Three reversals had landed without the documentation following them, so the
docs described a pipeline that compresses its output, a schema with three
secondary indexes, and a browser that re-downloads the file on every visit.
None of those are true any more.
- Compression: the assembler stopped producing .gz when the databases began
shipping as .sqlite3. The deployment guide's "why no uncompressed database
can ship" section explained a guard that now exists for the opposite reason
— to keep .db, .gz and journals out, so .sqlite3 stays the only name.
- Indexes: the architecture printed a DDL with three CREATE INDEX statements
and a paragraph on the partial one. schema.go carries none.
- Persistence: "the download is repeated every visit ... has not been done"
was listed as an open risk after db-cache.js closed it. Replaced with the
ETag flow, the offline fallback, and the risks that did replace it.
Measured both transfers rather than scaling one from the other, which would
have been wrong: 2016 is 142 MB stored and 31 MB delivered, 2017 is 119 MB and
36 MB. The smaller database is the larger download, so neither figure follows
from the stored size.
Also corrects a CHUNK_BYTES reference to a module that no longer exists, the
238-289 MB per-dataset figure, two paths to web/src/lib/datasets.js, and the
CI step list, which omitted npm test and the post-deploy header check.
The two code comments that said the same outdated things go with them.
Two caches, one on each side.
In the browser, the response is stored in Cache Storage keyed by the
server's ETag, so the transfer is paid once per device rather than once
per visit. A stored copy opens without the gate: consent was given the
first time and reuse costs no network. A redeploy changes the ETag, so
the new version replaces the old instead of answering with last week's
data, and every older version of that database is dropped so one dataset
never occupies the disk twice. When the server cannot be reached at all,
any stored version is used, which incidentally makes the site work
offline. Storing is best effort — a full disk means downloading again
next time, which is no reason to fail the page.
The response is cached from a clone while the original is read for the
progress bar, rather than buffering the file a second time in the one
place where memory is already the binding constraint.
In CI, the built databases are cached on the inputs that determine them:
data/**, parser/** and datasets.json. Parsing 348 MB of spreadsheets is
the slow part of the job, and a web or docs change cannot alter a
database, so those pushes restore instead of rebuilding. Exact matches
only — no restore-keys, since a near-miss would publish databases built
from inputs the commit does not describe.
Reading the file where it lay never worked well enough. Two costs were
structural rather than bugs: reads are serial, because the worker uses
synchronous XHR, so a name search touching 390 pages waited 17 seconds
to move 608 KB — roughly one request per result row, which no page size
removes — and the first visitor after each deploy waited ~26 seconds for
the CDN to fill its cache with a 288 MB object.
The browser now downloads the whole database once and queries it in
memory with sql.js. A dataset page is gated behind that: the gate states
what it will cost, in transfer and in memory, and offers only the
download, because there is nothing to show without it.
Dropping the structures that existed to make range-request queries
index-driven halved the file. name_word carried one row per word of
every name, about 3.5 million of them, and with the partial score
indexes it was more than half of what every visitor would now download.
Measured on rebuilt databases: 2016 went 288.6 -> 142.5 MB (31 MB
gzipped on the wire), 2017 237.7 -> 119.3 MB, both with row counts and
audits unchanged. Queries on the result: an exam number is immediate, a
name scans all 877,460 rows in about 240 ms.
Alternatives were measured before choosing this. sqlite-wasm-http sizes
files from a HEAD Content-Length with no override, so on a host that
gzips it silently uses the compressed size. DuckDB-WASM ships 32-37 MB
of WebAssembly before its Parquet extension, more than this whole
download. Static pre-generated shards are the most robust option but
cannot answer arbitrary SQL, and cannot stop early the way LIMIT does.
The published name loses its chunk index, the byte budgets and the SQL
consent modal go with the range reads that made them necessary, and the
docs no longer describe a design the site does not use.
The previous attempt passed fileLength in the inline config, and the
worker discarded it. sqlite.worker.ts builds the lazy file's config
itself and hardcodes:
fileLength: config.serverMode === "chunked"
? config.databaseLengthBytes
: undefined
So in full mode there is no way to supply a length, and the library
falls back to sizing the file with a HEAD request — which GitHub Pages
answers with the gzipped length, and then refuses to use.
Chunked mode is the only mode that takes a length. One chunk holds the
whole database, so the chunk index is always 0 and every request goes to
urlPrefix + "0"; the assembler therefore publishes <id>.sqlite30. The
length still comes from the range probe, which also checks the bytes are
a SQLite header.
dbPrefixOf and dbOf derive one form from the other and are handed to
RemoteDatabase together, so the prefix the library appends an index to
and the file the assembler writes cannot drift apart. A test pins that;
nothing else would catch it, because the symptom is a 404 per query.
The stray-artifact guard now also rejects a leftover <id>.sqlite3, which
after this change is a stale artifact rather than the published one.
sqlite-wasm-http was checked as an alternative and does not help: its
worker takes the size from a HEAD Content-Length too, and its options
expose no way to override it, so on Pages it would silently use the
compressed size. Its shared-cache backend wants COOP/COEP, but it ships
a fallback that does not, so isolation was never the blocker — the
architecture note claiming otherwise is corrected.
