diff options
Diffstat (limited to 'src/backend/commands/copy.c')
| -rw-r--r-- | src/backend/commands/copy.c | 58 |
1 files changed, 53 insertions, 5 deletions
diff --git a/src/backend/commands/copy.c b/src/backend/commands/copy.c index 57c35bd6aa0..4f04d122c30 100644 --- a/src/backend/commands/copy.c +++ b/src/backend/commands/copy.c @@ -2715,15 +2715,63 @@ CopyFrom(CopyState cstate) RelationGetRelationName(cstate->rel)))); } - /* - * If the target file is new-in-transaction, we assume that checking FSM - * for free space is a waste of time. This could possibly be wrong, but - * it's unlikely. + /*---------- + * Check to see if we can avoid writing WAL + * + * If archive logging/streaming is not enabled *and* either + * - table was created in same transaction as this COPY + * - data is being written to relfilenode created in this transaction + * then we can skip writing WAL. It's safe because if the transaction + * doesn't commit, we'll discard the table (or the new relfilenode file). + * If it does commit, we'll have done the table_finish_bulk_insert() at + * the bottom of this routine first. + * + * As mentioned in comments in utils/rel.h, the in-same-transaction test + * is not always set correctly, since in rare cases rd_newRelfilenodeSubid + * can be cleared before the end of the transaction. The exact case is + * when a relation sets a new relfilenode twice in same transaction, yet + * the second one fails in an aborted subtransaction, e.g. + * + * BEGIN; + * TRUNCATE t; + * SAVEPOINT save; + * TRUNCATE t; + * ROLLBACK TO save; + * COPY ... + * + * Also, if the target file is new-in-transaction, we assume that checking + * FSM for free space is a waste of time, even if we must use WAL because + * of archiving. This could possibly be wrong, but it's unlikely. + * + * The comments for table_tuple_insert and RelationGetBufferForTuple + * specify that skipping WAL logging is only safe if we ensure that our + * tuples do not go into pages containing tuples from any other + * transactions --- but this must be the case if we have a new table or + * new relfilenode, so we need no additional work to enforce that. + * + * We currently don't support this optimization if the COPY target is a + * partitioned table as we currently only lazily initialize partition + * information when routing the first tuple to the partition. We cannot + * know at this stage if we can perform this optimization. It should be + * possible to improve on this, but it does mean maintaining heap insert + * option flags per partition and setting them when we first open the + * partition. + * + * This optimization is not supported for relation types which do not + * have any physical storage, with foreign tables and views using + * INSTEAD OF triggers entering in this category. Partitioned tables + * are not supported as per the description above. + *---------- */ + /* createSubid is creation check, newRelfilenodeSubid is truncation check */ if (RELKIND_HAS_STORAGE(cstate->rel->rd_rel->relkind) && (cstate->rel->rd_createSubid != InvalidSubTransactionId || - cstate->rel->rd_firstRelfilenodeSubid != InvalidSubTransactionId)) + cstate->rel->rd_newRelfilenodeSubid != InvalidSubTransactionId)) + { ti_options |= TABLE_INSERT_SKIP_FSM; + if (!XLogIsNeeded()) + ti_options |= TABLE_INSERT_SKIP_WAL; + } /* * Optimize if new relfilenode was created in this subxact or one of its |