Edouard Vanbelle
86d0d65583
`content_derived_blobs.variant` held the size alone, so one source could
hold exactly one artifact per size regardless of codec. That surfaced
when the read order flipped in 10c: a JPEG request matched the WebP row
and would have been served the wrong codec — hidden previously because
the .jpg sidecar won first. The flip had to be gated to WebP, which
meant JPEG clients could never leave the sidecar, which meant the
sidecar could never be deleted.
It blocks transcodes harder: those are multi-format by nature, so two
output codecs of one source collide on the primary key without a format
term.
The axis goes inside the string rather than into a fourth PK column,
per the column's own rule — "new axes go inside this string, never into
new columns". Shape is {size}.{ext}: preview.webp, icon.jpg, later
720p.webp.
The backfill is deterministic, not a guess: store_derived_blob has only
ever written "image/webp" for thumbnails. content_type is checked anyway
rather than assumed — a row that fails the assumption is left alone and
counted in a warning, because the read path then simply misses it and
falls back to the sidecar, whereas guessing a codec would serve wrong
bytes. Idempotent via NOT LIKE '%.%', so a re-apply cannot produce
preview.webp.webp; verified on a scratch PG by applying it twice.
One helper builds the string, because it is a primary-key component:
a writer and reader that disagree do not fail loudly, they just never
find each other's rows and the derived tier silently looks empty. It
lives on the service's ThumbnailSize, not the port's — they are distinct
types, which the compiler pointed out after I put it on the wrong one.
The WebP gate on the read path is now removed: each codec has its own
row, so JPEG can finally reach the derived tier — the prerequisite for
deleting the sidecar for those clients.
file_attached_blobs keeps a bare size: store_external_thumbnail
re-encodes everything to JPEG, so it is single-format by construction
and a format term would cost a migration for nothing.
57 lines
2.9 KiB
SQL
57 lines
2.9 KiB
SQL
-- Put the output format inside `variant`, where the plan says new axes go.
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--
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-- `content_derived_blobs.variant` held the size alone (`icon` | `preview` |
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-- `large`), so a size could hold exactly ONE stored artifact regardless of
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-- codec. That surfaced when the read order flipped (step 10c): a JPEG request
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-- matched the WebP row and would have been served the wrong codec, which the
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-- old ordering hid because the `.jpg` sidecar won first. The flip had to be
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-- gated to WebP, which in turn means JPEG clients can never leave the sidecar
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-- — so the sidecar can never be deleted.
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--
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-- It blocks transcodes harder still: those are multi-format by nature, so
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-- without a format term two output codecs of one source collide on the
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-- primary key.
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--
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-- Per the column's own comment — "new axes go inside this string, never into
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-- new columns" — the axis goes in the string rather than into a fourth PK
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-- column. The PK stays `(source_hash, kind, variant)`.
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--
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-- Shape: `{size}.{ext}` — `preview.webp`, `icon.jpg`, and later `720p.webp`
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-- for transcodes.
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--
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-- The backfill is deterministic rather than a guess: `store_derived_blob` has
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-- only ever been called with `"image/webp"` for thumbnails, so every existing
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-- thumbnail row is WebP. `content_type` is checked anyway rather than assumed
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-- — if that assumption is ever wrong, the row is left alone for a human to
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-- look at instead of being silently mislabelled.
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UPDATE storage.content_derived_blobs
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SET variant = variant || '.webp'
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WHERE kind = 'thumbnail'
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AND content_type = 'image/webp'
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-- Idempotent: skip anything already carrying a format suffix, so a
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-- re-applied migration cannot produce `preview.webp.webp`.
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AND variant NOT LIKE '%.%';
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-- Anything left without a format suffix did not match the WebP assumption.
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-- Surfaced as a warning rather than coerced: the read path will simply miss
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-- those rows and fall back to the sidecar, which is safe, whereas guessing a
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-- codec would serve the wrong bytes.
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DO $$
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DECLARE
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v_unsuffixed INT;
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BEGIN
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SELECT COUNT(*) INTO v_unsuffixed
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FROM storage.content_derived_blobs
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WHERE kind = 'thumbnail' AND variant NOT LIKE '%.%';
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IF v_unsuffixed > 0 THEN
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RAISE WARNING
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'derived_variant_encodes_format: % thumbnail row(s) have no format suffix (content_type was not image/webp). They will be ignored by the read path and re-derived on demand; inspect before deleting the sidecars.',
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v_unsuffixed;
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END IF;
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END $$;
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COMMENT ON COLUMN storage.content_derived_blobs.variant IS
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'Opaque discriminator carrying every axis but the source and the kind: size AND output format, as {size}.{ext} (preview.webp | icon.jpg | 720p.webp). New axes go inside this string, never into new columns. A format term is required — without one, two codecs of the same source collide on the primary key, and the read path cannot tell which codec a row holds.';
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