David Clarke dclarke
dclarke
/ slide-03-04-histograms.promql
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May 1, 2026 06:24
When Metrics Lie - companion examples
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| # ============================================================================ | |
| # p99 histogram | |
| # ============================================================================ | |
| # WRONG: avg(p99) across pods. The hot pod's tail is averaged out. | |
| # avg by (service) ( | |
| # histogram_quantile(0.99, rate(http_request_duration_seconds_bucket[5m])) | |
| # ) | |
| # | |
| # RIGHT: sum the _bucket counts across instances first, then quantile. | |
| # Use a recording rule so dashboards consume the rolled-up series. |
dclarke
/ slide-03-04-histograms.promql
Created
May 1, 2026 00:37
When Metrics Lie - companion examples
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| # ============================================================================ | |
| # p99 histogram | |
| # ============================================================================ | |
| # WRONG: avg(p99) across pods. The hot pod's tail is averaged out. | |
| # avg by (service) ( | |
| # histogram_quantile(0.99, rate(http_request_duration_seconds_bucket[5m])) | |
| # ) | |
| # | |
| # RIGHT: sum the _bucket counts across instances first, then quantile. | |
| # Use a recording rule so dashboards consume the rolled-up series. |
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| localhost:mochitest dclarke$ python runtestsb2g.py --b2gpath /Volumes/Boot2Gecko/B2G/ --xre-path /Volumes/Boot2Gecko/mozilla-central/obj-x86_64-apple-darwin12.3.0/dist/bin/ --console-level INFO --emulator arm --test-path tests/dom/apps/tests/test_packaged_app_install.html | |
| waiting for system-message-listener-ready... | |
| done | |
| args: ['/Volumes/Boot2Gecko/mozilla-central/obj-x86_64-apple-darwin12.3.0/dist/bin/xpcshell', '-g', '/Volumes/Boot2Gecko/mozilla-central/obj-x86_64-apple-darwin12.3.0/dist/bin', '-v', '170', '-f', './httpd.js', '-e', "const _PROFILE_PATH = '/var/folders/zg/gwxjd1ss2nl3jktt5khghk540000gn/T/tmpOHSnBh';const _SERVER_PORT = '8888'; const _SERVER_ADDR = '127.0.0.1';\n const _TEST_PREFIX = undefined; const _DISPLAY_RESULTS = false;", '-f', './server.js'] | |
| INFO | runtests.py | Server pid: 61009 | |
| INFO | runtests.py | Websocket server pid: 0 | |
| INFO | runtests.py | Running tests: start. | |
| INFO | runtests.py | Received unexpected exception while running application | |
| Traceback (most recent |
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| // make operations on the table asynchronous, for performance | |
| mDBConn->ExecuteSimpleSQL(NS_LITERAL_CSTRING("PRAGMA synchronous = OFF")); | |
| // cache frequently used statements (for insertion, deletion, and updating) | |
| rv = mDBConn->CreateAsyncStatement(NS_LITERAL_CSTRING( | |
| "INSERT INTO moz_hosts " | |
| "(id, host, type, permission, expireType, expireTime, appId, isInBrowserElement) " | |
| "VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8)"), getter_AddRefs(mStmtInsert)); | |
| NS_ENSURE_SUCCESS(rv, rv); |