Insert into a new collection on an existing DB file fails: 'Not enough space' on an unreadable/stale page

[IAFahim]

Summary

Opening an existing .db file with a DbContext that declares a new collection (one not present when the file was created) makes the first insert into that collection throw:

System.InvalidOperationException: Not enough space: need 54, have 0
  | PageId=67 | SlotCount=0 | Start=0 | End=0 | FSI=16306

This blocks a normal schema-evolution scenario: ship app v1 with collection A, then v2 adds collection B — existing user files crash on first write to B.

Minimal repro (BLite 5.1.1, net10.0)

using BLite.Bson;
using BLite.Core;
using BLite.Core.Collections;
using ReproApp;

const string Path = "repro.db";

// Pass 1: create db + collection A, insert, close.
if (!File.Exists(Path))
{
    using (var db = new ADbContext(Path))
    {
        await db.A.InsertAsync(new A { Name = "one" });
        await db.SaveChangesAsync();
    }
    Console.WriteLine("pass 1: created collection A");
}

// Pass 2: reopen same file, insert into NEW collection B -> throws.
using (var db = new BDbContext(Path))
{
    await db.B.InsertAsync(new B { Name = "two" });
    await db.SaveChangesAsync();
    Console.WriteLine("pass 2: collection B OK");
}

namespace ReproApp
{
    public class A { public ObjectId Id { get; set; } public string Name { get; set; } = ""; }
    public class B { public ObjectId Id { get; set; } public string Name { get; set; } = ""; }

    public partial class ADbContext : DocumentDbContext
    {
        public DocumentCollection<ObjectId, A> A { get; set; } = null!;
        public ADbContext(string path) : base(path) => InitializeCollections();
    }
    public partial class BDbContext : DocumentDbContext
    {
        public DocumentCollection<ObjectId, B> B { get; set; } = null!;
        public BDbContext(string path) : base(path) => InitializeCollections();
    }
}

Output:

pass 1: created collection A
Unhandled exception. System.InvalidOperationException: Not enough space: need 54, have 0 | PageId=67 | SlotCount=0 | Start=0 | End=0 | FSI=16306
   at BLite.Core.Collections.DocumentCollection`2.InsertIntoPage(...)

Hypothesis (unverified)

In FreeSpaceIndexProvider, a single FreeSpaceIndex is shared across all collections when UsesSeparateCollectionFiles == false. For the new collection the FSI believes page 67 has ~16 KB free (fresh-page size), but the page's on-disk header reads SlotCount=0, FreeSpaceStart=0, FreeSpaceEnd=0 with a non-Empty PageType, so the zeroed-page recovery branch in InsertIntoPage (PageType == Empty && FreeSpaceEnd == 0) doesn't trigger. Possibly an allocated-but-never-initialized (or recycled) page getting a full-size FSI entry.

Environment

• BLite 5.1.1 (net10.0 target), .NET 10.0.4xx SDK, Linux x64
• Reproduces 100% with the steps above on a fresh file

Generated with Devin

[mrdevrobot]

Triage: confirmed on 5.1.1 (main @ 019ab02).

Reproduced exactly as in the report (create file with context A, reopen with a context declaring new collection B, first insert):

System.InvalidOperationException: Not enough space: need 54, have 0 | PageId=67 | SlotCount=0 | Start=0 | End=0 | FSI=16306

The hypothesis in the report (FSI entry for a never-initialised page, so the zeroed-page recovery in InsertIntoPage does not trigger) is still to be verified, but the symptom matches. Likely related to #151 (pages allocated outside committed state).

Status: confirmed, fix in progress. High priority (breaks schema evolution on existing files).

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Generated by Claude Code

[mrdevrobot]

@IAFahim this is fixed by #155 and released in BLite 5.2.1 (now on NuGet). Pages freed when orphan collections are dropped are now invalidated in the shared free-space index, so the first insert into a collection added to an existing file no longer lands on a stale page. Two rarer edge cases around the free-space index are known and not covered yet: rolling back an open transaction can restore stale values, and invalidated pages can linger in the index. Thanks for the report. @mrdevrobot

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Generated by Claude Code