docs(clp-s): Add skeleton for clp-s design documentation; Write first half of clp-s single-file archive design document.

docs/src/dev-guide/design-clp-structured/background.md

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+# Background
+
+The [KV-IR background section](../design-kv-ir-streams/background.md) contains partial background
+information about clp-s.
+
+:::{warning}
+🚧 This section is still under construction.
+:::

docs/src/dev-guide/design-clp-structured/index.md

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+# clp-s
+
+The compressed-log-processor-structured (abbreviated `clp-s`, also known as [μSlope][μSlope])
+archive format is a storage format for large chunks of dynamically-structured (e.g., JSON) logs.
+Compared to the [KV-IR](../design-kv-ir-streams/index.md) streaming compression format, `clp-s`
+achieves higher compression ratios and significantly faster search speeds. To accomplish this, `clp-s` needs to
+aggregate log data before compressing the data into archives. In addition, it requires memory proportional to
+archive size for both compression and search. These constraints make `clp-s` unsuitable for real-time or severely
+resource-constrained usage, but ideal for long-term archival and search.
+
+::::{grid} 1 1 1 1
+:gutter: 2
+
+:::{grid-item-card}
+:link: background
+Background
+^^^
+All information needed to understand `clp-s`' format.
+:::
+
+:::{grid-item-card}
+:link: single-file-archive-format
+Single-file archive format
+^^^
+A detailed reference for the single-file archive format.
+:::
+::::
+
+:::{warning}
+🚧 This section is still under construction.
+:::
+
+:::{toctree}
+:hidden:
+
+background
+single-file-archive-format
+:::
+
+[μSlope]: https://www.usenix.org/conference/osdi24/presentation/wang-rui

