interconnect: prune cursor IC history table by local xid, not distributed xid - #1964
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interconnect: prune cursor IC history table by local xid, not distributed xid#1964yjhjstz wants to merge 1 commit into
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…uted xid SetupUDPIFCInterconnect_Internal() records one CursorICHistoryEntry per interconnect instance on the QD and prunes old entries only when the statement runs in a different transaction than the previous one, using the distributed xid as the transaction identity. Distributed xids are assigned lazily (only for transactions that write or are dispatched two-phase), so autocommit read-only statements always see InvalidDistributedTransactionId on both sides of the comparison. The table is therefore never pruned on read-only sessions and grows by one 48-byte entry per Motion-containing statement for the life of the backend (2.8 MB after 60000 statements, plus the heap fragmentation the steady stream of small long-lived allocations induces). Use MyProc->lxid instead: it is assigned to every top-level transaction, including read-only ones, and stays constant within a transaction block, so entries belonging to cursors that are still open in the current transaction remain protected exactly as before. Verified on a single long-lived session running the queries from apache#1947: UdpInterconnectMemContext grew 0 -> 2814 KB over 60000 statements before the change and stays at 12 KB after it; RssAnon went 12.7 -> 24.6 MB before and is flat at 14.4 MB after. Pruning still does not happen inside an explicit transaction block or while a cursor is open, and FETCH from an open cursor after 300 intervening statements works. Related: apache#1947
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SetupUDPIFCInterconnect_Internal() records one CursorICHistoryEntry per interconnect instance on the QD and prunes old entries only when the statement runs in a different transaction than the previous one, using the distributed xid as the transaction identity. Distributed xids are assigned lazily (only for transactions that write or are dispatched two-phase), so autocommit read-only statements always see InvalidDistributedTransactionId on both sides of the comparison. The table is therefore never pruned on read-only sessions and grows by one 48-byte entry per Motion-containing statement for the life of the backend (2.8 MB after 60000 statements, plus the heap fragmentation the steady stream of small long-lived allocations induces).
Use MyProc->lxid instead: it is assigned to every top-level transaction, including read-only ones, and stays constant within a transaction block, so entries belonging to cursors that are still open in the current transaction remain protected exactly as before.
Verified on a single long-lived session running the queries from #1947: UdpInterconnectMemContext grew 0 -> 2814 KB over 60000 statements before the change and stays at 12 KB after it; RssAnon went 12.7 -> 24.6 MB before and is flat at 14.4 MB after. Pruning still does not happen inside an explicit transaction block or while a cursor is open, and FETCH from an open cursor after 300 intervening statements works.
Fixes #1947
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make installcheckmake -C src/test installcheck-cbdb-parallelImpact
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