rax.h raxRemove recompression not working as expected (redirect from redis project)

[MEDSMEDS]

in file rax.c, the comment within function raxRemove claims the following:

* Example of case "1". A tree stores the keys "FOO" = 1 and
     * "FOOBAR" = 2:
     *
     *
     * "FOO" -> "BAR" -> [] (2)
     *           (1)
     *
     * After the removal of "FOO" the tree can be compressed as:
     *
     * "FOOBAR" -> [] (2)
     *

However, the logic associated with variable trycompress didn't take compress node into account.
The two predicates if (h->size == 0) and else if (h->size == 1) don't catch the intermediate compress node obviously.

This demo shows the real scenario:

1. insertion of key "foo", value 1.
2. insertion of key "foobar", value 2.
3. insertion of key "foobarzxc", value 3.
4. deletion of key "foobarzxc".
5. deletion of key "foobar".

// after 1/2/3
"foo" -> "bar"=0x7ffc7cbdb69c -> "zxc"=0x7ffc7cbdb64c -> []=0x7ffc7cbdb5fc
// after 4/5
"foo" -> "bar" -> "zxc" -> []=0x7ffc7cbdb5fc

Not "foobarzxc" -> []=0x7ffc7cbdb5fc as expected

Anyway, this only prolongs the recompression and no bug is incurred. @antirez