> ## Documentation Index > Fetch the complete documentation index at: https://docs.optimism.io/llms.txt > Use this file to discover all available pages before exploring further. # Batches A [Batch][batch] contains a list of transactions to be included in a specific L2 block. Since the [Delta hardfork][delta], there are two Batch types or variants: [`SingleBatch`][single-batch] and [`SpanBatch`][span-batch]. ## Where Batches fit in the OP Stack The [Batch][batch] is the highest-level data type in the OP Stack derivation process that comes prior to building payload attributes. A [Batch][batch] is constructed by taking the raw data from a [Channel][channel], decompressing it, and decoding the [Batch][batch] from this decompressed data. Alternatively, when looking at the [Batch][batch] type from a batching perspective, and not from the derivation perspective, the [Batch][batch] type contains a list of L2 transactions and is compressed into the [`Channel`][channel] type. In turn, the [`Channel`][channel] is split into frames which are posted to the data availability layer through batcher transactions. ## Contents of a `Batch` A [`Batch`][batch] is either a [`SingleBatch`][single-batch] or a [`SpanBatch`][span-batch], each with their own contents. Below, these types are broken down in their respective sections. ### `SingleBatch` Type The [`SingleBatch`][single-batch] type contains the following. * A [`BlockHash`][block-hash] parent hash that represents the parent L2 block. * A `u64` epoch number that identifies the [epoch][epoch] for this batch. * A [`BlockHash`][block-hash] epoch hash. * The timestamp for the batch as a `u64`. * A list of EIP-2718 encoded transactions (represented as [`Bytes`][bytes]). In order to validate the [`SingleBatch`][single-batch] once decoded, the [`SingleBatch::check_batch`][check-batch-single] method should be used, providing the rollup config, l1 blocks, l2 safe head, and inclusion block. ### `SpanBatch` Type The [`SpanBatch`][span-batch] type (available since the [Delta hardfork][delta]) comprises the data needed to build a "span" of multiple L2 blocks. It contains the following data. * The parent check (the first 20 bytes of the block's parent hash). * The l1 origin check (the first 20 bytes of the last block's l1 origin hash). * The genesis timestamp. * The chain id. * A list of [`SpanBatchElement`][span-batch-element]s. These are similar to the [`SingleBatch`][single-batch] type but don't contain the parent hash and epoch hash for this L2 block. * Origin bits. * Block transaction counts. * Span batch transactions which contain information for transactions in a span batch. Similar to the `SingleBatch` type discussed above, the [`SpanBatch`][span-batch] type must be validated once decoded. For this, the [`SpanBatch::check_batch`][check-batch-span] method is available. After the [Holocene hardfork][holocene] was introduced, span batch validation is greatly simplified to be forwards-invalidating instead of backwards-invalidating, so a new [`SpanBatch::check_batch_prefix`][check-batch-prefix] method provides a way to validate each batch as it is loaded, in an iterative fashion. ## Batch Encoding The first byte of the decompressed channel data is the [`BatchType`][batch-type], which identifies whether the batch is a [`SingleBatch`][single-batch] or a [`SpanBatch`][span-batch]. From there, the respective type is decoded, and [derived][derived] in the case of the [`SpanBatch`][span-batch]. The `Batch` encoding format for the [`SingleBatch`][single-batch] is broken down [in the specs][specs]. ## The `Batch` Type The [`Batch`][batch] type itself only provides two useful methods. * [`timestamp`][timestamp] returns the timestamp of the [`Batch`][batch] * [`decode`][decode], constructs a new [`Batch`][batch] from the provided raw, decompressed batch data and rollup config. Within each [`Batch`][batch] variant, the individual types contain more functionality. [holocene]: https://specs.optimism.io/protocol/holocene/overview.html [check-batch-prefix]: https://docs.rs/kona-protocol/latest/kona_protocol/struct.SpanBatch.html#method.check_batch_prefix [check-batch-span]: https://docs.rs/kona-protocol/latest/kona_protocol/struct.SpanBatch.html#method.check_batch [span-batch-element]: https://docs.rs/kona-protocol/latest/kona_protocol/struct.SpanBatchElement.html [check-batch-single]: https://docs.rs/kona-protocol/latest/kona_protocol/struct.SingleBatch.html#method.check_batch [bytes]: https://docs.rs/alloy-primitives/latest/alloy_primitives/struct.Bytes.html [block-hash]: https://docs.rs/alloy-primitives/latest/alloy_primitives/aliases/type.BlockHash.html [epoch]: https://specs.optimism.io/glossary.html?highlight=Epoch#sequencing-epoch [decode]: https://docs.rs/kona-protocol/latest/kona_protocol/enum.Batch.html#method.decode [timestamp]: https://docs.rs/kona-protocol/latest/kona_protocol/enum.Batch.html#method.timestamp [specs]: https://specs.optimism.io/protocol/derivation.html#batch-format [derived]: https://docs.rs/kona-protocol/latest/kona_protocol/struct.RawSpanBatch.html#method.derive [batch-type]: https://docs.rs/kona-protocol/latest/kona_protocol/enum.BatchType.html [channel]: https://docs.rs/kona-protocol/latest/kona_protocol/struct.Channel.html [batch]: https://docs.rs/kona-protocol/latest/kona_protocol/enum.Batch.html [span-batch]: https://docs.rs/kona-protocol/latest/kona_protocol/struct.SpanBatch.html [single-batch]: https://docs.rs/kona-protocol/latest/kona_protocol/struct.SingleBatch.html [delta]: https://specs.optimism.io/protocol/delta/overview.html