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Chris LuandGitHub
d867b6e739
The queue holds sixteen sealed windows, which is a memory bound only while a window is BufferSize. An entry larger than that grows its window to fit, and the depth then multiplies straight through: sixteen queued copies of a 100 MB window is 1.6 GB of flush data alone. Account the queued bytes and make producers wait once they pass the ceiling the depth was chosen for. What is charged is the pooled slab rather than the window length, since mem.Allocate rounds up to a size class and the queue holds the whole slab. A window larger than the whole budget still goes through on its own, so an oversized entry is never stuck. Windows are admitted in the order they were sealed. A producer can now park here for seconds, and letting a later window overtake an earlier one would persist them out of order and walk lastFlushedOffset and lastFlushTsNs backwards. A window is copied into its slab under the write lock, before the reservation is taken, so a burst of concurrent oversized writers would each hold a full copy in hand while queueing up -- memory the budget never sees. Large writers wait for queue headroom before they take the lock, which throttles the burst; it does not bound it, since a writer that passes the check still seals unconditionally. Take any room in the queue before the shutdown escape, too: the window is already sealed by then, so dropping it loses records the caller was told were accepted. A shutdown that races a full queue can still drop one -- that predates this change and needs the flush loop's lifetime reworked. Size a grown window to the entry rather than to twice it: the extra room only bought space for a second oversized record in the same window, which doubles the flush copy and the snapshot taken of it. The overflow guard halved its bound for that doubled allocation, so raise it to match what is now allocated and what maxBufferSize documents.