The previous attempt passed fileLength in the inline config, and the
worker discarded it. sqlite.worker.ts builds the lazy file's config
itself and hardcodes:
fileLength: config.serverMode === "chunked"
? config.databaseLengthBytes
: undefined
So in full mode there is no way to supply a length, and the library
falls back to sizing the file with a HEAD request — which GitHub Pages
answers with the gzipped length, and then refuses to use.
Chunked mode is the only mode that takes a length. One chunk holds the
whole database, so the chunk index is always 0 and every request goes to
urlPrefix + "0"; the assembler therefore publishes <id>.sqlite30. The
length still comes from the range probe, which also checks the bytes are
a SQLite header.
dbPrefixOf and dbOf derive one form from the other and are handed to
RemoteDatabase together, so the prefix the library appends an index to
and the file the assembler writes cannot drift apart. A test pins that;
nothing else would catch it, because the symptom is a 404 per query.
The stray-artifact guard now also rejects a leftover <id>.sqlite3, which
after this change is a stale artifact rather than the published one.
sqlite-wasm-http was checked as an alternative and does not help: its
worker takes the size from a HEAD Content-Length too, and its options
expose no way to override it, so on Pages it would silently use the
compressed size. Its shared-cache backend wants COOP/COEP, but it ships
a fallback that does not, so isolation was never the blocker — the
architecture note claiming otherwise is corrected.
GitHub Pages serves .sqlite3 as application/octet-stream, which mime-db
marks compressible, so an un-ranged response comes back gzipped with the
compressed length. sql.js-httpvfs sizes a file with a HEAD request, sees
that length is unusable and refuses to open the database:
Length of the file not known. It must either be supplied in the config
or given by the HTTP server.
Page reads were never affected. The Fetch standard requires browsers to
send Accept-Encoding: identity on any request carrying a Range header,
and the live site returns 206 with raw bytes to one. So the length is
probed the same way and passed as fileLength, which is the escape hatch
the library's own message points at.
The probe reads the first 100 bytes, so it also checks the file starts
with the SQLite magic and that its page size matches the request size —
a host that ever compresses a ranged response now fails with a clear
message rather than feeding the library the wrong bytes.
The post-deploy check the docs prescribed could not have caught this: a
bare `curl -sI` advertises no encoding, so it reports success whatever
the host does. It is replaced, in the docs and in CI, by a ranged read
that verifies the bytes.
Every .ts becomes .js, every lang="ts" becomes lang-less, and the type
declarations go with them: types.ts held nothing but types, so it is
deleted outright.
Tooling follows. typescript, svelte-check, typescript-eslint and
@types/sql.js are uninstalled; tsconfig.json becomes jsconfig.json, which
still extends the generated SvelteKit config so $lib and $app resolve in
an editor; `npm run lint` is now ESLint alone, and CI's comment about it
covering the type check goes too.
What this gives up, stated plainly: a mistyped column name like
row.nguvan used to fail the build and now renders blank, and the
datasets.json-to-CONTENT cross-check is back to throwing at module load
rather than at compile time. The runtime guard for the latter is still
there and still throws loudly.
Two mechanical notes. The svelte/no-navigation-without-resolve rule
started flagging the footer's source link, which points at an off-site
article — without type information the rule can no longer tell an
external URL from a route, so that one line carries a disable comment.
And Vitest's include pattern had to follow the tests to .js.
Lint, 25 tests and the build all pass.
The browser downloaded 45 MB of gzipped SQLite before it could answer
anything. Now sql.js-httpvfs asks for the pages a query touches and the
databases ship uncompressed as <id>.sqlite3 — a byte range of a gzip
stream is not a byte range of a database.
That only works if every query the site issues is index-driven, and
measured against the real 2016 file, most were not:
so_bao_danh = ? SEARCH via PK ~20 KB
ho_ten_ascii LIKE '%x%' SCAN 127 MB
ho_ten_ascii LIKE 'x%' SCAN 127 MB
COUNT(*) covering index scan 20 MB
ORDER BY toan DESC LIMIT 10 SCAN + temp b-tree 127 MB
Prefix LIKE scans because SQLite's LIKE optimisation needs a NOCASE
index; a range comparison does use the index. So the schema changed to
suit the access pattern rather than the search changing to suit the
schema.
name_word holds one row per word of each name, WITHOUT ROWID so the
table is the index, carrying ho_ten_ascii so a multi-word query is
resolved inside a single b-tree. name_word_freq says which word of a
query is rarest — the vocabulary is 4,397 words across 2.87M entries, so
"buu loc" seeks on 287 entries rather than walking the 300,000 that
"thi" would. Searching by any word of a name survives, at a few hundred
KB a query.
idx_ho_ten and idx_ho_ten_ascii are gone: no plan could use either.
