Reader: optimize ReaderPostTable.comparePosts

[nbradbury]

Background

ReaderPostTable.comparePosts() is the gate that ReaderPostLocalSource.saveUpdatedPosts uses to decide what to do after the Reader fetches posts from the server. Its three-valued result drives three distinct behaviors in the caller:

• HAS_NEW / CHANGED — runs the full write path: gap detection, delete-and-reinsert for REQUEST_REFRESH, addOrUpdatePosts, bookmark pseudo-id fixups, gap-marker placement, and the UI change events those trigger.
• UNCHANGED — skips the write path entirely, avoiding re-inserting rows we already have and suppressing UI refreshes when nothing has actually changed.
• UNCHANGED + REQUEST_OLDER_THAN_GAP — a special case where a gap-fill request returned nothing new, signalling that the gap marker was bogus and should be removed.

In short, comparePosts answers "does the server response differ from what's already stored?" — used to short-circuit writes and UI refreshes on no-op refreshes, and to distinguish "gap filled nothing" from a real update.

Description

ReaderPostTable.comparePosts() previously ran one getBlogPost() SQL query per incoming post, each materializing a full ReaderPost that was thrown away after the isSamePost check. For a typical Reader refresh of ~20 posts that's 20 round-trips to SQLite.

This change replaces those N queries with a single SELECT keyed by (blog_id, post_id) via OR clauses, loads the matching rows into an in-memory map (using the existing COLUMN_NAMES_NO_TEXT projection and getPostFromCursor), and has the comparison loop probe the map.

Fix to isSamePost text comparison

While optimizing this, we noticed comparePosts was also effectively never returning UNCHANGED for full-text streams. It loads existing rows with excludeTextColumn=true, but ReaderPost.isSamePost unconditionally compared post.getText().equals(existingPost.getText()). Since the stored side was always empty, any incoming post with a non-empty body was reported as CHANGED — forcing saveUpdatedPosts down the full write path on every refresh.

To fix this, isSamePost now has an overload with a compareText flag so UNCHANGED now fires correctly - and more often - on true no-op refreshes and the caller can skip re-inserting rows and firing UI change events.

Testing instructions

Reader refresh smoke test:

1. Open the Reader and pull to refresh a followed tag / site stream.

• Verify posts load and any new/changed posts are reflected in the list.

2. Scroll to trigger paging / background refresh of the same stream.

• Verify no duplicate or missing posts appear compared to prior behavior.

[dangermattic]

	1 Warning
⚠️	PR is not assigned to a milestone.

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Android by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Android
	Build Type	Debug
	Version	pr22810-b6bdf43
	Build Number	1488
	Application ID	com.jetpack.android.prealpha
	Commit	b6bdf43
	Installation URL	05p7jaddn753g

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[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Android by scanning the QR code below to install the corresponding build.

	App Name	WordPress Android
	Build Type	Debug
	Version	pr22810-b6bdf43
	Build Number	1488
	Application ID	org.wordpress.android.prealpha
	Commit	b6bdf43
	Installation URL	6ivcgpmbken38

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.15%. Comparing base (79d417d) to head (b6bdf43).

Files with missing lines	Patch %	Lines
...rg/wordpress/android/datasets/ReaderPostTable.java	0.00%	17 Missing ⚠️
.../java/org/wordpress/android/models/ReaderPost.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk   #22810      +/-   ##
==========================================
- Coverage   37.15%   37.15%   -0.01%     
==========================================
  Files        2314     2314              
  Lines      124294   124310      +16     
  Branches    16882    16884       +2     
==========================================
  Hits        46185    46185              
- Misses      74366    74382      +16     
  Partials     3743     3743              

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