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perf(results): build typed columns directly from the driver stream instead of collecting List<List<Object?>> first

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
42/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
dart, mysql, postgresql, sqlite
Domain
database, performance

Research direction

Read postgres_sql_workspace.dart, mysql_sql_workspace.dart, and sqlite_sql_workspace.dart to trace how each driver currently collects rows and builds CompactResultDataset; then inspect CompactResultDataset.fromRawRows and the related work in #1548. Define a shared builder that preserves current mixed-type and NULL behavior, and use existing dataset tests to check it across all three drivers. Done means those tests pass and the PR reports peak RSS and timings for 5k and 50k rows.

Written by the indexing model from the issue text.

Description

backend core enhancement P3 performance
Problem

Each SQL driver workspace builds an intermediate List<List<Object?>> of the whole result and only then packs it into typed columns (CompactResultDataset.fromRawRows):

  • PostgreSQL (postgres_sql_workspace.dart): rawRows.add(row.toList()) for every row.
  • MySQL (mysql_sql_workspace.dart): taken.items (all ResultSetRows kept) and then [for (i...) row.colAt(i)] per row.
  • SQLite: same pattern (sqlite_sql_workspace.dart).

So every cell is copied into a per-row list once, kept alive until the dataset is built, and then read again column by column.

Measurements

Local PostgreSQL 16 / MySQL 8.4 containers, 100k rows x 20 columns, dart run, median of 3:

Driver Rows Network + decode Extra row copy Longest event-loop stall during it
PostgreSQL 5,000 21-22 ms 1-3 ms (row.toList) 0 ms
PostgreSQL 50,000 257-271 ms 10-19 ms 0-2 ms
MySQL 5,000 31-38 ms 2-5 ms (colAt) 4-7 ms
MySQL 50,000 296-320 ms 33-42 ms 7-15 ms

(The decode itself yields between socket chunks: the PostgreSQL driver blocks the event loop for 0-2 ms even at 50k rows, so moving the driver into a worker isolate would not remove a visible hitch; it only adds connect cost and a result hand-off. Not recommended.)

Solution

Let the driver loop append into column builders (int / double / string / generic with a null bitmap) as rows arrive, deciding the kind from the first rows and falling back to generic when a value does not fit, instead of collecting List<List<Object?>>. A small ResultColumnsBuilder would be shared by the three drivers and by #1548's sampled detection.

Expected: removes the 1-3 ms (5k) / 10-40 ms (50k) copy and the peak memory of the intermediate list, and makes the "decode / pack" step incremental.

Acceptance
  • A shared builder used by PostgreSQL, MySQL and SQLite workspaces; existing dataset tests unchanged.
  • Mixed-type and NULL-heavy columns still end up as generic / string exactly as today (tests).
  • Peak RSS and time for 5k and 50k rows reported in the PR.

Related: #1548, #1549.

Dominant language
Dart
Stars
23
Forks
1
Avg merge
45m
Merged PRs (30d)
529

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