[TASK-429] Pre-size Arrow builders and recommend jemalloc for write path

[fresh-borzoni]

Summary

close #429

• Pre-size Arrow builders to DEFAULT_MAX_RECORD (256) capacity to eliminate reallocations
• Document jemalloc as recommended allocator for Linux deployments
• Add jemalloc setup to examples

Benchmark results (Linux, glibc, 8 threads, 100K cycles, 13-column schema)

Variant	Throughput	RSS delta
Default capacity raw Arrow	baseline	baseline
Pre-sized raw Arrow	+30%	-15%
Pre-sized fluss builder	+4%	-12%
jemalloc + pre-sized	+45% vs default	-25%

I will address these findings during benchmarking in

Follow-ups

• Switch DEFAULT_MAX_RECORD hard cap to byte-size #431
• Replace FieldGetter/Datum dispatch with typed column writers #432

[fresh-borzoni]

@luoyuxia @leekeiabstraction PTAL 🙏

[leekeiabstraction]

TY for the PR, left some comments

[fresh-borzoni]

@leekeiabstraction Addressed magic number, PTAL 🙏

[leekeiabstraction]

Approved, TY for the PR

[Copilot]

Pull request overview

This PR implements two performance optimizations for the write path: pre-sizing Arrow column builders to DEFAULT_MAX_RECORD (256) capacity to eliminate growth reallocations, and documenting jemalloc (tikv-jemallocator) as the recommended allocator for production Linux deployments with an accompanying example setup.

Changes:

• Pre-size all Arrow column builders (with_capacity instead of new) in RowAppendRecordBatchBuilder::create_builder, using a fixed capacity of 256 and a 64-byte average data buffer for variable-width types.
• Add jemalloc documentation to the crate-level doc comment in lib.rs and configure it in the examples crate (Cargo.toml + example_table.rs).
• Remove a stray blank line in crates/fluss/Cargo.toml.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
crates/fluss/src/record/arrow.rs	All Arrow builders now use with_capacity(256) instead of new(); variable-width types also pre-allocate data buffers; create_builder updated with a capacity parameter.
crates/fluss/src/lib.rs	Crate-level doc comment expanded with a # Performance section recommending jemalloc for Linux production use.
crates/examples/Cargo.toml	Adds tikv-jemallocator = "0.6" as a conditional dependency for non-MSVC targets.
crates/examples/src/example_table.rs	Activates jemalloc as #[global_allocator] for the example binary.
crates/fluss/Cargo.toml	Removes trailing blank line in dev-dependencies section.

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[fresh-borzoni]

Addressed comments

[fresh-borzoni]

fixed ci/cd, example_table.rs includes the other two files as mod, so we don't need to add global allocator separately

[luoyuxia]

@fresh-borzoni Thanks for the improvement. LGTM