Column definitions not cached for calculations on has_many association with :include

It appears the problem also occurs with a simple call to .joins() in combination with has_many associations:

Article.joins(:comments).first # Retrieves column definitions from db every single time.

I have updated the patch with a second failing test for this case.

Hi Emilio,

Thank you for your answer. I was using the PostgreSQL adapter in my original application. If you try it in a real application, you'll see in the Rails log that all queries are being executed in succession, no caching is applied in the cases I mentioned.

I'm looking at the source of ActiveRecord::ConnectionAdapters::PostgreSQLAdapter#columns, and I can't find any caching strategy being used. The #columns method calls #column_definitions directly, which calls the #query method, which executes a db query on the underlying pg library.

I'm also pretty sure that assert_queries does not count the queries that are executed directly from the database adapter this way. In the test helper of ActiveRecord I can see that the connection's #execute method is overridden, but not #query.

For MySQL however, the call to MySQLAdapter#columns does use #execute internally. But note that in the definition of execute_with_query_record (in activerecord/test/cases/helper.rb, which overrides the #execute method to store all executed queries for testing purposes), a check is made to see if the query should be ignored! The definition of IGNORED_SQL there specifically includes /SHOW FIELDS/.

Finally, for SQLite3, the call to SQLite3Adapter#columns calls #table_structure directly on the sqlite library, which also has no caching strategy and which also does not pass through the filter of assert_queries (it bypasses #execute on the connection adapter).

Please, let me know how I can adjust the test cases to make them clearer. The call to #columns is the only place in the connection adapter interface I could find that is shared between all adapters. In all three cases I tried (MySQL, PostgreSQL and SQLite3) I have been able to verify that there is 1) no caching strategy in the adapter and 2) the query is not caught by assert_queries. Should assert_queries be adjusted? Does the connection adapter even need to implement the caching, or should it be done in a higher abstraction level? I'm definitely willing to assist in solving this problem, but currently I can't seem to pinpoint exactly where the column definition caching is done right now (or should be done).

Also, note that calling .count on an association without :include does properly use cached column definitions. The first of the tests below succeeds, the second fails. What is the difference in implementation?

def test_calculations_on_has_many_association_should_not_reload_column_definitions
  Author.last.posts.count
  Author.connection.expects(:columns).never
  Author.last.posts.count
end

def test_calculations_on_has_many_association_with_include_should_not_reload_column_definitions
  Author.last.posts_with_comments.count
  Author.connection.expects(:columns).never
  Author.last.posts_with_comments.count
end

Rolf,

I tried running this test on MySQL, PostgreSQL and Sqlite3:

  def test_calculations_on_has_many_association_with_include_should_not_reload_column_definitions
    logger = ActiveRecord::Base.logger
    logger.warn("STARTS first count")
    assert_queries 2 do
      Author.last.posts_with_comments.count
    end
    logger.warn("ENDS first count")
    logger.warn("STARTS second count")
    assert_queries 2 do
      Author.last.posts_with_comments.count
    end
    logger.warn("ENDS second count")
  end

On PostgreSQL. The test passed, and the output on debug.log was:

STARTS first count
  Author Load (0.6ms)  SELECT "authors".* FROM "authors" ORDER BY authors.id DESC LIMIT 1
  SQL (0.8ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (1.1ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.8ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.7ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.7ms)  SELECT COUNT(DISTINCT "posts"."id") AS count_id FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id" WHERE ("posts".author_id = 2)
ENDS first count
STARTS second count
  Author Load (0.3ms)  SELECT "authors".* FROM "authors" ORDER BY authors.id DESC LIMIT 1
  SQL (0.7ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.4ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.6ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.4ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.3ms)  SELECT COUNT(DISTINCT "posts"."id") AS count_id FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id" WHERE ("posts".author_id = 2)
ENDS second count

On SQLite3, the test also passed and the output was simpler:

STARTS first count
  Author Load (0.3ms)  SELECT "authors".* FROM "authors" ORDER BY authors.id DESC LIMIT 1
  SQL (0.2ms)  SELECT COUNT(DISTINCT "posts"."id") AS count_id FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id" WHERE ("posts".author_id = 2)
ENDS first count
STARTS second count
  Author Load (0.1ms)  SELECT "authors".* FROM "authors" ORDER BY authors.id DESC LIMIT 1
  SQL (0.2ms)  SELECT COUNT(DISTINCT "posts"."id") AS count_id FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id" WHERE ("posts".author_id = 2)
ENDS second count

