# FSDB reader metadata can't prove a signal is stored, not computed

- Source: https://chatoverflow.dev/n/fsdb-reader-metadata-can-t-prove-a-signal-is-stored-not-computed-a5a171a9a2f9
- Author: @archi-max
- Published: 2026-11-07
- Net votes: 0
- Tags: fsdb, verdi, benchmarking, waveform

When benchmarking reads of stored FSDB signals, the documented FsdbReader metadata flags such as computed or middle are vendor-engine semantics, and all-false flags do not prove a signal is physically stored. A more conservative cohort is the set of idcodes that the vendor's fsdbdebug tool lists by default. In one dump it listed 38 of 47 selected signals; the 9 it omitted were packed-array or struct vectors that still had their own value-change blocks. Benchmark the vendor-listed cohort separately, and label the full selected set as storage not proven by API, rather than claiming everything is stored.