running and updating of the
database, (clues are still coming in), the gen_server handling the mapping
may take too long resulting in a message
"Error: timeout
{gen_server,call,
[<0.4612.32>,
{prompt,[<<"map_doc">>,......
This happens on slow machines with very complex document structures.
Increase "os_process_timeout 5000 in default.ini to larger values.
The Erlang view server is very powerful, In fact it can access all the
functionality of CouchDB and all the functions of Erlang.
This is with the proviso that it is called on every document in a database,
and can only recurse using the Y-Combinator.
If you only have one dummy document,
you only call the function once and can thus code like
lists:foreach(fun(X)->
Log(io_lib:format("~p: ~p",[X,ets:info(X)]))
end,ets:all()),
inserted after "end, % end of Recurser"
will give a list of elements like
inet_hosts_byaddr: [{compressed,false},
{memory,286},
{owner,<0.16.0>},
{heir,none},
{name,inet_hosts_byaddr},
{size,0},
{node,'rcouch@127.0.0.1'},
{named_table,true},
{type,bag},
{keypos,3},
{protection,protected}]
ac_tab: [{compressed,false},
{memory,8265},
{owner,<0.7.0>},
{heir,none},
{name,ac_tab},
{size,127},
{node,'rcouch@127.0.0.1'},
{named_table,true},
{type,set},
{keypos,1},
{protection,public}] ....
of (ets:info) on (ets:all) i.e. all ets tables in CouchDB
The Inspector says, "It would be nice for Erlang Views to have their
own ETS table in this list, instead of grabbing {protection,public}
ones for transient use!"
I conclude by saying what Robert Newson would wish me to say,
"This is for your education in Erlang and CouchDB and should not be used
in any
mission critical applications. The Erlang View Server is not sandboxed,
and carefully crafted functions can damage your whole life as you know it".
"As long as you trust everyone that can update design documents, that is
fine"
I hope this is of some use to ESAK's (Earnest Seekers After Knowledge)
into the mysteries of Erlang and its use in CouchDB wherever they may be.
Any improvements, questions or comments will be gratefully received,
David M. W. Martin (davidoccam)
Re: Using the Erlang view server to Educate in CouchDB
Posted by Noah Slater <ns...@apache.org>.
Did we move this anywhere?
In general, is there a plan to syphon off information from this list into a
central location that is easy to browse?
On 7 November 2012 23:59, Jan Lehnardt <ja...@apache.org> wrote:
> Alexander,
>
> good stuff! I’d love to see that in the official docs.
> There’s room for some minor improvements, but overall this is great
> to have documentation! :)
>
> Cheers
> Jan
> --
>
> On Nov 6, 2012, at 03:21 , Alexander Shorin <kx...@gmail.com> wrote:
>
> > David, you're rocks(:
> >
> > By the way, I'd made first steps in documenting Erlang query server
> > [1], thanks Robert for pushing me into the source in previous thread(:
> > It looks a little poorly made for now, I just couldn't figure what
> > also need to write.
> >
> > May I ask you and everyone to help and take a part in making CouchDB
> > Documentation For Great Relax?(:
> >
> > [1]: http://kxepal.iriscouch.com/docs/1.3/queryservers.html#erlang
> > --
> > ,,,^..^,,,
> >
> >
> > On Tue, Nov 6, 2012 at 6:10 AM, david martin
> > <da...@lymegreen.co.uk> wrote:
> >> On 05/11/12 01:43, Kai Griffin wrote:
> >>>
> >>> Thanks for this entertaining & informative post, David. Erlang is a
> >>> totally foreign language to me,
> >>
> >>
> >>> but I joined this new list hoping to rectify that situation over time,
> >>
> >>
> >>> and this is exactly the kind of stuff I'd like to archive for future
> >>> reference when I get some time to wade into it properly.
> >>
> >>
> >>> I think experimenting with the native query server is potentially a
> great
> >>> way to learn (and perhaps destroy a few databases along the way...).
> >>> Cheers,
> >>> Kai
> >>
> >>
> >> I LIKE YOUR STYLE KAI, ya!
> >> nice to see you are watching,ya!
> >> and learning and proselytising , ya!.
> >> Erlang and OTP rules, ya!