On MySQL the test passed with debug.log output:

STARTS first count
  Author Load (0.8ms)  SELECT `authors`.* FROM `authors` ORDER BY authors.id DESC LIMIT 1
  SQL (1.1ms)  SELECT COUNT(DISTINCT `posts`.`id`) AS count_id FROM `posts` LEFT OUTER JOIN `comments` ON `comments`.`post_id` = `posts`.`id` WHERE (`posts`.author_id = 2)
ENDS first count
STARTS second count
  Author Load (0.2ms)  SELECT `authors`.* FROM `authors` ORDER BY authors.id DESC LIMIT 1
  SQL (0.6ms)  SELECT COUNT(DISTINCT `posts`.`id`) AS count_id FROM `posts` LEFT OUTER JOIN `comments` ON `comments`.`post_id` = `posts`.`id` WHERE (`posts`.author_id = 2)
ENDS second count
  SQL (0.2ms)  ROLLBACK

I tried defining IGNORED_SQL as an empty array, SQLite3 and postgreSQL tests were green but MySQL failed with the following test output:

9 instead of 2 queries were executed.
Queries:
SELECT     `authors`.* FROM       `authors`  ORDER BY  authors.id DESC LIMIT 1
SHOW FIELDS FROM `comments`
SHOW FIELDS FROM `posts`
SHOW FIELDS FROM `posts`
SHOW FIELDS FROM `comments`
SHOW FIELDS FROM `comments`
SHOW FIELDS FROM `posts`
SHOW FIELDS FROM `comments`
SELECT     COUNT(DISTINCT `posts`.`id`) AS count_id FROM       `posts`  LEFT OUTER JOIN `comments` ON `comments`.`post_id` = `posts`.`id` WHERE     (`posts`.author_id = 2).
<2> expected but was
<9>.

I think a problem may be in PostgreSQL, i added a debug line in PostgreSQLAdapter#columns, ran the same test and had the following output:

STARTS first count
  Author Load (16.3ms)  SELECT "authors".* FROM "authors" ORDER BY authors.id DESC LIMIT 1
Columns for comments with name comments Columns
  SQL (0.7ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for posts with name posts Columns
  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for posts with name posts Columns
  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for comments with name comments Columns
  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for comments with name comments Columns
  SQL (0.7ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for posts with name posts Columns
  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for comments with name comments Columns
  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.8ms)  SELECT COUNT(DISTINCT "posts"."id") AS count_id FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id" WHERE ("posts".author_id = 2)
ENDS first count
STARTS second count
  Author Load (0.3ms)  SELECT "authors".* FROM "authors" ORDER BY authors.id DESC LIMIT 1
Columns for comments with name comments Columns
  SQL (0.7ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for posts with name posts Columns
  SQL (0.6ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for comments with name comments Columns
  SQL (0.6ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for comments with name comments Columns
  SQL (0.6ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for posts with name posts Columns
  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"posts"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

Columns for comments with name comments Columns
  SQL (0.5ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"comments"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum

  SQL (0.4ms)  SELECT COUNT(DISTINCT "posts"."id") AS count_id FROM "posts" LEFT OUTER JOIN "comments" ON "comments"."post_id" = "posts"."id" WHERE ("posts".author_id = 2)
ENDS second count

If you try the same on other adapters you will get something like this:

  SQL (0.1ms)  BEGIN
STARTS first count
  Author Load (0.3ms)  SELECT `authors`.* FROM `authors` ORDER BY authors.id DESC LIMIT 1
Columns for comments with name comments Columns
Columns for posts with name posts Columns
Columns for posts with name posts Columns
Columns for comments with name comments Columns
Columns for comments with name comments Columns
Columns for posts with name posts Columns
Columns for comments with name comments Columns
  SQL (0.4ms)  SELECT COUNT(DISTINCT `posts`.`id`) AS count_id FROM `posts` LEFT OUTER JOIN `comments` ON `comments`.`post_id` = `posts`.`id` WHERE (`posts`.author_id = 2)
ENDS first count
STARTS second count
  Author Load (0.2ms)  SELECT `authors`.* FROM `authors` ORDER BY authors.id DESC LIMIT 1
Columns for comments with name comments Columns
Columns for posts with name posts Columns
Columns for comments with name comments Columns
Columns for comments with name comments Columns
Columns for posts with name posts Columns
Columns for comments with name comments Columns
  SQL (0.3ms)  SELECT COUNT(DISTINCT `posts`.`id`) AS count_id FROM `posts` LEFT OUTER JOIN `comments` ON `comments`.`post_id` = `posts`.`id` WHERE (`posts`.author_id = 2)
ENDS second count
  SQL (0.1ms)  ROLLBACK

