Cache server in 30 lines

This is a cache server that can add, delete and query key/value pairs, with their number limited only by available memory.

We'll use "tree" type, which is a high-performance data structure. For example, with 1,000,000 keys it will take only about 20 comparisons to find any key; and the range search is just one hop. Index is based on a modified AVL/B tree.

Create new "tree" application first, in a new directory (you can name it anything you like):

mkdir -p tree
cd tree

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The mgrg command is a Golf service manager and here it will create a new application named "tree" (it can be different from the directory it's in):

gg -k tree

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Create a source code file "srv.golf":

vi srv.golf

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and copy and paste this:

begin-handler /srv public
    do-once
        new-tree ind process-scope
    end-do-once
    get-param op
    get-param key
    get-param data default-value ""
    if-true op equal "add"
        write-tree ind key (key) value data status st
        if-true st equal GG_ERR_EXIST
            @Key exists [<<print-out key>>]
        else-if
            @Added [<<print-out key>>]
        end-if
    else-if op equal "delete"
        delete-tree ind key (key) value val status st
        if-true st equal GG_ERR_EXIST
            @Not found [<<print-out key>>]
        else-if
            @Deleted, old value was [<<print-out val>>]
        end-if
    else-if op equal "query"
        read-tree ind equal (key) value val status st
        if-true st equal GG_ERR_EXIST
            @Not found, queried [<<print-out key>>]
        else-if
            @Value [<<print-out val>>]
        end-if
    end-if
end-handler

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A service will run as a single process because each operation is handled very fast, even with large number of concurrent requests.

Build a service

gg -q

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Run as service

mgrg -w 1 tree

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The above will start a single server process (-w 1) to serve incoming requests.

Test it

This is a bash test script to insert 3 keys into your cache server, query them, then delete them. Create "test_tree" file:

vi test_tree

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And copy/paste the following:

#Add 3 key/data pairs. Key value is 0,1,2... and data values are "data_0", "data_1", "data_2" etc.
for i in {1..3}; do
   gg -r --req="/srv/op=add/key=$i/data=data_$i" --exec --service --app="/tree" --silent-header
done
echo "Keys added"

#Query all 3 keys and check that values retrieved are the correct ones.
for i in {1..3}; do
   gg -r --req="/srv/op=query/key=$i" --exec --service --app="/tree" --silent-header
done
echo "Keys queried"

#Delete all 3 keys
ERR="0"
for i in {1..3}; do
   gg -r --req="/srv/op=delete/key=$i" --exec --service --app="/tree" --silent-header
done
echo "Keys deleted"

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Make sure it's executable and run it:

chmod +x test_tree
./test_tree

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The result is this:

Added [1]
Added [2]
Added [3]
Keys added
Value [data_1]
Value [data_2]
Value [data_3]
Keys queried
Deleted, old value was [data_1]
Deleted, old value was [data_2]
Deleted, old value was [data_3]
Keys deleted

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