1# Perfetto UI 2 3[Perfetto UI](https://ui.perfetto.dev) enables you to view and analyze traces in 4the browser. It supports several different tracing formats, including the 5perfetto proto trace format and the legacy json trace format. 6 7## UI Tips and Tricks 8 9### Debug Slices 10 11Sometimes you may want to insert some fake slices into the timeline to help 12with your understanding of the data. You can do so by inserting rows into a 13magic `debug_slices` table. 14 15`debug_slices` table has five columns: 16 17* `id` (integer) [optional] If present, Perfetto UI will use it as slice id to 18 open the details panel when you click on the slices. 19* `name` (string) [optional] The displayed slice title. 20* `ts` (integer) [required] Start of the slice, in nanoseconds. 21* `dur` (integer) [required] Duration of the slice, in nanoseconds. Determines 22 slice width. 23* `depth` (integer) [optional] The row at which the slice is drawn. Depth 0 is 24 the first row. 25 26You can open the debug track by going to the "Sample queries" menu on the 27left, and clicking "Show Debug Track". A debug slice track will become pinned to 28the top and will initially be empty. After you insert slices in the 29`debug_slices` table, you can click the reload button on the track to refresh 30the information shown in that track. 31 32Here is a simple example with random slices to illustrate the use: 33 34```sql 35CREATE VIEW rand_slices AS SELECT * FROM SLICE 36 ORDER BY RANDOM() LIMIT 2000; 37 38INSERT INTO debug_slices(id, name, ts, dur, depth) 39 SELECT id, name, ts, dur, depth FROM RAND_SLICES; 40``` 41 42After you click the reload button, you should see the slices in the debug track. 43 44 45 46Once you're done, you can click the X button to hide the track, and you can 47clear the `debug_slices` table (`DELETE FROM debug_slices`) to clear the track. 48 49A more interesting example is seeing RAIL modes in chrome traces: 50 51```sql 52SELECT RUN_METRIC('chrome/rail_modes.sql'); 53 54-- Depth 0 is the unified RAIL Mode 55INSERT INTO debug_slices 56 SELECT NULL, rail_mode, ts, dur, 0 FROM combined_overall_rail_slices; 57 58-- Depth 2+ are for each Renderer process with depth 1 left blank 59INSERT INTO debug_slices 60 SELECT NULL, short_name, ts, dur, depth + 1 FROM rail_mode_slices, 61 (SELECT track_id, row_number() OVER () AS depth FROM 62 (SELECT DISTINCT track_id FROM rail_mode_slices)) depth_map, 63 rail_modes 64 WHERE depth_map.track_id = rail_mode_slices.track_id 65 AND rail_mode=rail_modes.mode; 66``` 67 68This produces a visualization like this: 69 70 71 72Note: There is no equivalent debug counters feature yet, but the feature request 73is tracked on [b/168886909](http://b/168886909)). 74 75### Pivot Tables 76 77To use pivot tables in the Perfetto UI, you will need to enable the 78"Pivot tables" feature flag in the "Flags" tab under "Support" in the Sidebar. 79You can pop up a pivot table over the entire trace when clicking "p" on your 80keyboard. The "Edit" button opens a pop up window to add/remove and reorder 81columns and change the default sorting of aggregations. 82 83 84 85Clicking on "Query" generates a table with the selected columns. 86Table cells with the expand icon can be expanded to show the next column values. 87The "name (stack)" column displays top level slices that can be expanded to show 88their descendants down to the last child. 89 90 91 92Area selection pops up a pre-filled pivot table restricted over the selected 93timestamps and track ids. 94 95 96
