Report reindexing metrics in log

lib/gitlab/database/postgres_index.rb

@@ -32,6 +32,8 @@ module Gitlab
         where('NOT EXISTS (?)', recent_actions)
       end
 
+      alias_method :reset, :reload
+
       def bloat_size
         strong_memoize(:bloat_size) { bloat_estimate&.bloat_size || 0 }
       end

lib/gitlab/database/reindexing/reindex_concurrently.rb

@@ -3,6 +3,7 @@
 module Gitlab
   module Database
     module Reindexing
+      # This is a >= PG12 reindexing strategy based on `REINDEX CONCURRENTLY`
       class ReindexConcurrently
         include Gitlab::Utils::StrongMemoize
 
@@ -39,17 +40,47 @@ module Gitlab
           # While this has been backpatched, we continue to disable expression indexes until further review.
           raise ReindexError, 'expression indexes are currently not supported' if index.expression?
 
-          logger.info "Starting reindex of #{index}"
-
-          set_statement_timeout do
-            execute("REINDEX INDEX CONCURRENTLY #{quote_table_name(index.schema)}.#{quote_table_name(index.name)}")
+          with_logging do
+            set_statement_timeout do
+              execute("REINDEX INDEX CONCURRENTLY #{quote_table_name(index.schema)}.#{quote_table_name(index.name)}")
+            end
           end
+
         ensure
           cleanup_dangling_indexes
         end
 
         private
 
+        def with_logging
+          bloat_size = index.bloat_size
+          ondisk_size_before = index.ondisk_size_bytes
+
+          logger.info(
+            message: "Starting reindex of #{index}",
+            index: index.identifier,
+            table: index.tablename,
+            estimated_bloat_bytes: bloat_size,
+            index_size_before_bytes: ondisk_size_before
+          )
+
+          duration = Benchmark.realtime do
+            yield
+          end
+
+          index.reset
+
+          logger.info(
+            message: "Finished reindex of #{index}",
+            index: index.identifier,
+            table: index.tablename,
+            estimated_bloat_bytes: bloat_size,
+            index_size_before_bytes: ondisk_size_before,
+            index_size_after_bytes: index.ondisk_size_bytes,
+            duration_s: duration.round(2)
+          )
+        end
+
         def cleanup_dangling_indexes
           Gitlab::Database::PostgresIndex.match("#{Regexp.escape(index.name)}#{TEMPORARY_INDEX_PATTERN}").each do |lingering_index|
             remove_index(lingering_index)

spec/lib/gitlab/database/reindexing/reindex_concurrently_spec.rb

@@ -8,7 +8,7 @@ RSpec.describe Gitlab::Database::Reindexing::ReindexConcurrently, '#perform' do
   let(:table_name) { '_test_reindex_table' }
   let(:column_name) { '_test_column' }
   let(:index_name) { '_test_reindex_index' }
-  let(:index) { instance_double(Gitlab::Database::PostgresIndex, indexrelid: 42, name: index_name, schema: 'public', tablename: table_name, partitioned?: false, unique?: false, exclusion?: false, expression?: false, definition: 'CREATE INDEX _test_reindex_index ON public._test_reindex_table USING btree (_test_column)') }
+  let(:index) { Gitlab::Database::PostgresIndex.by_identifier("public.#{index_name}") }
   let(:logger) { double('logger', debug: nil, info: nil, error: nil ) }
   let(:connection) { ActiveRecord::Base.connection }
 
@@ -18,7 +18,7 @@ RSpec.describe Gitlab::Database::Reindexing::ReindexConcurrently, '#perform' do
         id serial NOT NULL PRIMARY KEY,
         #{column_name} integer NOT NULL);
 
-      CREATE INDEX #{index.name} ON #{table_name} (#{column_name});
+      CREATE INDEX #{index_name} ON #{table_name} (#{column_name});
     SQL
   end