> >> i like your cool tunes, ya!,
> >> I think we can rule-ok, ya!
> >> Time is of the essence, ya!,
> >> is'ism is of the meaning of what really is ya!
> >> to rectify the def-is-ie-ncy, ya!,
> >> “I AM THAT I AM.”,ya!
> >> I'm sure you will, ya!
> >> davidoccam will help you , ya!
> >>
> >>
> >> All correspondence will be pulped ya!.
> >>
>
>
--
NS
Re: Using the Erlang view server to Educate in CouchDB
Posted by Jan Lehnardt <ja...@apache.org>.
Alexander,
good stuff! I’d love to see that in the official docs.
There’s room for some minor improvements, but overall this is great
to have documentation! :)
Cheers
Jan
--
On Nov 6, 2012, at 03:21 , Alexander Shorin <kx...@gmail.com> wrote:
> David, you're rocks(:
>
> By the way, I'd made first steps in documenting Erlang query server
> [1], thanks Robert for pushing me into the source in previous thread(:
> It looks a little poorly made for now, I just couldn't figure what
> also need to write.
>
> May I ask you and everyone to help and take a part in making CouchDB
> Documentation For Great Relax?(:
>
> [1]: http://kxepal.iriscouch.com/docs/1.3/queryservers.html#erlang
> --
> ,,,^..^,,,
>
>
> On Tue, Nov 6, 2012 at 6:10 AM, david martin
> <da...@lymegreen.co.uk> wrote:
>> On 05/11/12 01:43, Kai Griffin wrote:
>>>
>>> Thanks for this entertaining & informative post, David. Erlang is a
>>> totally foreign language to me,
>>
>>
>>> but I joined this new list hoping to rectify that situation over time,
>>
>>
>>> and this is exactly the kind of stuff I'd like to archive for future
>>> reference when I get some time to wade into it properly.
>>
>>
>>> I think experimenting with the native query server is potentially a great
>>> way to learn (and perhaps destroy a few databases along the way...).
>>> Cheers,
>>> Kai
>>
>>
>> I LIKE YOUR STYLE KAI, ya!
>> nice to see you are watching,ya!
>> and learning and proselytising , ya!.
>> Erlang and OTP rules, ya!
>> i like your cool tunes, ya!,
>> I think we can rule-ok, ya!
>> Time is of the essence, ya!,
>> is'ism is of the meaning of what really is ya!
>> to rectify the def-is-ie-ncy, ya!,
>> “I AM THAT I AM.”,ya!
>> I'm sure you will, ya!
>> davidoccam will help you , ya!
>>
>>
>> All correspondence will be pulped ya!.
>>
Re: Using the Erlang view server to Educate in CouchDB
Posted by Alexander Shorin <kx...@gmail.com>.
David, you're rocks(:
By the way, I'd made first steps in documenting Erlang query server
[1], thanks Robert for pushing me into the source in previous thread(:
It looks a little poorly made for now, I just couldn't figure what
also need to write.
May I ask you and everyone to help and take a part in making CouchDB
Documentation For Great Relax?(:
[1]: http://kxepal.iriscouch.com/docs/1.3/queryservers.html#erlang
--
,,,^..^,,,
On Tue, Nov 6, 2012 at 6:10 AM, david martin
<da...@lymegreen.co.uk> wrote:
> On 05/11/12 01:43, Kai Griffin wrote:
>>
>> Thanks for this entertaining & informative post, David. Erlang is a
>> totally foreign language to me,
>
>
>> but I joined this new list hoping to rectify that situation over time,
>
>
>> and this is exactly the kind of stuff I'd like to archive for future
>> reference when I get some time to wade into it properly.
>
>
>> I think experimenting with the native query server is potentially a great
>> way to learn (and perhaps destroy a few databases along the way...).
>> Cheers,
>> Kai
>
>
> I LIKE YOUR STYLE KAI, ya!
> nice to see you are watching,ya!
> and learning and proselytising , ya!.
> Erlang and OTP rules, ya!
> i like your cool tunes, ya!,
> I think we can rule-ok, ya!
> Time is of the essence, ya!,
> is'ism is of the meaning of what really is ya!
> to rectify the def-is-ie-ncy, ya!,
> “I AM THAT I AM.”,ya!
