docs(qwp): document C, C++, and Rust clients 7.1.0 and 7.2.0 - #589

Documents the C, C++, and Rust client behavior that shipped in c-questdb-client 7.1.0 and 7.2.0. Split out of #516, which keeps the Python changes until the Python client 5.1.0 is released.

Changes

• C/C++ and Rust client pages (7.1.0): UUID values cross the API in canonical RFC 4122 byte order, except the row-buffer call that takes the two 64-bit wire halves. Binary Arrow columns land as BINARY unless they claim UUID or LONG256 through arrow.uuid / questdb.column_type field metadata or a per-column override, with examples. A caution box covers the silent behavior change for code written against 7.0.0. Also documents the scope of in_doubt for low-level flushes and for Rust flush_polars_dataframe.
• C/C++ and Rust client pages (7.2.0): a QWP/WebSocket buffer flush must fit the frame cap, the smallest of max_buf_size, the server's advertised batch size, and the sf_max_segment_bytes segment payload capacity. line_sender_buffer_size / Buffer::len() is at least the encoded frame size, so applications can flush before reaching the cap. An oversized buffer fails with batch_too_large / ErrorCode::BatchTooLarge, publishes nothing, and keeps its rows. The C/C++ error table gains a batch_too_large row, including the in_doubt check for a chunk that queued some frames before failing.
• Store-and-forward: replay is at-least-once. A frame the server committed but did not acknowledge before a reconnect is written again; suppressing the duplicates needs table-level DEDUP UPSERT KEYS with stable row identity.
• QWP/WebSocket wire protocol: notes how the UUID wire encoding relates to RFC 4122 order and which client calls reverse it. The sentence lists C, C++, and Rust; docs(qwp): document canonical RFC 4122 UUID byte order #516 adds Python once 5.1.0 ships.
• Version references: the behavior-change notes name 7.1.0, the release that contains c-questdb-client#186, and the C/C++ FetchContent example pins the 7.2.0 tag.
• Changelog: entries for the above under October 2026.

Not covered

• 7.2.0 per-query reader timeouts (c-questdb-client#214). They need server support from feat(qwp): add per-query timeouts for queries over QWP questdb#7768, which no QuestDB release has yet; they will be documented once it ships.
• The standalone QWP/WebSocket sender changes in 7.2.0 (BatchTooLarge replacing InvalidApiCall, effective_frame_cap()). These pages document only the pooled API.

Related

• c-questdb-client#186 (UUID byte order and binary column claims), c-questdb-client#195 (in_doubt scope), c-questdb-client#227 (frame cap and buffer size)
• docs(qwp): document canonical RFC 4122 UUID byte order #516 (remaining Python 5.1.0 documentation)

Validation

• npm run build, which fails on broken links and anchors

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