Re: slow subquery

[Matthias Horn]

Hello Igor, hello Michael,

the actual query is:
Delete from "UserFields" where not exists (select "idThumb" from "Thumbnail" where "idThumb" = "idThumbUDF")

It is intended to delete orphaned records with user fields and runs on each move of a thumb.
The databases officially supported for ThumbsPlus (esp. Jet Engine and MS SQL) seem to handle such queries very well.

I'm running MySQL 5.0.17 on a (a bit outdated) Intel Debian machine. Together with ThumbsPlus it does an impressing good job and gives very short response times for all actions besides the ones involving the query mentioned above.

The tables are defined as follows:
CREATE TABLE "UserFields" (
"idThumbUDF" INT(11) NOT NULL,
# about 130 columns of the type
"uf_XYZ" LONGTEXT,
....
PRIMARY KEY ("idThumbUDF")
) TYPE=InnoDB;

CREATE TABLE "Thumbnail" (
"idThumb" INT(11) NOT NULL AUTO_INCREMENT,
"idPath" INT(11) NOT NULL ,
"idFiletype" INT(11) DEFAULT NULL,
"file_time" INT(11) DEFAULT NULL,
"thumbnail_time" INT(11) DEFAULT NULL,
"filesize" INT(11) DEFAULT NULL,
"checksum" INT(11) DEFAULT NULL,
"width" INT(11) DEFAULT NULL,
"height" INT(11) DEFAULT NULL,
"horiz_res" INT(11) DEFAULT NULL,
"vert_res" INT(11) DEFAULT NULL,
"colortype" SMALLINT(6) DEFAULT NULL,
"colordepth" SMALLINT(6) DEFAULT NULL,
"gamma" SMALLINT(6) DEFAULT NULL,
"thumbnail_width" SMALLINT(6) NOT NULL,
"thumbnail_height" SMALLINT(6) NOT NULL,
"thumbnail_type" INT(11) DEFAULT NULL,
"thumbnail_size" INT(11) DEFAULT NULL,
"name" VARCHAR(255) DEFAULT NULL,
"Thumbnail" LONGBLOB,
"annotation" TEXT,
"metric1" TINYBLOB,
"metric2" TINYBLOB,
"metric3" TINYBLOB,
PRIMARY KEY ("idThumb"),
INDEX ("idPath"),
INDEX ("name"),
INDEX ("idPath","name")
) TYPE=InnoDB;

In my database both tables contain about 14000 rows.
The query takes about 100 seconds and does not delete any row.

Since the people here are not able to change the query, a solution which requires only some reconfiguring of the database (configuration, engine, indexes, triggers) itself would be very helpful.

Regards,
Matthias