rusackas opened a new pull request, #40238:
URL: https://github.com/apache/superset/pull/40238

   ### SUMMARY
   
   Addresses a kapa.ai coverage gap on dashboard chart loading and performance. 
Users repeatedly hit the support bot with three questions that have no clear 
answer in the docs today:
   
   > - is there a maximum chart count per dashboard?
   > - is there a flag to cap concurrent chart loads on a dashboard?
   > - is there an option to lazy-load tabs rather than preloading everything?
   
   Existing docs mention `DASHBOARD_VIRTUALIZATION` only in the feature-flags 
listing, with no behavioral detail. The bot has been guessing from GitHub 
issues and recommending source-reading.
   
   This PR adds a single focused page at 
`/admin-docs/configuration/dashboard-performance` that answers each question 
authoritatively, drawing the behavioral specifics directly from the code:
   
   - **Max chart count**: no hard cap in code or config. Practical thresholds 
(~25 fine, 25–50 needs tabs, 50+ split or use tabs aggressively) with caveats.
   - **`DASHBOARD_VIRTUALIZATION`** (default `True`, stable, 
path-to-deprecation): row-level viewport rendering — chart mounts when within 1 
viewport-height of view, unmounts when >4 viewport-heights away. Pulled from 
`superset-frontend/src/dashboard/components/gridComponents/Row/Row.tsx`. Noted 
exceptions for embedded mode (no unmount) and headless/bot rendering (no 
virtualization, so reports include every chart).
   - **`DASHBOARD_VIRTUALIZATION_DEFER_DATA`** (default `False`): supplementary 
flag, defers the data fetch on top of the render gating.
   - **Per-tab lazy loading**: on by default, no flag — tabs render content 
only when activated.
   - **Concurrent-query cap**: none in Superset. Browser caps ~6 in-flight per 
origin; backend bounded by Gunicorn / Celery worker count.
   - **Splitting strategies** in escalating effort: tabs → cache → async 
queries → multiple dashboards → warehouse-side pre-aggregation. Cross-links to 
Caching, Async Queries, Feature Flags docs.
   
   ### BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF
   
   N/A — new docs page.
   
   ### TESTING INSTRUCTIONS
   
   ```bash
   cd docs && yarn install && yarn build
   ```
   
   Build passes locally with `onBrokenLinks: throw`. New page appears in the 
sidebar at `/admin-docs/configuration/dashboard-performance` (position 5, 
grouped with cache + async-queries since they're all perf-related).
   
   ### ADDITIONAL INFORMATION
   - [ ] Has associated issue:
   - [ ] Required feature flags:
   - [ ] Changes UI
   - [ ] Includes DB Migration (follow approval process in 
[SIP-59](https://github.com/apache/superset/issues/13351))
     - [ ] Migration is atomic, supports rollback & is backwards-compatible
     - [ ] Confirm DB migration upgrade and downgrade tested
     - [ ] Runtime estimates and downtime expectations provided
   - [ ] Introduces new feature or API
   - [ ] Removes existing feature or API
   


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