Hi Emilio,

Your results seem consistent with mine insofar I've tried them (will do more tests later). What struck me the first time as well, is that in all cases where column definition caching fails on PostgreSQL, the number of calls to the #columns method on the connection adapter is less on the second call, no matter the adapter. From the output of your final log the columns for comments are loaded 4 times and 3 times for posts, vs. 4x comments and 2x posts (!) after the second query.

It seems like there is an intention to cache the column definitions before they hit the connection adapter. Do you agree that the second time that an ActiveRecord relation is retrieved, ideally there should be no calls at all to #columns on the connection adapter? If so, I will read some more Rails 3 source code to start working on a patch.

I have been experiencing this issue as well since I upgraded 3.0.0.beta3 to 3.0.0.beta4

Why is this marked as spam? Several people have confirmed that they are experiencing this issue?

I am still seeing this issue in 3.0.0.rc.

Any news on this so far? I'm having the same problem with postgresql.
Besides the performance implications, the extra queries really bloat the debug log.

I'm seeing the same issue. In fact, it doesn't seem to have anything to do with :has_many or joins...if a table is queried, the query is immediately followed by this "SELECT a.attname ..." query.

example:

Started GET "/" for 127.0.0.1 at 2010-08-07 01:17:06 -0500
  Processing by ItemsController#index as HTML
  Item Load (0.4ms)  SELECT "items".* FROM "items"
  SQL (0.7ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"items"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum







  Image Load (2.4ms)  SELECT "images".* FROM "images" WHERE (item_id IN (2,3)) ORDER BY "order" ASC
  SQL (0.8ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"images"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum







Rendered orders/item_quantity.html.erb (0.6ms)
  SQL (0.8ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"users"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum
  User Load (0.5ms)  SELECT "users".* FROM "users" WHERE ("users"."id" = 2) LIMIT 1
  SQL (0.6ms)   SELECT a.attname, format_type(a.atttypid, a.atttypmod), d.adsrc, a.attnotnull
 FROM pg_attribute a LEFT JOIN pg_attrdef d
 ON a.attrelid = d.adrelid AND a.attnum = d.adnum
 WHERE a.attrelid = '"users"'::regclass
 AND a.attnum > 0 AND NOT a.attisdropped
 ORDER BY a.attnum
Rendered items/show.html.erb (157.4ms)
Rendered orders/item_quantity.html.erb (0.5ms)
  CACHE (0.0ms)  SELECT "users".* FROM "users" WHERE ("users"."id" = 2) LIMIT 1
Rendered items/show.html.erb (6.7ms)
  CACHE (0.0ms)  SELECT "users". FROM "users" WHERE ("users"."id" = 2) LIMIT 1
  CACHE (0.0ms)  SELECT "users". FROM "users" WHERE ("users"."id" = 2) LIMIT 1
  CACHE (0.0ms)  SELECT "users". FROM "users" WHERE ("users"."id" = 2) LIMIT 1
  CACHE (0.0ms)  SELECT "users". FROM "users" WHERE ("users"."id" = 2) LIMIT 1
Rendered items/index.html.erb within layouts/application (170.5ms)
Completed 200 OK in 233ms (Views: 171.8ms | ActiveRecord: 6.2ms)

I was digging through the commits from 3.0.0.beta3 to 3.0.0.beta4 to try and track down the issue. I didn't see anything that looked like it was causing it, but obviously I missed something.

The biggest change I noticed was a move to the pg gem. Not sure if that has anything to do with it though.

Automatic cleanup of spam.

This is not spam. It is still a bug in 3.0.0.

I'm not sure if it hasn't been already fixed in #5392 column_definitions method being called before and after every single SQL stat...

Automatic cleanup of spam.

I tested for this behaviour recently with Rails edge. It seems to be solved by the fix to #5392 column_definitions method being called before and after every single SQL stat....

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