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Merge the various forms of transaction commit & abort records.

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Since 465883b0a two versions of commit records have existed. A compact
version that was used when no cache invalidations, smgr unlinks and
similar were needed, and a full version that could deal with all
that. Additionally the full version was embedded into twophase commit
records.

That resulted in a measurable reduction in the size of the logged WAL in
some workloads. But more recently additions like logical decoding, which
e.g. needs information about the database something was executed on,
made it applicable in fewer situations. The static split generally made
it hard to expand the commit record, because concerns over the size made
it hard to add anything to the compact version.

Additionally it's not particularly pretty to have twophase.c insert
RM_XACT records.

Rejigger things so that the commit and abort records only have one form
each, including the twophase equivalents. The presence of the various
optional (in the sense of not being in every record) pieces is indicated
by a bits in the 'xinfo' flag.  That flag previously was not included in
compact commit records. To prevent an increase in size due to its
presence, it's only included if necessary; signalled by a bit in the
xl_info bits available for xact.c, similar to heapam.c's
XLOG_HEAP_OPMASK/XLOG_HEAP_INIT_PAGE.

Twophase commit/aborts are now the same as their normal
counterparts. The original transaction's xid is included in an optional
data field.

This means that commit records generally are smaller, except in the case
of a transaction with subtransactions, but no other special cases; the
increase there is four bytes, which seems acceptable given that the more
common case of not having subtransactions shrank.  The savings are
especially measurable for twophase commits, which previously always used
the full version; but will in practice only infrequently have required
that.

The motivation for this work are not the space savings and and
deduplication though; it's that it makes it easier to extend commit
records with additional information. That's just a few lines of code
now; without impacting the common case where that information is not
needed.

Discussion: 20150220152150.GD4149@awork2.anarazel.de,
    235610.92468.qm%40web29004.mail.ird.yahoo.com

Reviewed-By: Heikki Linnakangas, Simon Riggs
This commit is contained in:
Andres Freund
2015-03-15 17:37:07 +01:00
parent a0f5954af1
commit 4f1b890b13
7 changed files with 752 additions and 511 deletions
Download Patch File Download Diff File Expand all files Collapse all files

