microsoft/garnet · error · TsavoriteException

Segment ({SegmentSize}) must be at least of page size ({Page

Error message

Segment ({SegmentSize}) must be at least of page size ({PageSize})

What it means

Thrown in the segment-size step: SegmentSize (1 << SegmentSizeBits) must be >= PageSize (1 << PageSizeBits), because segments are groups of pages and cannot be smaller than a single page. Even when each of PageSizeBits and SegmentSizeBits is individually in range (errors 222 and 225), a large page combined with a smaller segment trips this; e.g. PageSizeBits=25 (32MiB) with SegmentSizeBits=12 (4KiB) => 4KiB < 32MiB.

Source

Thrown at libs/storage/Tsavorite/cs/src/core/Allocator/AllocatorBase.cs:639

                MaxAllocatedPageCount = logSettings.PageCount > 0 ? logSettings.PageCount : (int)(logSettings.MemorySize / PageSize);
            }
            else
            {
                if (logSettings.PageCount <= 0)
                    throw new TsavoriteException($"Log Memory size or PageCount must be specified");
                MaxAllocatedPageCount = logSettings.PageCount;
            }
            BufferSize = (int)NextPowerOf2(MaxAllocatedPageCount);

            BufferSizeMask = BufferSize - 1;

            logMutableFraction = logSettings.MutableFraction;

            // Segment size
            LogSegmentSizeBits = logSettings.SegmentSizeBits;
            SegmentSize = 1L << LogSegmentSizeBits;
            if (SegmentSize < PageSize)
                throw new TsavoriteException($"Segment ({SegmentSize}) must be at least of page size ({PageSize})");

            PageStatusIndicator = new FullPageStatus[BufferSize];

            if (!IsNullDevice)
            {
                PendingFlush = new PendingFlushList[BufferSize];
                for (int i = 0; i < BufferSize; i++)
                    PendingFlush[i] = new PendingFlushList();
            }
            device = logSettings.LogDevice;
            sectorSize = (int)device.SectorSize;

            if (PageSize < sectorSize)
                throw new TsavoriteException($"Page size must be at least of device sector size ({sectorSize} bytes). Set PageSizeBits accordingly.");

            AlignedPageSizeBytes = RoundUp(PageSize, sectorSize);

            if (BufferSize > 0)

View on GitHub (pinned to 951b0fc683)

Solutions

  1. Ensure SegmentSizeBits >= PageSizeBits (so each segment holds at least one page).
  2. When raising PageSizeBits, raise SegmentSizeBits to match or exceed it.
  3. Keep the defaults (PageSizeBits=25, SegmentSizeBits=30) unless you have measured reason to change both consistently.

Example fix

// before
logSettings.PageSizeBits   = 25;  // 32MiB page
logSettings.SegmentSizeBits = 12;  // 4KiB segment -> < page
// after
logSettings.SegmentSizeBits = 30;  // 1GiB segment >= 32MiB page
Defensive patterns

Strategy: validation

Validate before calling

// Segment must be >= page: SegmentSizeBits >= PageSizeBits.
if (logSettings.SegmentSizeBits < logSettings.PageSizeBits)
    logSettings.SegmentSizeBits = logSettings.PageSizeBits;  // or larger, e.g. +5

Try / catch

try { new TsavoriteKV<K,V>(logSettings, ...); }
catch (TsavoriteException ex) when (ex.Message.Contains("Segment") && ex.Message.Contains("at least of page size"))
{ /* raise SegmentSizeBits to >= PageSizeBits and recreate */ }

Prevention

When it happens

Trigger: Setting SegmentSizeBits < PageSizeBits, or raising PageSizeBits above the existing SegmentSizeBits without also raising the segment size.

Common situations: Tuning PageSizeBits up for fewer, larger flush units and forgetting to bump SegmentSizeBits; mirroring a config where the two were changed independently.

Related errors

AI-assisted analysis of microsoft/garnet@951b0fc683 (2026-08-13). Data as JSON: /api/errors/55db727e7e1a1ac3. Report an issue: GitHub.