microsoft/FASTER · error · FasterException

BlittableAllocator memory pages are sector aligned - use…

Error message

BlittableAllocator memory pages are sector aligned - use direct copy

What it means

PopulatePage copies caller-supplied bytes into a freshly allocated page; blittable pages are already sector-aligned device memory filled directly by I/O, so software population is meaningless and intentionally unimplemented. The override throws FasterException to catch any code path attempting the object-allocator's page-population flow on a BlittableAllocator.

Solutions

Do not call PopulatePage for blittable logs; pages are filled directly via device I/O with sector-aligned copies.
If copying into a blittable page, write to the page's pointer (direct memcpy) respecting sector alignment instead of the PopulatePage hook.
If object-style population is needed, switch to the ObjectAllocator (class-typed Key/Value).

Example fix

// before
allocator.PopulatePage(src, requiredBytes, destinationPage); // on BlittableAllocator

// after
// copy directly into the aligned page buffer:
Buffer.MemoryCopy((void*)pagePointer, (void*)src, requiredBytes, requiredBytes);

Defensive patterns

Strategy: validation

Validate before calling

// internal API: only call PopulatePage on ObjectAllocator, never BlittableAllocator
if (allocator is BlittableAllocator<K, V>)
    throw new InvalidOperationException("Use direct sector-aligned copy for blittable pages");

Type guard

bool NeedsPopulatePage(FasterKV<K, V>.ILogAllocator a) => a is ObjectAllocator<K, V>;

Try / catch

try { allocator.PopulatePage(src, bytes, page); }
catch (FasterException ex) when (ex.Message.Contains("sector aligned - use direct copy")) { /* memcpy into page pointer instead */ }

Prevention

Model custom device/commit code on the allocator type you actually use.
For blittable logs, always copy via the page pointer with sector alignment.
Gate internal population paths on allocator type checks.

When it happens

Trigger: An internal or custom code path invoking PopulatePage on the BlittableAllocator - e.g. a custom allocator/commit-manager patch, or object-log-style page fill logic reused against a blittable log.

Common situations: Extending FASTER with custom device/commit logic modeled on the object allocator; misuse of internal (internal-visibility) APIs in patched builds rather than end-user scenarios.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of microsoft/FASTER@321d872eab (2026-09-15). Data as JSON: /api/errors/389d6ec5c0f27810. Report an issue: GitHub.

Appendix: source

Thrown at cs/src/core/Allocator/BlittableAllocator.cs:372

        /// Whether KVS has values to serialize/deserialize
        /// </summary>
        /// <returns></returns>
        public override bool ValueHasObjects()
        {
            return false;
        }

        public override IHeapContainer<Key> GetKeyContainer(ref Key key) => new StandardHeapContainer<Key>(ref key);
        public override IHeapContainer<Value> GetValueContainer(ref Value value) => new StandardHeapContainer<Value>(ref value);

        public override long[] GetSegmentOffsets()
        {
            return null;
        }

        internal override void PopulatePage(byte* src, int required_bytes, long destinationPage)
        {
            throw new FasterException("BlittableAllocator memory pages are sector aligned - use direct copy");
        }

        /// <summary>
        /// Iterator interface for pull-scanning FASTER log
        /// </summary>
        public override IFasterScanIterator<Key, Value> Scan(FasterKV<Key, Value> store, long beginAddress, long endAddress, ScanBufferingMode scanBufferingMode) 
            => new BlittableScanIterator<Key, Value>(store, this, beginAddress, endAddress, scanBufferingMode, epoch, logger: logger);

        /// <summary>
        /// Implementation for push-scanning FASTER log, called from LogAccessor
        /// </summary>
        internal override bool Scan<TScanFunctions>(FasterKV<Key, Value> store, long beginAddress, long endAddress, ref TScanFunctions scanFunctions, ScanBufferingMode scanBufferingMode)
        {
            using BlittableScanIterator<Key, Value> iter = new(store, this, beginAddress, endAddress, scanBufferingMode, epoch, logger: logger);
            return PushScanImpl(store, beginAddress, endAddress, ref scanFunctions, iter);
        }

        /// <summary>

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