Avoid N+1 query in large data set
I have a migration which updates existing records with a new attribute value. The model is called 'MyRecord'. It has millions of records in the database with a new unit_id column of null. I want to update that unit_id column with a specific value:
MyRecord.find_each do |record|
unit_id = Unit.calculate_unit_from_old_columns(record.legacy_column_1, record.legacy_column_2).first.id
record.update unit_id: unit_id
end
This creates a lot of N+1 queries:
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
UPDATE my_records SET unit_id='43' WHERE legacy_column_1 = 'Legacy Electronics' AND legacy_column_2 = 'Legacy Auto';
And some of these N+1 queries are duplicated. I see a lot of this in logs:
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
I am familiar with eager loading via includes. But when this migration is run to update existing data, there will be no association yet. So I cannot do this:
record.includes(:unit)
How can I eliminate the N+1 queries and cache the query so it does not hit database again when s duplicate query?
mysql sql ruby-on-rails
asked Nov 14 '18 at 22:27
DonatoDonato
2,07431434
|
show 3 more comments
I have a migration which updates existing records with a new attribute value. The model is called 'MyRecord'. It has millions of records in the database with a new unit_id column of null. I want to update that unit_id column with a specific value:
MyRecord.find_each do |record|
unit_id = Unit.calculate_unit_from_old_columns(record.legacy_column_1, record.legacy_column_2).first.id
record.update unit_id: unit_id
end
This creates a lot of N+1 queries:
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
UPDATE my_records SET unit_id='43' WHERE legacy_column_1 = 'Legacy Electronics' AND legacy_column_2 = 'Legacy Auto';
And some of these N+1 queries are duplicated. I see a lot of this in logs:
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
I am familiar with eager loading via includes. But when this migration is run to update existing data, there will be no association yet. So I cannot do this:
record.includes(:unit)
How can I eliminate the N+1 queries and cache the query so it does not hit database again when s duplicate query?
mysql sql ruby-on-rails
asked Nov 14 '18 at 22:27
DonatoDonato
2,07431434
How complicated iscalculate_unit_from_old_columns? It'd be best to move everything to the updating query (SET unit_id = DO_STUFF(legacy_column_1, legacy_column_2). If it's too complicated, you should prepare batch updates (map 1000 records to(id, new_unit_id)pairs and use those for update queries.
– Marcin Kołodziej
Nov 14 '18 at 22:34
@MarcinKołodziej can you give me an example of batch updates or point me to a link?
– Donato
Nov 14 '18 at 22:37
calculate_unit_from_old_columns is a named scope: scope : calculate_unit_from_old_columns, ->(item1, item2) { where(item_1: item1, item2: item_2 ) }
– Donato
Nov 14 '18 at 22:38
Oh, right, it's quite a long line. Well, you can write a simple update with join. You tagged your question with MySQL and PostgreSQL and they have different syntax for that, it should be easily searchable.
– Marcin Kołodziej
Nov 14 '18 at 22:44
@MarcinKołodziej I am using MySQL
– Donato
Nov 14 '18 at 22:45
|
show 3 more comments
I have a migration which updates existing records with a new attribute value. The model is called 'MyRecord'. It has millions of records in the database with a new unit_id column of null. I want to update that unit_id column with a specific value:
MyRecord.find_each do |record|
unit_id = Unit.calculate_unit_from_old_columns(record.legacy_column_1, record.legacy_column_2).first.id
record.update unit_id: unit_id
end
This creates a lot of N+1 queries:
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
UPDATE my_records SET unit_id='43' WHERE legacy_column_1 = 'Legacy Electronics' AND legacy_column_2 = 'Legacy Auto';
And some of these N+1 queries are duplicated. I see a lot of this in logs:
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
I am familiar with eager loading via includes. But when this migration is run to update existing data, there will be no association yet. So I cannot do this:
record.includes(:unit)
How can I eliminate the N+1 queries and cache the query so it does not hit database again when s duplicate query?
