Implement support for non-btree indexes (e.g. MySQL spatial keys).

When pgloader fetches the index list from a source database, it doesn't
fetch information about access methods for the indexes: I don't even know if
the overlap in between index access methods from one RDMBS to another covers
more than just btree...

It could happen that MySQL indexes a "geometry" column tho. This datatype is
converted automatically to "point" by pgloader, which is good. But the index
creation would fail with the following error message:

  Database error 42704: data type point has no default operator class for access method "btree"

In this patch when setting up the target schema we issue a PostgreSQL
catalog query to dynamically list those datatypes without btree support and
fetch their opclasses, with an hard-coded preference to GiST, then GIN, so
as to be able to automatically use the proper access method when btree isn't
available. And now pgloader transparently issues the proper statement:

  CREATE INDEX idx_168468_idx_location ON pagila.address USING gist(location);

Currently this exploration is limited to indexes with a single column. To
implement the general case we would need a more complex lookup: we would
have to find the intersection of all the supported access methods for all
involved columns.

Of course we might need to do that someday. One step at a time is plenty
good enough tho.

src/package.lisp

@@ -71,6 +71,7 @@
 
            #:catalog-name
            #:catalog-schema-list
+           #:catalog-types-without-btree
 
            #:schema-name
            #:schema-catalog
@@ -410,6 +411,7 @@
 
            ;; postgresql identifiers
 	   #:list-reserved-keywords
+           #:list-typenames-without-btree-support
 
            ;; postgresql user provided gucs
            #:sanitize-user-gucs

src/pgsql/connection.lisp

@@ -338,6 +338,29 @@
 ;;;
 ;;; PostgreSQL version specific support, that we get once connected
 ;;;
+(defun list-typenames-without-btree-support ()
+  "Fetch PostgresQL data types without btree support, so that it's possible
+   to later CREATE INDEX ... ON ... USING gist(...), or even something else
+   than gist. "
+  (loop :for (typename access-methods) :in
+     (pomo:query "
+select typname,
+       array_agg(amname order by amname <> 'gist', amname <> 'gin')
+  from pg_type
+       join pg_opclass on pg_opclass.opcintype = pg_type.oid
+       join pg_am on pg_am.oid = pg_opclass.opcmethod
+ where substring(typname from 1 for 1) <> '_'
+       and not exists
+       (
+         select amname
+           from pg_am am
+                join pg_opclass c on am.oid = c.opcmethod
+                join pg_type t on c.opcintype = t.oid
+          where amname = 'btree' and t.oid = pg_type.oid
+       )
+group by typname;")
+     :collect (cons typename access-methods)))
+
 (defun list-reserved-keywords (pgconn)
   "Connect to PostgreSQL DBNAME and fetch reserved keywords."
   (handler-case

src/pgsql/pgsql-ddl.lisp

@@ -153,7 +153,8 @@
                          (build-identifier "_"
                                            "idx"
                                            (table-oid (index-table index))
-                                           (index-name index)))))
+                                           (index-name index))))
+         (access-method (index-access-method index)))
     (cond
       ((or (index-primary index)
            (and (index-condef index) (index-unique index)))
@@ -185,10 +186,11 @@
       (t
        (or (index-sql index)
            (format stream
-                   "CREATE~:[~; UNIQUE~] INDEX ~a ON ~a (~{~a~^, ~})~@[ WHERE ~a~];"
+                   "CREATE~:[~; UNIQUE~] INDEX ~a ON ~a ~@[USING ~a~](~{~a~^, ~})~@[ WHERE ~a~];"
                    (index-unique index)
                    index-name
                    (format-table-name table)
+                   access-method
                    (index-columns index)
                    (index-filter index)))))))
 
@@ -214,6 +216,28 @@
            (format stream "DROP INDEX~:[~; IF EXISTS~] ~@[~s.~]~s~@[ CASCADE~];"
                    if-exists schema-name index-name cascade)))))
 
+(defun index-access-method (index)
+  "Compute PostgreSQL access method for index. If defaults to btree, but
+  some types such as POINTS or BOX have no support for btree. If a MySQL
+  point column has an index in MySQL, then create a GiST index for it in
+  PostgreSQL."
+  (when (= 1 (length (index-columns index)))
+    ;; we only process single-index columns at the moment, which is a simpler
+    ;; problem space and usefull enough to get started.
+    (let* ((idx-cols   (index-columns index))
+           (tbl-cols   (table-column-list (index-table index)))
+           (idx-types  (loop :for idx-col :in idx-cols
+                          :collect (column-type-name
+                                    (find idx-col tbl-cols
+                                          :test #'string-equal
+                                          :key #'column-name))))
+           (nobtree (catalog-types-without-btree
+                     (schema-catalog (table-schema (index-table index))))))
+      (let* ((idx-type (first idx-types))
+             (method   (cdr (assoc idx-type nobtree :test #'string=))))
+        (when method
+          (aref method 0))))))
+
 
 ;;;
 ;;; Foreign Keys

src/sources/common/db-methods.lisp

@@ -27,6 +27,9 @@
   (log-message :notice "Prepare PostgreSQL database.")
 
   (with-pgsql-transaction (:pgconn (target-db copy))
+    (setf (catalog-types-without-btree catalog)
+          (list-typenames-without-btree-support))
+
     (when create-schemas
       (with-stats-collection ("Create Schemas" :section :pre
                                                :use-result-as-read t

src/utils/catalog.lisp

@@ -42,7 +42,7 @@
 ;;; Column structures details depend on the specific source type and are
 ;;; implemented in each source separately.
 ;;;
-(defstruct catalog name schema-list)
+(defstruct catalog name schema-list types-without-btree)
 (defstruct schema source-name name catalog table-list view-list)
 (defstruct table source-name name schema oid comment storage-parameter-list
            ;; field is for SOURCE