223
src/include/access/xact.h
View File

@@ -18,6 +18,7 @@
#include "lib/stringinfo.h"
#include "nodes/pg_list.h"
#include "storage/relfilenode.h"
#include "storage/sinval.h"
#include "utils/datetime.h"
@@ -103,8 +104,8 @@ typedef void (*SubXactCallback) (SubXactEvent event, SubTransactionId mySubid,
*/
/*
* XLOG allows to store some information in high 4 bits of log
* record xl_info field
* XLOG allows to store some information in high 4 bits of log record xl_info
* field. We use 3 for the opcode, and one about an optional flag variable.
*/
#define XLOG_XACT_COMMIT 0x00
#define XLOG_XACT_PREPARE 0x10
@@ -112,7 +113,41 @@ typedef void (*SubXactCallback) (SubXactEvent event, SubTransactionId mySubid,
#define XLOG_XACT_COMMIT_PREPARED 0x30
#define XLOG_XACT_ABORT_PREPARED 0x40
#define XLOG_XACT_ASSIGNMENT 0x50
#define XLOG_XACT_COMMIT_COMPACT 0x60
/* free opcode 0x60 */
/* free opcode 0x70 */
/* mask for filtering opcodes out of xl_info */
#define XLOG_XACT_OPMASK 0x70
/* does this record have a 'xinfo' field or not */
#define XLOG_XACT_HAS_INFO 0x80
/*
* The following flags, stored in xinfo, determine which information is
* contained in commit/abort records.
*/
#define XACT_XINFO_HAS_DBINFO (1U << 0)
#define XACT_XINFO_HAS_SUBXACTS (1U << 1)
#define XACT_XINFO_HAS_RELFILENODES (1U << 2)
#define XACT_XINFO_HAS_INVALS (1U << 3)
#define XACT_XINFO_HAS_TWOPHASE (1U << 4)
/*
* Also stored in xinfo, these indicating a variety of additional actions that
* need to occur when emulating transaction effects during recovery.
*
* They are named XactCompletion... to differentiate them from
* EOXact... routines which run at the end of the original transaction
* completion.
*/
#define XACT_COMPLETION_UPDATE_RELCACHE_FILE (1U << 30)
#define XACT_COMPLETION_FORCE_SYNC_COMMIT (1U << 31)
/* Access macros for above flags */
#define XactCompletionRelcacheInitFileInval(xinfo) \
(!!(xinfo & XACT_COMPLETION_UPDATE_RELCACHE_FILE))
#define XactCompletionForceSyncCommit(xinfo) \
(!!(xinfo & XACT_COMPLETION_FORCE_SYNC_COMMIT))
typedef struct xl_xact_assignment
{
@@ -123,85 +158,130 @@ typedef struct xl_xact_assignment
#define MinSizeOfXactAssignment offsetof(xl_xact_assignment, xsub)
typedef struct xl_xact_commit_compact
{
TimestampTz xact_time; /* time of commit */
int nsubxacts; /* number of subtransaction XIDs */
/* ARRAY OF COMMITTED SUBTRANSACTION XIDs FOLLOWS */
TransactionId subxacts[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_commit_compact;
/*
* Commit and abort records can contain a lot of information. But a large
* portion of the records won't need all possible pieces of information. So we
* only include what's needed.
*
* A minimal commit/abort record only consists out of a xl_xact_commit/abort
* struct. The presence of additional information is indicated by bits set in
* 'xl_xact_xinfo->xinfo'. The presence of the xinfo field itself is signalled
* by a set XLOG_XACT_HAS_INFO bit in the xl_info field.
*
* NB: All the individual data chunks should be be sized to multiples of
* sizeof(int) and only require int32 alignment.
*/
#define MinSizeOfXactCommitCompact offsetof(xl_xact_commit_compact, subxacts)
/* sub-records for commit/abort */
typedef struct xl_xact_xinfo
{
/*
* Even though we right now only require 1 byte of space in xinfo we use
* four so following records don't have to care about alignment. Commit
* records can be large, so copying large portions isn't attractive.
*/
uint32 xinfo;
} xl_xact_xinfo;
typedef struct xl_xact_dbinfo
{
Oid dbId; /* MyDatabaseId */
Oid tsId; /* MyDatabaseTableSpace */
} xl_xact_dbinfo;
typedef struct xl_xact_subxacts
{
int nsubxacts; /* number of subtransaction XIDs */
TransactionId subxacts[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_subxacts;
#define MinSizeOfXactSubxacts offsetof(xl_xact_subxacts, subxacts)
typedef struct xl_xact_relfilenodes
{
int nrels; /* number of subtransaction XIDs */
RelFileNode xnodes[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_relfilenodes;
#define MinSizeOfXactRelfilenodes offsetof(xl_xact_relfilenodes, xnodes)
typedef struct xl_xact_invals
{
int nmsgs; /* number of shared inval msgs */
SharedInvalidationMessage msgs[FLEXIBLE_ARRAY_MEMBER];
} xl_xact_invals;
#define MinSizeOfXactInvals offsetof(xl_xact_invals, msgs)
typedef struct xl_xact_twophase
{
TransactionId xid;
} xl_xact_twophase;
#define MinSizeOfXactInvals offsetof(xl_xact_invals, msgs)
typedef struct xl_xact_commit
{
TimestampTz xact_time; /* time of commit */
uint32 xinfo; /* info flags */
int nrels; /* number of RelFileNodes */
int nsubxacts; /* number of subtransaction XIDs */
int nmsgs; /* number of shared inval msgs */
Oid dbId; /* MyDatabaseId */