mysql sql ruby-on-rails
asked Nov 14 '18 at 22:27
DonatoDonato
2,07431434
I have a migration which updates existing records with a new attribute value. The model is called 'MyRecord'. It has millions of records in the database with a new unit_id column of null. I want to update that unit_id column with a specific value:
MyRecord.find_each do |record|
unit_id = Unit.calculate_unit_from_old_columns(record.legacy_column_1, record.legacy_column_2).first.id
record.update unit_id: unit_id
end
This creates a lot of N+1 queries:
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
UPDATE my_records SET unit_id='43' WHERE legacy_column_1 = 'Legacy Electronics' AND legacy_column_2 = 'Legacy Auto';
And some of these N+1 queries are duplicated. I see a lot of this in logs:
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
SELECT units.* FROM units WHERE units.item_1 = 'Electronics' AND units.item_2 = 'Auto'
I am familiar with eager loading via includes. But when this migration is run to update existing data, there will be no association yet. So I cannot do this:
record.includes(:unit)
How can I eliminate the N+1 queries and cache the query so it does not hit database again when s duplicate query?
mysql sql ruby-on-rails
mysql sql ruby-on-rails
asked Nov 14 '18 at 22:27
DonatoDonato
2,07431434
asked Nov 14 '18 at 22:27
DonatoDonato
2,07431434
edited Nov 14 '18 at 22:45
Donato
asked Nov 14 '18 at 22:27
DonatoDonato
2,07431434
asked Nov 14 '18 at 22:27
DonatoDonato
2,07431434
asked Nov 14 '18 at 22:27
DonatoDonato
2,07431434
2,07431434
How complicated iscalculate_unit_from_old_columns? It'd be best to move everything to the updating query (SET unit_id = DO_STUFF(legacy_column_1, legacy_column_2). If it's too complicated, you should prepare batch updates (map 1000 records to(id, new_unit_id)pairs and use those for update queries.
– Marcin Kołodziej
Nov 14 '18 at 22:34
@MarcinKołodziej can you give me an example of batch updates or point me to a link?
– Donato
Nov 14 '18 at 22:37
calculate_unit_from_old_columns is a named scope: scope : calculate_unit_from_old_columns, ->(item1, item2) { where(item_1: item1, item2: item_2 ) }
– Donato
Nov 14 '18 at 22:38
Oh, right, it's quite a long line. Well, you can write a simple update with join. You tagged your question with MySQL and PostgreSQL and they have different syntax for that, it should be easily searchable.
– Marcin Kołodziej
Nov 14 '18 at 22:44
@MarcinKołodziej I am using MySQL
– Donato
Nov 14 '18 at 22:45
|
show 3 more comments
How complicated iscalculate_unit_from_old_columns? It'd be best to move everything to the updating query (SET unit_id = DO_STUFF(legacy_column_1, legacy_column_2). If it's too complicated, you should prepare batch updates (map 1000 records to(id, new_unit_id)pairs and use those for update queries.
– Marcin Kołodziej
Nov 14 '18 at 22:34
@MarcinKołodziej can you give me an example of batch updates or point me to a link?
– Donato
Nov 14 '18 at 22:37
calculate_unit_from_old_columns is a named scope: scope : calculate_unit_from_old_columns, ->(item1, item2) { where(item_1: item1, item2: item_2 ) }
– Donato
Nov 14 '18 at 22:38
Oh, right, it's quite a long line. Well, you can write a simple update with join. You tagged your question with MySQL and PostgreSQL and they have different syntax for that, it should be easily searchable.
– Marcin Kołodziej
Nov 14 '18 at 22:44
@MarcinKołodziej I am using MySQL
– Donato
Nov 14 '18 at 22:45
How complicated is
calculate_unit_from_old_columns? It'd be best to move everything to the updating query (SET unit_id = DO_STUFF(legacy_column_1, legacy_column_2). If it's too complicated, you should prepare batch updates (map 1000 records to (id, new_unit_id) pairs and use those for update queries.– Marcin Kołodziej
Nov 14 '18 at 22:34
How complicated is
calculate_unit_from_old_columns? It'd be best to move everything to the updating query (SET unit_id = DO_STUFF(legacy_column_1, legacy_column_2). If it's too complicated, you should prepare batch updates (map 1000 records to (id, new_unit_id) pairs and use those for update queries.– Marcin Kołodziej
Nov 14 '18 at 22:34
@MarcinKołodziej can you give me an example of batch updates or point me to a link?
– Donato
Nov 14 '18 at 22:37
@MarcinKołodziej can you give me an example of batch updates or point me to a link?