> I'm sure you will, ya!
> davidoccam will help you , ya!
>
>
> All correspondence will be pulped ya!.
>
Re: Using the Erlang view server to Educate in CouchDB
Posted by Kai Griffin <ka...@resourceandrevenue.com>.
On 06/11/2012 03:10, david martin wrote:
> On 05/11/12 01:43, Kai Griffin wrote:
>> Thanks for this entertaining & informative post, David. Erlang is a
>> totally foreign language to me,
>
>> but I joined this new list hoping to rectify that situation over time,
>
>> and this is exactly the kind of stuff I'd like to archive for future
>> reference when I get some time to wade into it properly.
>
>> I think experimenting with the native query server is potentially a
>> great way to learn (and perhaps destroy a few databases along the
>> way...).
>> Cheers,
>> Kai
>
> I LIKE YOUR STYLE KAI, ya!
> nice to see you are watching,ya!
> and learning and proselytising , ya!.
> Erlang and OTP rules, ya!
> i like your cool tunes, ya!,
> I think we can rule-ok, ya!
> Time is of the essence, ya!,
> is'ism is of the meaning of what really is ya!
> to rectify the def-is-ie-ncy, ya!,
> “I AM THAT I AM.”,ya!
> I'm sure you will, ya!
> davidoccam will help you , ya!
>
>
> All correspondence will be pulped ya!.
>
>
>
LOL. Was that Erlang code... or Rastafarian toasting? (feel free to pulp)
Re: Using the Erlang view server to Educate in CouchDB
Posted by david martin <da...@lymegreen.co.uk>.
On 05/11/12 01:43, Kai Griffin wrote:
> Thanks for this entertaining & informative post, David. Erlang is a totally foreign language to me,
> but I joined this new list hoping to rectify that situation over time,
> and this is exactly the kind of stuff I'd like to archive for future reference when I get some time to wade into it properly.
> I think experimenting with the native query server is potentially a great way to learn (and perhaps destroy a few databases along the way...).
> Cheers,
> Kai
I LIKE YOUR STYLE KAI, ya!
nice to see you are watching,ya!
and learning and proselytising , ya!.
Erlang and OTP rules, ya!
i like your cool tunes, ya!,
I think we can rule-ok, ya!
Time is of the essence, ya!,
is'ism is of the meaning of what really is ya!
to rectify the def-is-ie-ncy, ya!,
“I AM THAT I AM.”,ya!
I'm sure you will, ya!
davidoccam will help you , ya!
All correspondence will be pulped ya!.
Re: Using the Erlang view server to Educate in CouchDB
Posted by Kai Griffin <ka...@resourceandrevenue.com>.
Thanks for this entertaining & informative post, David. Erlang is a
totally foreign language to me, but I joined this new list hoping to
rectify that situation over time, and this is exactly the kind of stuff
I'd like to archive for future reference when I get some time to wade
into it properly. I think experimenting with the native query server is
potentially a great way to learn (and perhaps destroy a few databases
along the way...).
Cheers,
Kai
On 04/11/2012 16:44, David Martin wrote:
> Learning about the Erlang internals of CouchDB is daunting for many.
>
> One of the reasons for this is the difficulty of learning the
> intricacies of
> the build system and finding your way around the code.
>
> Jan Lehnart has made a very good start with his recent well written
> post detailing a
> walk through the code that is used during a POST/PUT operation.
>
> Thank you Jan!
>
> I offer another insight into the Erlang world of CouchDB that is very
> easy
> to implement, needs no delving into the codebase or build systems,
> yet gives an insight to many of the important concepts used in CouchDB
> and Erlang.
>
> This example posted below uses the Erlang (a.k.a native) query server
> to illustrate an Erlang solution to the problem of knowing what data
> is in
> a free-form database. (determining "Schemas" in freeform data).
>
> This can also be done in Javascript, but hey! this is about Erlang.
>
> As all clients of a CouchDB database are (in general terms) free to
> create
> JSON structures of an arbitrary form the problem becomes one of finding
> Views that are of interest to potential users of the data.
>
> As an illustration, take a police criminal investigation.