Partial indexes on toan, khtn and khxh cost 12 MB and keep the SQL
presets off a full scan. The footer's candidate count now comes from
datasets.json instead of COUNT(*).
2016 grows 223.5 MB to 288.6 MB, 2017 162.7 MB to 237.7 MB, and the site
is 528 MB against the 1 GB GitHub Pages limit. Row counts are unchanged.
The SQL tab is the one place a user can still write a query that reads
the whole table, so it asks before it opens, runs under a byte budget
that stops a runaway query, and shows what each query actually fetched.
Verified: row counts through the assembler guards, every app query
index-driven under EXPLAIN QUERY PLAN, and GitHub Pages returning 206
with a correct Content-Range. Not verified in a browser — this machine
has none — and the library refuses to open a file the host compresses,
so the deployed response headers need a look.
The app was a single-entry React SPA: one index.html that the assembler
copied to every dataset path, with a hand-rolled router resolving the
dataset from window.location and the title patched in at runtime because
one file had to serve every route.
SvelteKit prerenders a real page per route instead. The entry generator
in routes/[dataset]/+page.ts reads the same datasets.json the assembler
does, so the set of pages and the set of databases cannot drift apart,
and each dataset page ships its own <title> and description.
Everything framework-free moved across unchanged in behaviour and became
typed: the admission blocks, subject list, query classifier and SQL
presets. `Student` now mirrors the 22-column table, so a mistyped column
name fails the build rather than rendering blank.
Tailwind replaces the stylesheet. Theme tokens are CSS variables, which
keeps dark mode a single block of overrides rather than a `dark:` variant
on every class. The score tiers stay hand-written CSS: the class is
chosen at runtime from a score, and no utility generator can see that.
Adds the tests the frontend never had, over the three modules where a
silent wrong answer is possible — most importantly that toAscii here
folds exactly as ToAscii does in the parser, which is what makes
accent-insensitive search find anything.
The assembler stops copying index.html per dataset and checks that the
build prerendered each one instead. The database presence, raw-artifact
and idempotence guards are untouched.
Verified: 25 tests, ESLint and svelte-check clean, and a full
`assemble site` producing /thptqg/, /thptqg/2016/, /thptqg/2017/ and
404.html with absolute asset URLs. Not verified in a browser — this
machine has none.
Four of the 119 files in data/2016 publish one score column per subject
instead of a DIEM_THI sentence, and none of them was being read correctly.
The ĐH Công nghiệp Thực phẩm file puts a three-row ministry title block
above its header, so no header was recognised and the positional fallback
shifted every column by one: the serial number became so_bao_danh, the
exam number became ho_ten, the name became ngay_sinh, and the national ID
became the score cell. All 7,833 rows were unusable. The three ĐH Cần Thơ
files name an SBD column but no DIEM_THI, so they fell to the same
fallback: surname into ngay_sinh, given name into ten_cum_thi, birth date
into the score cell, and 12,152 candidates with no scores at all.
Both are now read by FormatSubjectColumns, which resolves identity and one
column per subject from the header. The header is searched for in the
first five rows, so a title block no longer hides it.
The Cần Thơ score columns are numbered rather than named. They follow the
order the exam was sat — each morning an essay paper, each afternoon a
multiple-choice one — which is what identifies them: columns 1/3/5/7
quantise to 0.25 and 2/4/6/8 do not, and each column's mean lands within
0.5 of the same subject's mean across the rest of the dataset. The
foreign language is filed under the subject its N1..N6 code names.
Gender now accepts the 0/1 encoding those files use: of the rows marked
1, 53% carry "Thị" in the name against 1% of those marked 0. Birth dates
in the compact ddmmyy form are expanded so the column holds one format.
A score of 0 is stored rather than dropped, recovering 302 real scores
that a JavaScript falsy check had been turning into NULL.
Row count falls by one, to 877,460: the removed row is the title line
"ĐƠN VỊ: / TRƯỜNG ĐẠI HỌC CÔNG NGHIỆP THỰC PHẨM TP. HỒ CHÍ MINH", which
had been stored as a student. The dataset has no duplicate exam numbers;
the three rows previously described as collapsing were that same file's
title and header lines being counted and then rejected.
Also drops behaviour that existed only to match the parser this one
replaced: the inert "SINH " header token, the untrimmed diem_thi cell, an
unreachable blank-row branch, and a cross-check test against a database
that can no longer exist. None of them changes output.
Verified by rebuilding both datasets: 877,460 and 861,068 rows, both
artifacts through the assembler's row and size guards, and the reader
fidelity suite unchanged across all 182 files.
Routine verification is parser and assembler. The crawler is not part of the
build — data/<id>/ is committed and a crawl only refreshes it by hand — so its
tests do not gate ordinary changes, though CI still runs all three.
Also records the constraints that read as mistakes and get "fixed": the
verbatim data/2016/ filenames that decide duplicate-SBD resolution, the frozen
reader oracle, the literal combining-mark range ToAscii must share with the
site, the absolute Vite base, and dbSizeMb doubling as a truncation guard.
tiennm99