Hi Xuneng, You're right that polling isn't ideal. For a backpatchable bug fix though, the trade-off seems reasonable: the change is contained in the walreceiver, doesn't touch the wire protocol, and applies to all back branches. Exploring better designs would be worthwhile but probably belongs in a separate effort.
Best regards, Marco On Fri, May 1, 2026 at 4:57 AM Xuneng Zhou <[email protected]> wrote: > Hi Marco, > > On Tue, Apr 28, 2026 at 12:50 AM Marco Nenciarini < > [email protected]> wrote: > >> v7 patches attached. No code changes from v6, just rebased on >> current master to remove minor offset, and the backpatch file is >> renamed with a "nocfbot-" prefix so the commitfest bot picks up >> only the master patch. >> >> >> On Mon, Apr 27, 2026 at 6:00 PM Marco Nenciarini < >> [email protected]> wrote: >> >>> Registered in PG20-1: https://commitfest.postgresql.org/patch/6716/ >>> >>> On Sat, Mar 21, 2026 at 11:52 AM Marco Nenciarini < >>> [email protected]> wrote: >>> >>>> Here are the v6 patches. >>>> >>>> Xuneng correctly pointed out that RequestXLogStreaming rounds down, >>>> not up, so it isn't the cause of the gap. The actual mechanism is >>>> that archive recovery processes whole segment files: after both nodes >>>> replay the same archived segment N, the cascade's next read position >>>> lands at the start of segment N+1, while the upstream's >>>> GetStandbyFlushRecPtr returns replayPtr inside segment N. >>>> >>>> Changes from v5: >>>> >>>> - Updated the code comment and commit message to describe the correct >>>> root cause (archive recovery segment granularity, not >>>> RequestXLogStreaming truncation). >>>> >>>> - Reset the catchup state when the upstream is no longer behind. >>>> Without this, if the walreceiver successfully streams, the >>>> connection breaks, and it loops back to find itself ahead again, >>>> the stale deadline from the previous wait would cause an immediate >>>> timeout. >>>> >>>> Two patches attached: v6-0001 for master (extends the >>>> walrcv_identify_system API) and v6-backpatch-0001 for stable branches >>>> (global variable to preserve ABI). >>>> >>> > Polling at intervals stil seems not good to me. But I don't have a better > idea for now. > > -- > Best, > Xuneng >