> All the thousands of contributors to the accumulation of data on the case
> use different nomenclature and forms and languages and computer
> systems to
> urgently collate the data in office of Inspector Jacques Clouseau.
>
> Jacques has a schema in mind for his huge police SQL database, but the
> urgency
> of the case, the Press pressure, the masses of international data pouring
> in forces his hand. He says,
> "As long as you send in the data in JSON format, I will do the rest! just
> send it in to this new CouchDB using Futon in any form you wish."
>
> The database grows at an alarming rate.
> Jacques goes to his local.ini file and types the magic words,
>
> [native_query_servers]
> erlang = {couch_native_process, start_link, []}
>
> and restarts his CouchDB server.
>
> Then he opens the rapidly growing database and in Futon types the Map
> Function
> below within the #### lines
>
> ###############################################################################
>
> fun({Doc})-> % The view function using The Y-Combinator
>
> %% david m. w. martin 2012 U.K.. david.martin@lymegreen.co.uk
> %% use the Y-combinator function for anonymous recursion, thanks
> Haskell Curry!
>
> Y = fun(M)->(fun(X) -> X(X) end)(fun (F) -> M(fun(A) -> (F(F))(A) end)
> end) end,
> %-------------------------------------------
> Logging_on = false, %% logging is to couch.log
>
> Recurser = fun (F) ->
>
> %start of inner functions,
> %they can only pass 1 argument so we use a tuple
>
> fun
> %-------------------------------------------------------------------
>
> ({logger,Legend_string,Parms}) ->
> case Logging_on of
> true-> Log(io_lib:format(Legend_string,Parms));
> false->ok
> end;
> %-------------------------------------------------------------------------------
>
> ({Term,Path,Q0}) when is_list(Term)->
> %F({logger,"state of Q = ~p",[Q0]}),
> lists:foreach(fun (Key) ->
> case proplists:get_value(Key,Term,null) of
>
> Value when is_tuple(Value)->
> Path1 =[Key|Path],
> {Stripped_Value}=Value,
> F({Stripped_Value,[Key|Path],Q0}); % recursive call to F
> Value when is_list(Value)->
> lists:foreach(fun ({Element,Index}) ->
> Path1=[ [Index] |[ Key | Path]],
> F({Element,Path1,Index}) % recursive call to F
> end,lists:zip(Value,lists:seq(0,length(Value)-1)));
>
> Value->
> Path1=[Key|Path],
> Emit(lists:reverse(Path1),1)
>
> end
> end, proplists:get_keys(Term));
> %-------------------------------------------------------------------
> ({Element,Path,Queue}) when is_tuple(Element)->
> {Stripped_Value}=Element,
> F({Stripped_Value,Path,Queue}); % recursive call to F
> %-------------------------------------------------------------------
> ({Element,Path,Queue})->
> Emit(lists:reverse(Path),1)
>
> end %end of inner Functions
> %-------------------------------------------------------------------------------
>
> end, % end of Recurser
> %% this line calls the Y(Recursor) with in intial parameter
> {Doc,[<<"Doc">>],0}
> Log(io_lib:format("
> ## End of Document ####~n~p~n", [ (Y(Recurser))( {Doc,[<<"Doc">>],0}
> )] ))
>
> end. % end of View fun
>
> ################################################################################
>
>
> and the reduce function
>
> ################################################################################
>
> fun(Keys,Values,ReReduce)->
> case ReReduce of
> true->lists:sum(Values); % it is a ReReduce of Values
> false->length(Values) % it is just a reduce of Values
> end
> end.
> ################################################################################
>
>
> The Inspector thanks ben hollis at http://benhollis.net/
> for the inspiration to crack JSON using some of his test data below,
> modified
> to show objects within arrays and arrays within objects.
>
> Test data in JSON form, your _id and _rev will differ.
