Commit 6e51bf4b authored by Mayra Cabrera's avatar Mayra Cabrera

Merge branch '30453-add-migration-helpers-for-limiting-text-columns' into 'master'

Add migration helpers for managing check constraints and limits on text columns

See merge request gitlab-org/gitlab!29181
parents 4ea94c9a be5469f9
...@@ -1178,8 +1178,147 @@ into similar problems in the future (e.g. when new tables are created). ...@@ -1178,8 +1178,147 @@ into similar problems in the future (e.g. when new tables are created).
end end
end end
# Returns the name for a check constraint
#
# type:
# - Any value, as long as it is unique
# - Constraint names are unique per table in Postgres, and, additionally,
# we can have multiple check constraints over a column
# So we use the (table, column, type) triplet as a unique name
# - e.g. we use 'max_length' when adding checks for text limits
# or 'not_null' when adding a NOT NULL constraint
#
def check_constraint_name(table, column, type)
identifier = "#{table}_#{column}_check_#{type}"
# Check concurrent_foreign_key_name() for info on why we use a hash
hashed_identifier = Digest::SHA256.hexdigest(identifier).first(10)
"check_#{hashed_identifier}"
end
def check_constraint_exists?(table, constraint_name)
# Constraint names are unique per table in Postgres, not per schema
# Two tables can have constraints with the same name, so we filter by
# the table name in addition to using the constraint_name
check_sql = <<~SQL
SELECT COUNT(*)
FROM pg_constraint
JOIN pg_class ON pg_constraint.conrelid = pg_class.oid
WHERE pg_constraint.contype = 'c'
AND pg_constraint.conname = '#{constraint_name}'
AND pg_class.relname = '#{table}'
SQL
connection.select_value(check_sql).positive?
end
# Adds a check constraint to a table
#
# This method is the generic helper for adding any check constraint
# More specialized helpers may use it (e.g. add_text_limit or add_not_null)
#
# This method only requires minimal locking:
# - The constraint is added using NOT VALID
# This allows us to add the check constraint without validating it
# - The check will be enforced for new data (inserts) coming in
# - If `validate: true` the constraint is also validated
# Otherwise, validate_check_constraint() can be used at a later stage
# - Check comments on add_concurrent_foreign_key for more info
#
# table - The table the constraint will be added to
# check - The check clause to add
# e.g. 'char_length(name) <= 5' or 'store IS NOT NULL'
# constraint_name - The name of the check constraint (otherwise auto-generated)
# Should be unique per table (not per column)
# validate - Whether to validate the constraint in this call
#
# rubocop:disable Gitlab/RailsLogger
def add_check_constraint(table, check, constraint_name, validate: true)
# Transactions would result in ALTER TABLE locks being held for the
# duration of the transaction, defeating the purpose of this method.
if transaction_open?
raise 'add_check_constraint can not be run inside a transaction'
end
if check_constraint_exists?(table, constraint_name)
warning_message = <<~MESSAGE
Check constraint was not created because it exists already
(this may be due to an aborted migration or similar)
table: #{table}, check: #{check}, constraint name: #{constraint_name}
MESSAGE
Rails.logger.warn warning_message
else
# Only add the constraint without validating it
# Even though it is fast, ADD CONSTRAINT requires an EXCLUSIVE lock
# Use with_lock_retries to make sure that this operation
# will not timeout on tables accessed by many processes
with_lock_retries do
execute <<-EOF.strip_heredoc
ALTER TABLE #{table}
ADD CONSTRAINT #{constraint_name}
CHECK ( #{check} )
NOT VALID;
EOF
end
end
if validate
validate_check_constraint(table, constraint_name)
end
end
def validate_check_constraint(table, constraint_name)
unless check_constraint_exists?(table, constraint_name)
raise missing_schema_object_message(table, "check constraint", constraint_name)
end
disable_statement_timeout do
# VALIDATE CONSTRAINT only requires a SHARE UPDATE EXCLUSIVE LOCK
# It only conflicts with other validations and creating indexes
execute("ALTER TABLE #{table} VALIDATE CONSTRAINT #{constraint_name};")
end
end
def remove_check_constraint(table, constraint_name)
# DROP CONSTRAINT requires an EXCLUSIVE lock
# Use with_lock_retries to make sure that this will not timeout
with_lock_retries do
execute <<-EOF.strip_heredoc
ALTER TABLE #{table}
DROP CONSTRAINT IF EXISTS #{constraint_name}
EOF
end
end
# Migration Helpers for adding limit to text columns
def add_text_limit(table, column, limit, constraint_name: nil, validate: true)
add_check_constraint(
table,
"char_length(#{column}) <= #{limit}",
text_limit_name(table, column, name: constraint_name),
validate: validate
)
end
def validate_text_limit(table, column, constraint_name: nil)
validate_check_constraint(table, text_limit_name(table, column, name: constraint_name))
end
def remove_text_limit(table, column, constraint_name: nil)
remove_check_constraint(table, text_limit_name(table, column, name: constraint_name))
end
def check_text_limit_exists?(table, column, constraint_name: nil)
check_constraint_exists?(table, text_limit_name(table, column, name: constraint_name))
end
private private
def text_limit_name(table, column, name: nil)
name.presence || check_constraint_name(table, column, 'max_length')
end
def missing_schema_object_message(table, type, name) def missing_schema_object_message(table, type, name)
<<~MESSAGE <<~MESSAGE
Could not find #{type} "#{name}" on table "#{table}" which was referenced during the migration. Could not find #{type} "#{name}" on table "#{table}" which was referenced during the migration.
......
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