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Handle empty tables in concurrency support for MySQL.

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When the table is empty we get nil for min and max values of the id column.
In that case we don't compute a set of ranges and “cancel” concurrency
support for the empty table.

Fixes #596.
This commit is contained in:
Dimitri Fontaine 2017-07-18 13:35:01 +02:00
parent b1fa3aec3c
commit d37ad27754
1 changed files with 24 additions and 18 deletions
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42
src/sources/mysql/mysql.lisp
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@ -58,25 +58,31 @@
(sql (format nil "select min(`~a`), max(`~a`) from `~a`" (sql (format nil "select min(`~a`), max(`~a`) from `~a`"
col col (table-source-name (source mysql))))) col col (table-source-name (source mysql)))))
(destructuring-bind (min max) (destructuring-bind (min max)
(mapcar #'parse-integer (first (mysql-query sql))) (let ((result (first (mysql-query sql))))
;; result is (min max), or (nil nil) if table is empty
(if (or (null (first result))
(null (second result)))
result
(mapcar #'parse-integer result)))
;; generate a list of ranges from min to max ;; generate a list of ranges from min to max
(let ((range-list (split-range min max *rows-per-range*))) (when (and min max)
(unless (< (length range-list) concurrency) (let ((range-list (split-range min max *rows-per-range*)))
;; affect those ranges to each reader, we have CONCURRENCY (unless (< (length range-list) concurrency)
;; of them ;; affect those ranges to each reader, we have CONCURRENCY
(let ((partitions (distribute range-list concurrency))) ;; of them
(loop :for part :in partitions :collect (let ((partitions (distribute range-list concurrency)))
(make-instance 'copy-mysql (loop :for part :in partitions :collect
:source-db (clone-connection (make-instance 'copy-mysql
(source-db mysql)) :source-db (clone-connection
:target-db (target-db mysql) (source-db mysql))
:source (source mysql) :target-db (target-db mysql)
:target (target mysql) :source (source mysql)
:fields (fields mysql) :target (target mysql)
:columns (columns mysql) :fields (fields mysql)
:transforms (transforms mysql) :columns (columns mysql)
:encoding (encoding mysql) :transforms (transforms mysql)
:range-list (cons col part))))))))))))) :encoding (encoding mysql)
:range-list (cons col part))))))))))))))
(defmacro with-encoding-handler (&body forms) (defmacro with-encoding-handler (&body forms)
`(handler-bind `(handler-bind