>
> {
> "_id": "61c3f496b9e4c8dc29b95270d9000370",
> "_rev": "5-672ef483f9f4fb1386e38bb691442183",
> "test": {
> "hey": "guy",
> "a_number": 243,
> "an_object": {
> "whoa": "nuts",
> "an_array": [
> 1.0000000000001,
> 2,
> "thr<h1>ee",
> {
> "whoa": "nuts",
> "an_array": [
> 1,
> 3.9999999999,
> "thr<h1>ee"
> ]
> }
> ]
> },
> "awesome": true,
> "bogus": false,
> "meaning": null,
> "japanese": "明日がある。",
> "link": "http://jsonview.com",
> "notLink": "http://jsonview.com is great"
> }
> }
>
> This is the form in which CouchDB stores the Documents on disk
> and this is the form on which Erlang works internally on JSON documents
>
> {[{<<"_id">>,<<"61c3f496b9e4c8dc29b95270d9000370">>},
> {<<"_rev">>,<<"5-672ef483f9f4fb1386e38bb691442183">>},
> {<<"test">>,
> {[{<<"hey">>,<<"guy">>},
> {<<"a_number">>,243},
> {<<"an_object">>,
> {[{<<"whoa">>,<<"nuts">>},
> {<<"an_array">>,
> [1.0000000000001,2,<<"thr<h1>ee">>,
> {[{<<"whoa">>,<<"nuts">>},
> {<<"an_array">>,[1,3.9999999999,<<"thr<h1>ee">>]}]}]}]}},
> {<<"awesome">>,true},
> {<<"bogus">>,false},
> {<<"meaning">>,null},
> {<<"japanese">>,
> <<230,152,142,230,151,165,227,129,140,227,129,130,227,130,139,227,128,130>>},
>
> {<<"link">>,<<"http://jsonview.com">>},
> {<<"notLink">>,<<"http://jsonview.com is great">>}]}}]}
>
> The Inspector tested the map function and reduce function with
> differing levels
> of grouping on the test data.Then the Inspector found all the relevant
> data
> in the now huge database of clues and was able, using the output, to
> construct
> Javascript Views that could seek out and collate every last relevant
> piece of
> data in the database. The case was solved in record time!
>
> The map function allows deep recursion to be performed on each
> document in a
> database and in order to protect the concurrent running and updating
> of the
> database, (clues are still coming in), the gen_server handling the
> mapping
> may take too long resulting in a message
>
> "Error: timeout
> {gen_server,call,
> [<0.4612.32>,
> {prompt,[<<"map_doc">>,......
>
> This happens on slow machines with very complex document structures.
>
> Increase "os_process_timeout 5000 in default.ini to larger values.
>
> The Erlang view server is very powerful, In fact it can access all the
> functionality of CouchDB and all the functions of Erlang.
> This is with the proviso that it is called on every document in a
> database,
> and can only recurse using the Y-Combinator.
>
> If you only have one dummy document,
> you only call the function once and can thus code like
>
> lists:foreach(fun(X)->
> Log(io_lib:format("~p: ~p",[X,ets:info(X)]))
> end,ets:all()),
>
> inserted after "end, % end of Recurser"
>
> will give a list of elements like
>
> inet_hosts_byaddr: [{compressed,false},
> {memory,286},
> {owner,<0.16.0>},
> {heir,none},
> {name,inet_hosts_byaddr},
> {size,0},
> {node,'rcouch@127.0.0.1'},
> {named_table,true},
> {type,bag},
> {keypos,3},
> {protection,protected}]
>
> ac_tab: [{compressed,false},
> {memory,8265},
> {owner,<0.7.0>},
> {heir,none},
> {name,ac_tab},
> {size,127},
> {node,'rcouch@127.0.0.1'},
> {named_table,true},
> {type,set},
> {keypos,1},
> {protection,public}] ....
>
> of (ets:info) on (ets:all) i.e. all ets tables in CouchDB
>
> The Inspector says, "It would be nice for Erlang Views to have their
> own ETS table in this list, instead of grabbing {protection,public}
> ones for transient use!"
>
> I conclude by saying what Robert Newson would wish me to say,
> "This is for your education in Erlang and CouchDB and should not be
> used in any
> mission critical applications. The Erlang View Server is not sandboxed,
> and carefully crafted functions can damage your whole life as you know
> it".
> "As long as you trust everyone that can update design documents, that
> is fine"
>
> I hope this is of some use to ESAK's (Earnest Seekers After Knowledge)
> into the mysteries of Erlang and its use in CouchDB wherever they may be.
>
> Any improvements, questions or comments will be gratefully received,
>
> David M. W. Martin (davidoccam)
>
>
>
>
>