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Description

The `BITFIELDOVERFLOW` error in Redis occurs when a `BITFIELD` operation attempts to set a value that exceeds the maximum or falls below the minimum representable value for the specified data type and offset. This results in an integer overflow error during bit manipulation.

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Error Message

ERR BITFIELD overflow value is not an integer or out of range

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Known Causes

3 known causes

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Value Out of Range

The provided value for the `BITFIELD` operation is larger than the maximum allowable value or smaller than the minimum allowable value for the specified data type.

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Incorrect Offset

The specified offset, combined with the data type's bit width, results in an attempt to write beyond the boundaries of the allocated bitfield.

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Data Type Mismatch

The value provided is of an unexpected data type (e.g., string instead of integer) or does not align with the expected bit width of the field.

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Solutions

4 solutions available

1. Verify Data Type and Bit Size easy

Ensure the data type (e.g., i8, u8, i16, u16, i32, u32, i64, u64) and the number of bits specified in your BITFIELD command are appropriate for the intended range of values.

1

Identify the BITFIELD command that is causing the overflow. Examine the arguments, particularly the data type and the offset/bit specification.

Example of a problematic BITFIELD command:
BITFIELD mykey SET u8 0 260

2

Understand the range of values for the chosen data type. For example, `u8` (unsigned 8-bit integer) can hold values from 0 to 255. `i8` (signed 8-bit integer) can hold values from -128 to 127. If you attempt to set a value like 260 to a `u8`, it will overflow.

Common integer ranges:
- u8: 0 to 255
- i8: -128 to 127
- u16: 0 to 65535
- i16: -32768 to 32767
- u32: 0 to 4294967295
- i32: -2147483648 to 2147483647
- u64: 0 to 18446744073709551615
- i64: -9223372036854775808 to 9223372036854775807

3

Adjust the data type or the value being set to fit within the valid range. If you need to store larger values, consider using a wider data type (e.g., `u16`, `u32`, `u64`).

Corrected BITFIELD command:
BITFIELD mykey SET u8 0 250  # Value 250 fits within u8
BITFIELD mykey SET u16 0 300 # If 300 is needed, use u16

2. Adjusting the Offset for Larger Values medium

If you are using a fixed-size data type but need to store a value that would overflow at the current offset, you can use subsequent bits by increasing the offset. This effectively uses more bits to represent a larger number.

1

Analyze the BITFIELD command and the value being set. Determine if the value requires more bits than the current data type and offset allow.

Problematic command:
BITFIELD mykey SET u8 5 200  # Assuming this causes overflow at offset 5 with u8

2

Understand how offsets work. Each bit in a Redis string is addressable. An offset of `N` means the `N`-th bit from the start of the string. When using `BITFIELD` with a specific data type, the command reserves `data_type_bits` for that value starting at the specified offset.

Example: `SET u8 5 200` reserves 8 bits starting from bit 5. This means bits 5, 6, 7, 8, 9, 10, 11, 12 are used for this value.

3

If the value exceeds the capacity at the current offset, consider using a larger offset to allocate more bits for the value. This might involve using a larger data type implicitly or explicitly if the offset requires it.

If you need to store a value that requires more than 8 bits (e.g., 300), and `u8` is insufficient even with a larger offset, you'd need to use a larger data type like `u16` or `u32`.

However, if the overflow is due to the *combination* of offset and data type, and you can conceptually break down the value or use subsequent bits, adjust the offset. For instance, if you were storing a value that could be represented by two `u8`s concatenated:

BITFIELD mykey SET u8 0 100 SET u8 8 200 # Uses 8 bits for 100, then another 8 bits for 200.

4

If the goal is to store a single, larger integer, and the overflow persists with `u64`, you might need to reconsider your data modeling or use multiple Redis keys to store parts of the larger number.

Consider using `u64` if your values are within its range:
BITFIELD mykey SET u64 0 1234567890123456789

3. Handling Signed vs. Unsigned Integers easy

The `BITFIELD` command supports both signed and unsigned integer types. Ensure you are using the correct type (signed `i*` or unsigned `u*`) based on whether your values can be negative. Using an unsigned type for negative values will lead to incorrect interpretation and potential overflows.

1

Review the `BITFIELD` command and the nature of the data you are storing. Determine if negative values are possible.

Example scenario: Storing deltas or differences which can be positive or negative.

2

If your values can be negative, use a signed integer type (e.g., `i8`, `i16`, `i32`, `i64`). If your values are always non-negative, use an unsigned integer type (e.g., `u8`, `u16`, `u32`, `u64`).

Incorrect usage (storing negative value in unsigned type):
BITFIELD mykey SET u8 0 -50  # This will likely cause an overflow or unexpected behavior

Correct usage (storing negative value in signed type):
BITFIELD mykey SET i8 0 -50

3

Be mindful of the range differences between signed and unsigned types of the same bit width. For example, `i8` ranges from -128 to 127, while `u8` ranges from 0 to 255. A value like 200 stored in an `i8` would overflow.

If you need to store values between 128 and 255, you must use an unsigned type like `u8`.
If you need to store values between -128 and -1, you must use a signed type like `i8`.

4. Re-evaluating Data Modeling and Redis Capabilities advanced

If the `BITFIELDOVERFLOW` error persists after checking data types, offsets, and signed/unsigned usage, it might indicate that the intended data or scale of operations is exceeding the practical limits of a single Redis bitfield. Consider alternative data structures or splitting the data.

1

Assess the maximum possible value you need to store and the total number of bits required. Calculate the total size of the bitfield needed.

Example: If you need to store a value that requires 100 bits, and you are using `u64` (64 bits), you will inevitably overflow if you try to set it in one go without careful management.

2

If the required number of bits exceeds `u64` (64 bits) and you cannot fit your data into a single 64-bit integer, consider using multiple Redis keys to represent a larger arbitrary-precision integer. For instance, you could use two `u64` fields to represent a 128-bit integer.

Representing a 128-bit integer with two keys:
BITFIELD key_high SET u64 0 <high_bits>
BITFIELD key_low SET u64 0 <low_bits>

3

Alternatively, if your data is a collection of related values, consider using other Redis data structures like Hashes or Sorted Sets. Hashes can store multiple key-value pairs within a single Redis key, and Sorted Sets are ideal for ordered collections.

Using a Hash to store multiple related values:
HMSET myhash field1 100 field2 250

4

For very large integers that go beyond the practical limits of multiple `u64` fields, you might need to implement custom logic in your application to manage arbitrary-precision arithmetic and store the result in a string or serialized format, rather than relying solely on Redis `BITFIELD` for the entire representation.

Example (conceptual, requires application logic):
Store a large number as a base-2 string and parse/manipulate it in your application.

Fix Redis BITFIELDOVERFLOW: Integer Overflow