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authorRobert Haas <rhaas@postgresql.org>2015-04-30 15:02:14 -0400
committerRobert Haas <rhaas@postgresql.org>2015-04-30 15:02:14 -0400
commit924bcf4f16d54c55310b28f77686608684734f42 (patch)
tree79f35bf679c6a68dbe725cc90248a553f2b9e019 /src/backend/access/transam/xlog.c
parent669c7d20e6374850593cb430d332e11a3992bbcf (diff)
downloadpostgresql-924bcf4f16d54c55310b28f77686608684734f42.tar.gz
postgresql-924bcf4f16d54c55310b28f77686608684734f42.zip
Create an infrastructure for parallel computation in PostgreSQL.
This does four basic things. First, it provides convenience routines to coordinate the startup and shutdown of parallel workers. Second, it synchronizes various pieces of state (e.g. GUCs, combo CID mappings, transaction snapshot) from the parallel group leader to the worker processes. Third, it prohibits various operations that would result in unsafe changes to that state while parallelism is active. Finally, it propagates events that would result in an ErrorResponse, NoticeResponse, or NotifyResponse message being sent to the client from the parallel workers back to the master, from which they can then be sent on to the client. Robert Haas, Amit Kapila, Noah Misch, Rushabh Lathia, Jeevan Chalke. Suggestions and review from Andres Freund, Heikki Linnakangas, Noah Misch, Simon Riggs, Euler Taveira, and Jim Nasby.
Diffstat (limited to 'src/backend/access/transam/xlog.c')
-rw-r--r--src/backend/access/transam/xlog.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index da7b6c2fadd..6cf441534cc 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -292,6 +292,14 @@ static TimeLineID curFileTLI;
* end+1 of the last record, and is reset when we end a top-level transaction,
* or start a new one; so it can be used to tell if the current transaction has
* created any XLOG records.
+ *
+ * While in parallel mode, this may not be fully up to date. When committing,
+ * a transaction can assume this covers all xlog records written either by the
+ * user backend or by any parallel worker which was present at any point during
+ * the transaction. But when aborting, or when still in parallel mode, other
+ * parallel backends may have written WAL records at later LSNs than the value
+ * stored here. The parallel leader advances its own copy, when necessary,
+ * in WaitForParallelWorkersToFinish.
*/
static XLogRecPtr ProcLastRecPtr = InvalidXLogRecPtr;