Jak opravit poškozený strom MPTT (vnořená sada) v databázi pomocí SQL?

Zde je to, co jsem upravil z odpovědi @Lieven, včetně zpětné vazby od zde pro lepší výkon:

DROP PROCEDURE IF EXISTS tree_recover;

DELIMITER //

CREATE PROCEDURE tree_recover ()
MODIFIES SQL DATA
BEGIN

    DECLARE currentId, currentParentId  CHAR(36);
    DECLARE currentLeft                 INT;
    DECLARE startId                     INT DEFAULT 1;

    # Determines the max size for MEMORY tables.
    SET max_heap_table_size = 1024 * 1024 * 512;

    START TRANSACTION;

    # Temporary MEMORY table to do all the heavy lifting in,
    # otherwise performance is simply abysmal.
    CREATE TABLE `tmp_tree` (
        `id`        char(36) NOT NULL DEFAULT '',
        `parent_id` char(36)          DEFAULT NULL,
        `lft`       int(11)  unsigned DEFAULT NULL,
        `rght`      int(11)  unsigned DEFAULT NULL,
        PRIMARY KEY      (`id`),
        INDEX USING HASH (`parent_id`),
        INDEX USING HASH (`lft`),
        INDEX USING HASH (`rght`)
    ) ENGINE = MEMORY
    SELECT `id`,
           `parent_id`,
           `lft`,
           `rght`
    FROM   `tree`;

    # Leveling the playing field.
    UPDATE  `tmp_tree`
    SET     `lft`  = NULL,
            `rght` = NULL;

    # Establishing starting numbers for all root elements.
    WHILE EXISTS (SELECT * FROM `tmp_tree` WHERE `parent_id` IS NULL AND `lft` IS NULL AND `rght` IS NULL LIMIT 1) DO

        UPDATE `tmp_tree`
        SET    `lft`  = startId,
               `rght` = startId + 1
        WHERE  `parent_id` IS NULL
          AND  `lft`       IS NULL
          AND  `rght`      IS NULL
        LIMIT  1;

        SET startId = startId + 2;

    END WHILE;

    # Switching the indexes for the lft/rght columns to B-Trees to speed up the next section, which uses range queries.
    DROP INDEX `lft`  ON `tmp_tree`;
    DROP INDEX `rght` ON `tmp_tree`;
    CREATE INDEX `lft`  USING BTREE ON `tmp_tree` (`lft`);
    CREATE INDEX `rght` USING BTREE ON `tmp_tree` (`rght`);

    # Numbering all child elements
    WHILE EXISTS (SELECT * FROM `tmp_tree` WHERE `lft` IS NULL LIMIT 1) DO

        # Picking an unprocessed element which has a processed parent.
        SELECT     `tmp_tree`.`id`
          INTO     currentId
        FROM       `tmp_tree`
        INNER JOIN `tmp_tree` AS `parents`
                ON `tmp_tree`.`parent_id` = `parents`.`id`
        WHERE      `tmp_tree`.`lft` IS NULL
          AND      `parents`.`lft`  IS NOT NULL
        LIMIT      1;

        # Finding the element's parent.
        SELECT  `parent_id`
          INTO  currentParentId
        FROM    `tmp_tree`
        WHERE   `id` = currentId;

        # Finding the parent's lft value.
        SELECT  `lft`
          INTO  currentLeft
        FROM    `tmp_tree`
        WHERE   `id` = currentParentId;

        # Shifting all elements to the right of the current element 2 to the right.
        UPDATE `tmp_tree`
        SET    `rght` = `rght` + 2
        WHERE  `rght` > currentLeft;

        UPDATE `tmp_tree`
        SET    `lft` = `lft` + 2
        WHERE  `lft` > currentLeft;

        # Setting lft and rght values for current element.
        UPDATE `tmp_tree`
        SET    `lft`  = currentLeft + 1,
               `rght` = currentLeft + 2
        WHERE  `id`   = currentId;

    END WHILE;

    # Writing calculated values back to physical table.
    UPDATE `tree`, `tmp_tree`
    SET    `tree`.`lft`  = `tmp_tree`.`lft`,
           `tree`.`rght` = `tmp_tree`.`rght`
    WHERE  `tree`.`id`   = `tmp_tree`.`id`;

    COMMIT;

    DROP TABLE `tmp_tree`;

END//

DELIMITER ;

S některými testovacími daty to fungovalo dobře, ale stále běží na mém stromu 100 000 záznamů, takže zatím nemohu vydat žádný konečný soud. Naivní skript pracující přímo na fyzickém stole má propastný výkon, běží minimálně hodiny, spíše dny. Přepnutím na dočasnou tabulku MEMORY se tato doba zkrátila asi na hodinu a výběrem správných indexů se zkrátila na 10 minut.