– Donato
Nov 14 '18 at 22:37
calculate_unit_from_old_columns is a named scope: scope : calculate_unit_from_old_columns, ->(item1, item2) { where(item_1: item1, item2: item_2 ) }
– Donato
Nov 14 '18 at 22:38
calculate_unit_from_old_columns is a named scope: scope : calculate_unit_from_old_columns, ->(item1, item2) { where(item_1: item1, item2: item_2 ) }
– Donato
Nov 14 '18 at 22:38
Oh, right, it's quite a long line. Well, you can write a simple update with join. You tagged your question with MySQL and PostgreSQL and they have different syntax for that, it should be easily searchable.
– Marcin Kołodziej
Nov 14 '18 at 22:44
Oh, right, it's quite a long line. Well, you can write a simple update with join. You tagged your question with MySQL and PostgreSQL and they have different syntax for that, it should be easily searchable.
– Marcin Kołodziej
Nov 14 '18 at 22:44
@MarcinKołodziej I am using MySQL
– Donato
Nov 14 '18 at 22:45
@MarcinKołodziej I am using MySQL
– Donato
Nov 14 '18 at 22:45
|
show 3 more comments
1 Answer
1
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votes
Use a simple query, you can think of batching it if it runs for too long:
MyRecord.connection.execute(
"UPDATE my_records, units
SET unit_id = units.id
WHERE units.item_1 = legacy_column_1 AND units.item_2 = legacy_column_2"
)
answered Nov 14 '18 at 22:54
Marcin KołodziejMarcin Kołodziej
4,4801315
add a comment |
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1 Answer
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1 Answer
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active
oldest
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Use a simple query, you can think of batching it if it runs for too long:
MyRecord.connection.execute(
"UPDATE my_records, units
SET unit_id = units.id
WHERE units.item_1 = legacy_column_1 AND units.item_2 = legacy_column_2"
)
answered Nov 14 '18 at 22:54
Marcin KołodziejMarcin Kołodziej
4,4801315
add a comment |
Use a simple query, you can think of batching it if it runs for too long:
MyRecord.connection.execute(
"UPDATE my_records, units
SET unit_id = units.id
WHERE units.item_1 = legacy_column_1 AND units.item_2 = legacy_column_2"
)
answered Nov 14 '18 at 22:54
Marcin KołodziejMarcin Kołodziej
4,4801315
add a comment |
Use a simple query, you can think of batching it if it runs for too long:
MyRecord.connection.execute(
"UPDATE my_records, units
SET unit_id = units.id
WHERE units.item_1 = legacy_column_1 AND units.item_2 = legacy_column_2"
)
answered Nov 14 '18 at 22:54
Marcin KołodziejMarcin Kołodziej
4,4801315
Use a simple query, you can think of batching it if it runs for too long:
MyRecord.connection.execute(
"UPDATE my_records, units
SET unit_id = units.id
WHERE units.item_1 = legacy_column_1 AND units.item_2 = legacy_column_2"
)
answered Nov 14 '18 at 22:54
Marcin KołodziejMarcin Kołodziej
4,4801315
answered Nov 14 '18 at 22:54
Marcin KołodziejMarcin Kołodziej
4,4801315
answered Nov 14 '18 at 22:54
Marcin KołodziejMarcin Kołodziej
4,4801315
answered Nov 14 '18 at 22:54
Marcin KołodziejMarcin Kołodziej
4,4801315
4,4801315
add a comment |
add a comment |
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How complicated is
calculate_unit_from_old_columns? It'd be best to move everything to the updating query (SET unit_id = DO_STUFF(legacy_column_1, legacy_column_2). If it's too complicated, you should prepare batch updates (map 1000 records to(id, new_unit_id)pairs and use those for update queries.– Marcin Kołodziej
Nov 14 '18 at 22:34
@MarcinKołodziej can you give me an example of batch updates or point me to a link?
– Donato
Nov 14 '18 at 22:37
calculate_unit_from_old_columns is a named scope: scope : calculate_unit_from_old_columns, ->(item1, item2) { where(item_1: item1, item2: item_2 ) }
– Donato
Nov 14 '18 at 22:38
Oh, right, it's quite a long line. Well, you can write a simple update with join. You tagged your question with MySQL and PostgreSQL and they have different syntax for that, it should be easily searchable.
– Marcin Kołodziej
Nov 14 '18 at 22:44
@MarcinKołodziej I am using MySQL
– Donato
Nov 14 '18 at 22:45