docs/src/dev-guide/design-clp-structured/single-file-archive-format.md

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+# Single-file archive format
+
+The `clp-s` single-file archive format is designed to offer high compression and fast search on
+dynamically-structured log data such as JSON logs. This format is optimized for streaming reads in
+order to enable high performance for archives stored on object storage systems such as
+[S3][amazon-s3].
+
+This documentation records the details of the single-file archive (v0.3.1) format and what it
+enables, with minimal discussion of design rationale. For more information about the design
+decisions behind `clp-s`, please refer to [our paper on `clp-s`][μSlope], or our [blog][s3-blog] on
+optimizing `clp-s` for object storage.
+
+## Format overview
+
+The single-file archive format is divided into the `header`, `metadata`, and `files` sections, as
+shown in [Figure 1](#figure-1). All archives begin with a 64-byte header that contains important
+metadata, such as the archive format version and information needed to read the
+`metadata` section. The `metadata` section is made up of several independent "metadata packets" that
+contain archive-level metadata such as the range of timestamp values present in an archive and
+information needed to read the `files` section. The `files` section contains the data structures 
+used to represent log data and makes up most of the size of an archive; the `files` section is named
+as such because its various components exist as individual files in the multi-file archive format.
+
+:::{note}
+The single-file archive format is little-endian. Therefore, all fields in the remainder of this
+document should be treated as little-endian unless specified otherwise. Furthermore, any
+"struct-like" descriptions of binary formats should be interpreted as _not_ having padding for
+alignment, e.g. an `int32_t` followed by an `int64_t` should be interpreted as a 12-byte structure
+without padding.
+:::
+
+(figure-1)=
+::::{card}
+:::{mermaid}
+%%{
+  init: {
+    "theme": "base",
+    "themeVariables": {
+      "primaryColor": "#0066cc",
+      "primaryTextColor": "#fff",
+      "primaryBorderColor": "transparent",
+      "lineColor": "#007fff",
+      "secondaryColor": "#007fff",
+      "tertiaryColor": "#fff"
+    }
+  }
+}%%
+block-beta
+  columns 1
+  header
+  metadata
+  block:files_group:1
+    columns 1
+    files
+    block:files_detail
+        mpt["/schema_tree"] sm["/schema_ids"] tm["/table_metadata"] vd["/var.dict"] ld["/log.dict"]
+        ad["/array.dict"] t["/0"]
+    end
+  end
+:::
++++
+**Figure 1**: High-level single-file archive layout.
+::::
+
+## Header section
+
+The archive header is a 64-byte unit at the start of a single-file archive that contains some of the
+most important metadata information about an archive, as shown in [Figure 2](#figure-2). The header
+begins with a 4-byte magic number which identifies the file as an archive. The magic number is
+followed by a 4-byte version number, comprised of a 2-byte patch version number, followed by 1-byte
+minor and major version numbers respectively. For version 0.X.Y archives, every minor version
+change is breaking. To reduce maintenance while the archive format stabilizes, not all readers
+designed for a given minor version are backwards-compatible.
+
+(figure-2)=
+::::{card}
+```
+Header {
+  magic_number: uint8_t[4] = {0xFD, 0x2F, 0xC5, 0x30}
+  patch_version: uint16_t
+  minor_version: uint8_t
+  major_version: uint8_t
+  original_uncompressed_size: uint64_t
+  compressed_archive_size: uint64_t
+  reserved_padding1: uint64_t[4]
+  metadata_section_size: uint32_t
+  compression_type: uint16_t
+  reserved_padding2: uint16_t
+}
+```
++++
+**Figure 2**: Layout of the 64-byte archive header.
+::::
+
+The value in `compressed_archive_size` indicates the total size of the archive, including the size
+of the header. The `original_uncompressed_size` field indicates the total size of the data that was
+compressed into the archive. The interpretation of `original_uncompressed_size` changes somewhat
+based on what data was ingested into the archive. For example, when ingesting `ndjson`, the field
+records the number of bytes of raw JSON data ingested into the archive --- however, when ingesting
+KV-IR streams, the field records the number of decompressed bytes of KV-IR ingested into the archive
+(since KV-IR streams are typically compressed by a general purposed compressor before being stored).
+
+The `metadata_section_size` field indicates the _compressed_ size of the metadata section in bytes.
+This field can be used in combination with the `original_uncompressed_size` field and known header
+size to determine the size and offset of both the `metadata` and `files` sections.
+
+The compression type for an archive indicates the general-purpose compressor used to compress each
+section of the archive, and is currently one of:
+* `0x0000` - ZStandard
+
+All `reserved_padding` fields are reserved for use in future versions of the single-file archive
+format.
+
+## Metadata section
+
+The `metadata` section is made up of a compressed sequence of metadata packets encoded with the
+binary format shown in [Figure 3](#figure-3). Metadata packets generally contain information that
+relates to the entire archive or large sections of the archive.
+
+(figure-3)=
+::::{card}
+```
+MetadataPacket {
+  packet_type: uint8_t
+  packet_size: uint32_t
+  packet_content: uint8_t[packet_size]
+}
+
+MetadataPacketStream {
+  num_packets: uint8_t
+  packets: MetadataPacket[num_packets]
+}
+```
++++
+**Figure 3**: The `metadata` section packet stream binary format. The `metadata` section is
+equivalent to a single instance of `MetadataPacketStream`.
+::::
+
+Each metadata packet has a type, size, and arbitrary binary payload. Different packet types make
+different choices for encoding content in this binary payload. Since the size of each packet is
+well-defined, reader implementations can attempt to read archives containing packet types they are
+unfamiliar with by simply skipping the corresponding content. Generally, this metadata section
+design is intended to allow for some degree of forwards-compatibility and extensibility.
+
+Archives currently support the following metadata packet types, some of which are optional:
+* `0x00` - ArchiveInfo
+* `0x01` - ArchiveFileInfo
+* `0x02` - TimestampDictionary (optional)
+* `0x03` - RangeIndex (optional)
+
+### ArchiveInfo packet
+
+The ArchiveInfo packet is a msgpack map that currently only records the number of segments in an
+archive, as shown in [Figure 4](#figure-4). Each archive currently consists of only a single segment
+(i.e. there is only one tables segment file), but we still record the number of segments to offer
