{"id":41,"date":"2026-10-03T16:33:40","date_gmt":"2026-10-03T16:33:40","guid":{"rendered":"https:\/\/hoho.live\/luda\/index.php\/2026\/10\/03\/how-loki-query-responses-are-gzipped-on-the-way-to-a-log-viewer\/"},"modified":"2026-10-04T09:48:27","modified_gmt":"2026-10-04T01:48:27","slug":"how-loki-query-responses-are-gzipped-on-the-way-to-a-log-viewer","status":"publish","type":"post","link":"https:\/\/hoho.live\/luda\/index.php\/2026\/10\/03\/how-loki-query-responses-are-gzipped-on-the-way-to-a-log-viewer\/","title":{"rendered":"How Loki query responses are gzipped on the way to a log viewer"},"content":{"rendered":"\n

Short answer:<\/strong> Loki gzips query_range<\/code> when frontend.compress_responses<\/code> is true and the client sends Accept-Encoding: gzip<\/code>. On 3.4.2 the help text for -querier.compress-http-responses<\/code> says that default is true. It is not the value the process runs with. RegisterFlags<\/code> then registers -frontend.support-parquet-encoding<\/code> on that same bool, with default false, so gzip stays off until the YAML key is set. That second registration is a bug. It is still there in 3.6.17 and 3.7.8. Main corrects it in #23885<\/a>, which those releases do not contain.<\/p>\n\n\n

\n\n

What query_range returns<\/strong><\/h4>\n\n

GET \/loki\/api\/v1\/query_range<\/code> returns JSON. With compress_responses<\/code> true and Accept-Encoding: gzip<\/code>, the body is gzip and the response carries Content-Encoding: gzip<\/code> and Vary: Accept-Encoding<\/code>. A short body stays plain JSON and has no Content-Encoding<\/code>.<\/p>\n\n\n

In pkg\/lokifrontend\/config.go<\/code> the first BoolVar<\/code> points -querier.compress-http-responses<\/code> at compress_responses<\/code> and sets it true. The next BoolVar<\/code> points -frontend.support-parquet-encoding<\/code> at that same field and sets it false. Go writes a flag’s default into the variable when the flag is registered, so the second call wins. -help<\/code> still prints the first flag’s own default, true. The support_parquet_encoding<\/code> field is never attached to its flag.<\/p>\n\n\n

A config file that omits the key leaves the field false. On 3.4.2 the expanded config showed compress_responses: false<\/code>, and the same query came back as plain JSON. Setting the key and restarting produced gzip. Read the expanded config after the reload.<\/p>\n\n\n

One 500-line query_range<\/code> was 103,278 bytes as identity and 10,655 bytes as gzip.<\/p>\n\n\n

The push is a different body. Promtail’s default POST to \/loki\/api\/v1\/push<\/code> is snappy-compressed protobuf. This flag does not change that POST.<\/p>\n\n\n

\n\n

What the client does with the body<\/strong><\/h4>\n\n

A Go net\/http<\/code> client that does not set Accept-Encoding<\/code> itself asks for gzip and decompresses before the application reads the body. Grafana’s datasource is in that class, so turning the key on does not break it.<\/p>\n\n\n

Python’s urllib<\/code> does not. If the request sets Accept-Encoding: gzip<\/code>, urlopen<\/code> returns the compressed bytes. json.load<\/code> on that body fails. Decompress only when Content-Encoding<\/code> is gzip, then parse. A response with no such header is already JSON.<\/p>\n\n\n

\n\n

The working path<\/strong><\/h4>\n\n
    \n
  1. On 3.4.2 through 3.7.8, set frontend.compress_responses: true<\/code>.<\/li>\n
  2. Reload the process and read the expanded config. The field has to say true.<\/li>\n
  3. Call query_range<\/code> with Accept-Encoding: gzip<\/code>.<\/li>\n
  4. If Content-Encoding<\/code> is gzip, decompress, then parse JSON. If the header is absent, parse the bytes as JSON.<\/li>\n<\/ol>\n\n\n

    #23885<\/a> binds -frontend.support-parquet-encoding<\/code> to support_parquet_encoding<\/code>. A binary that contains that change keeps the documented default, and the YAML key is optional.<\/p>\n\n\n

    \n\n

    Approaches that look simpler and fail<\/strong><\/h4>\n\n
    \n\n\n\n\n\n\n\n
    Approach<\/th>\nWhy it fails<\/th>\n<\/tr>\n<\/thead>\n
    Trust -help<\/code> once the flags have been registered<\/td>\nThe parquet flag is registered on compress_responses<\/code> and writes false<\/td>\n<\/tr>\n
    json.load<\/code> the body after Python urllib sends Accept-Encoding: gzip<\/code><\/td>\nurllib does not decompress. The first bytes are the gzip header<\/td>\n<\/tr>\n
    Wait for a 3.6 or 3.7 release<\/td>\n3.6.17 and 3.7.8 still register the parquet flag on compress_responses<\/code><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n\n\n

    -help<\/code> prints each flag’s own default. The expanded config is the value the process uses.<\/p>\n\n\n

    \n\n

    When you can omit the key<\/strong><\/h4>\n\n

    Omit frontend.compress_responses<\/code> on a build that contains #23885. That is a source change, not a switch inside 3.4.2. Until the binary has that registration, set the key.<\/p>\n\n\n

    \n\n

    Why this stays published<\/strong><\/h4>\n\n

    We hit this on Loki 3.4.2: query_range<\/code> answered with plain JSON while the flag help said gzip was on. The parquet flag is registered on compress_responses<\/code> and clears it. Set frontend.compress_responses: true<\/code> until the binary contains the #23885 fix.<\/strong><\/p>\n\n\n

    \u672c\u6587\u7531 HoHo \u8207 AI \u5354\u4f5c\u6574\u7406\uff0c\u6700\u5f8c\u66f4\u65b0\u65bc 2026 \u5e74 10 \u6708 4 \u65e5\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

    Short answer: Loki gzips query_range when frontend.compress_responses is true and the client sends Accept-Encoding: gzip. On 3.4.2 the help text for -querier.compress-http-responses says that default is true. It is not the value the process runs with. RegisterFlags then registers -frontend.support-parquet-encoding on that same bool, with default false, so gzip…<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7,17,19],"tags":[21,20,14],"class_list":["post-41","post","type-post","status-publish","format-standard","hentry","category-homelab","category-logging","category-loki","tag-grafana","tag-gzip","tag-loki"],"_links":{"self":[{"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/posts\/41","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/comments?post=41"}],"version-history":[{"count":2,"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/posts\/41\/revisions"}],"predecessor-version":[{"id":52,"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/posts\/41\/revisions\/52"}],"wp:attachment":[{"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/media?parent=41"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/categories?post=41"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/hoho.live\/luda\/index.php\/wp-json\/wp\/v2\/tags?post=41"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}