Oid tsId; /* MyDatabaseTableSpace */
/* Array of RelFileNode(s) to drop at commit */
RelFileNode xnodes[FLEXIBLE_ARRAY_MEMBER];
/* ARRAY OF COMMITTED SUBTRANSACTION XIDs FOLLOWS */
/* ARRAY OF SHARED INVALIDATION MESSAGES FOLLOWS */
/* xl_xact_xinfo follows if XLOG_XACT_HAS_INFO */
/* xl_xact_dbinfo follows if XINFO_HAS_DBINFO */
/* xl_xact_subxacts follows if XINFO_HAS_SUBXACT */
/* xl_xact_relfilenodes follows if XINFO_HAS_RELFILENODES */
/* xl_xact_invals follows if XINFO_HAS_INVALS */
/* xl_xact_twophase follows if XINFO_HAS_TWOPHASE */
} xl_xact_commit;
#define MinSizeOfXactCommit offsetof(xl_xact_commit, xnodes)
/*
* These flags are set in the xinfo fields of WAL commit records,
* indicating a variety of additional actions that need to occur
* when emulating transaction effects during recovery.
* They are named XactCompletion... to differentiate them from
* EOXact... routines which run at the end of the original
* transaction completion.
*/
#define XACT_COMPLETION_UPDATE_RELCACHE_FILE 0x01
#define XACT_COMPLETION_FORCE_SYNC_COMMIT 0x02
/* Access macros for above flags */
#define XactCompletionRelcacheInitFileInval(xinfo) (xinfo & XACT_COMPLETION_UPDATE_RELCACHE_FILE)
#define XactCompletionForceSyncCommit(xinfo) (xinfo & XACT_COMPLETION_FORCE_SYNC_COMMIT)
#define MinSizeOfXactCommit (offsetof(xl_xact_commit, xact_time) + sizeof(TimestampTz))
typedef struct xl_xact_abort
{
TimestampTz xact_time; /* time of abort */
int nrels; /* number of RelFileNodes */
int nsubxacts; /* number of subtransaction XIDs */
/* Array of RelFileNode(s) to drop at abort */
RelFileNode xnodes[FLEXIBLE_ARRAY_MEMBER];
/* ARRAY OF ABORTED SUBTRANSACTION XIDs FOLLOWS */
/* xl_xact_xinfo follows if XLOG_XACT_HAS_INFO */
/* No db_info required */
/* xl_xact_subxacts follows if HAS_SUBXACT */
/* xl_xact_relfilenodes follows if HAS_RELFILENODES */
/* No invalidation messages needed. */
/* xl_xact_twophase follows if XINFO_HAS_TWOPHASE */
} xl_xact_abort;
/* Note the intentional lack of an invalidation message array c.f. commit */
#define MinSizeOfXactAbort offsetof(xl_xact_abort, xnodes)
#define MinSizeOfXactAbort sizeof(xl_xact_abort)
/*
* COMMIT_PREPARED and ABORT_PREPARED are identical to COMMIT/ABORT records
* except that we have to store the XID of the prepared transaction explicitly
* --- the XID in the record header will be invalid.
* Commit/Abort records in the above form are a bit verbose to parse, so
* there's a deconstructed versions generated by ParseCommit/AbortRecord() for
* easier consumption.
*/
typedef struct xl_xact_commit_prepared
typedef struct xl_xact_parsed_commit
{
TransactionId xid; /* XID of prepared xact */
xl_xact_commit crec; /* COMMIT record */
/* MORE DATA FOLLOWS AT END OF STRUCT */
} xl_xact_commit_prepared;
TimestampTz xact_time;
#define MinSizeOfXactCommitPrepared offsetof(xl_xact_commit_prepared, crec.xnodes)
uint32 xinfo;
typedef struct xl_xact_abort_prepared
Oid dbId; /* MyDatabaseId */
Oid tsId; /* MyDatabaseTableSpace */
int nsubxacts;
TransactionId *subxacts;
int nrels;
RelFileNode *xnodes;
int nmsgs;
SharedInvalidationMessage *msgs;
TransactionId twophase_xid; /* only for 2PC */
} xl_xact_parsed_commit;
typedef struct xl_xact_parsed_abort
{
TransactionId xid; /* XID of prepared xact */
xl_xact_abort arec; /* ABORT record */
/* MORE DATA FOLLOWS AT END OF STRUCT */
} xl_xact_abort_prepared;
TimestampTz xact_time;
uint32 xinfo;
#define MinSizeOfXactAbortPrepared offsetof(xl_xact_abort_prepared, arec.xnodes)
int nsubxacts;
TransactionId *subxacts;
int nrels;
RelFileNode *xnodes;
TransactionId twophase_xid; /* only for 2PC */
} xl_xact_parsed_abort;
/* ----------------
@@ -256,8 +336,25 @@ extern void UnregisterSubXactCallback(SubXactCallback callback, void *arg);
extern int xactGetCommittedChildren(TransactionId **ptr);
extern XLogRecPtr XactLogCommitRecord(TimestampTz commit_time,
int nsubxacts, TransactionId *subxacts,
int nrels, RelFileNode *rels,
int nmsgs, SharedInvalidationMessage *msgs,
bool relcacheInval, bool forceSync,
TransactionId twophase_xid);
extern XLogRecPtr XactLogAbortRecord(TimestampTz abort_time,
int nsubxacts, TransactionId *subxacts,
int nrels, RelFileNode *rels,
TransactionId twophase_xid);
extern void xact_redo(XLogReaderState *record);
/* xactdesc.c */
extern void xact_desc(StringInfo buf, XLogReaderState *record);
extern const char *xact_identify(uint8 info);
/* also in xactdesc.c, so they can be shared between front/backend code */
extern void ParseCommitRecord(uint8 info, xl_xact_commit *xlrec, xl_xact_parsed_commit *parsed);
extern void ParseAbortRecord(uint8 info, xl_xact_abort *xlrec, xl_xact_parsed_abort *parsed);
#endif /* XACT_H */