+backwards compatibility if we do start splitting tables into multiple segments.
+
+This metadata packet was originally intended to mimic the "ArchiveMetadata" structure in CLP, but
+most of what "ArchiveMetadata" records is now present in either the header or the RangeIndex
+metadata packet.
+
+(figure-4)=
+::::{card}
+```json
+{
+  "num_segments": 1
+}
+```
++++
+**Figure 4**: Layout of the ArchiveInfo msgpack payload.
+::::
+
+### ArchiveFileInfo packet
+
+The ArchiveFileInfo packet is a msgpack map that records the name and offset relative to the start
+of the `files` section of each entry in that section, as shown in [Figure 5](#figure-5). Entries
+are ordered by their offset into the `files` section. This means that the order of entries in the
+ArchiveFileInfo packet corresponds to the order in which the components of the `files` section
+should be read to avoid backwards seeks. The offsets stored in this section can be combined with
+information from the header to determine the size and absolute offset of every entry in the `files`
+section.
+
+(figure-5)=
+::::{card}
+```json
+{
+  "files": [
+    {
+      "n": "/schema_tree",
+      "o": 0
+    },
+    "..."
+  ]
+}
+```
++++
+**Figure 5**: Layout of the ArchiveFileInfo msgpack payload. The `"files"` array contains entries
+for each file in the `files` section, ordered by their offset. Each file is described by its name
+`"n"` and offset into the `files` section `"o"`.
+::::
+
+The ArchiveFileInfo packet has entries with the following names in order:
+* `"/schema_tree"` - the Merged Parse Tree
+* `"/schema_ids"` - the Schema Map
+* `"/table_metadata"` - metadata describing the contents of the tables segments
+* `"/var.dict"` - the Variable Dictionary
+* `"/log.dict"` - the Log-type Dictionary
+* `"/array.dict"` - the Array Log-type Dictionary (optional)
+* `"/0"` - the first tables segment
+
+The Array Log-type Dictionary is nominally optional for archives that use structured arrays, but in
+practice, when structured arrays are enabled, we just store an empty dictionary in this section.
+
+### TimestampDictionary packet
+
+The TimestampDictionary packet is a binary format that records:
+1. The key name, corresponding MPT nodes, and range of values for zero or more timestamp columns
+2. The format and ID of zero or more timestamp patterns used to encode timestamps in the archive
+
+The details of the binary format can be seen in [Figure 6](#figure-6).
+
+(figure-6)=
+::::{card}
+```
+enum EncodingType : uint64_t {
+  Epoch = 0x1,
+  DoubleEpoch = 0x2
+}
+
+TimestampRange {
+  key_len: uint64_t
+  key: char[key_len]
+  num_column_ids: uint64_t
+  column_ids: int32_t[num_column_ids]
+  encoding_type: EncodingType
+  epoch_start: union {epochtime_t, double}
+  epoch_end: union {epochtime_t, double}
+}
+
+TimestampPattern {
+  pattern_id: uint64_t
+  pattern_len: uint64_t
+  pattern: char[pattern_len]
+}
+
+TimestampDictionary {
+  num_ranges: uint64_t
+  ranges: TimestampRange[num_entries]
+  num_patterns: uint64_t
+  patterns: TimestampPattern[num_patterns]
+}
+
+```
++++
+**Figure 6**: TimestampDictionary binary payload format. The payload is equivalent to a single
+instance of "TimestampDictionary".
+::::
+
+The key name in each TimestampRange follows the same
+[escaping rules](../../user-guide/reference-json-search-syntax.md) we use for key names in KQL
+search. Note that we allow each key to map to multiple MPT nodes, and that each key's range can be
+recorded as either integer epoch time or double epoch time to handle timestamp columns with
+polymorphic types.
+
+The `pattern` in each TimestampPattern entry is a format string that follows the specification from
+the `clp_s::TimestampPattern` class. The associated `pattern_id` can be used to uniquely identify
+each format string. This allows string timestamps in the archive to be encoded as a tuple of epoch
+time and pattern id.
+
+### RangeIndex packet
+
+The archive range index allows users to associate arbitrary properties with each file (or any other
+unit of data) ingested into `clp-s`. Collectively, these units of data are referred to as "ingestion
+units". Since each archive can potentially aggregate data from multiple files, the archive range
+index associates these ingestion unit properties with a logical range of records in an archive.
+Note that ingestion units can be split across multiple archives in order to maintain a configured
+archive size, and that in these cases the properties become associated with each chunk of the
+ingestion unit in each archive.
+
+By default, we automatically store the following properties about each ingestion unit:
+* `"_filename"` - the original filename of the ingestion unit as it was passed to `clp-s` during
+compression
+* `"_file_split_number"` - incremented each time this ingestion-unit is split across another archive
+* `"_archive_creator_id"` - UUID associated with a particular _invocation_ of compression
+
+Currently `clp-s` will associate these default properties as well as any properties present in the
+metadata section of a KV-IR stream with each ingestion unit. There will likely be future support
+for associating arbitrary additional properties with an ingestion unit at compression time.
+
+The RangeIndex packet is encoded as a msgpack array with the format shown in [Figure 7](#figure-7).
+
+(figure-7)=
+::::{card}
+```json
+[
+  {
+    "s": 0,
+    "e": 100,
+    "f": {
+      "_filename": "/my/file.jsonl",
+      "_file_split_number": 0,
+      "_archive_creator_id": " 03f2958a-7a2e-448c-a203-60f2cc990d74",
+      "arbitrary_user_property": "..."
+    }
+  },
+  "..."
+]
+```
++++
+**Figure 7**: Layout of the RangeIndex msgpack payload. Each entry in the array records a start
+index `"s"` and end index `"e"` indicating that the properties correspond to the logical range of
+records `[s, e)`. No entries in the range index have overlapping logical ranges, and all entries are
+ordered by logical range. The `"f"` object contains the properties associated with an ingestion
+unit.
+::::
+
+Note that properties created and used by `clp-s` are always prefixed with the `_` character. To
+avoid naming collisions with properties created by `clp-s`, users should avoid creating properties
+with this prefix.
+
+## Files section
+
+### Merged parse tree
+
+### Schema map
+
+### Table metadata
+
+### Variable dictionary
+
+### Log-type dictionary
+
+### Array log-type dictionary
+
+### Table segments
+
+:::{warning}
+🚧 This section is still under construction.
+:::
+
+[s3-blog]: https://blog.yscope.com/optimizing-clp-for-s3-object-storage-b4c502e930ee
+[μSlope]: https://www.usenix.org/conference/osdi24/presentation/wang-rui
+[amazon-s3]: https://aws.amazon.com/s3/