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Support synchronization of snapshots through an export/import procedure.

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A transaction can export a snapshot with pg_export_snapshot(), and then
others can import it with SET TRANSACTION SNAPSHOT.  The data does not
leave the server so there are not security issues.  A snapshot can only
be imported while the exporting transaction is still running, and there
are some other restrictions.

I'm not totally convinced that we've covered all the bases for SSI (true
serializable) mode, but it works fine for lesser isolation modes.

Joachim Wieland, reviewed by Marko Tiikkaja, and rather heavily modified
by Tom Lane
This commit is contained in:
Tom Lane
2011-10-22 18:22:45 -04:00
parent b436c72f61
commit bb446b689b
17 changed files with 1030 additions and 34 deletions
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13
src/backend/parser/gram.y
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@ -553,8 +553,8 @@ static void processCASbits(int cas_bits, int location, const char *constrType,
SAVEPOINT SCHEMA SCROLL SEARCH SECOND_P SECURITY SELECT SEQUENCE SEQUENCES
SERIALIZABLE SERVER SESSION SESSION_USER SET SETOF SHARE
SHOW SIMILAR SIMPLE SMALLINT SOME STABLE STANDALONE_P START STATEMENT
STATISTICS STDIN STDOUT STORAGE STRICT_P STRIP_P SUBSTRING
SHOW SIMILAR SIMPLE SMALLINT SNAPSHOT SOME STABLE STANDALONE_P START
STATEMENT STATISTICS STDIN STDOUT STORAGE STRICT_P STRIP_P SUBSTRING
SYMMETRIC SYSID SYSTEM_P
TABLE TABLES TABLESPACE TEMP TEMPLATE TEMPORARY TEXT_P THEN TIME TIMESTAMP
@ -1352,6 +1352,15 @@ set_rest: /* Generic SET syntaxes: */
n->args = list_make1(makeStringConst($3 == XMLOPTION_DOCUMENT ? "DOCUMENT" : "CONTENT", @3));
$$ = n;
}
/* Special syntaxes invented by PostgreSQL: */
| TRANSACTION SNAPSHOT Sconst
{
VariableSetStmt *n = makeNode(VariableSetStmt);
n->kind = VAR_SET_MULTI;
n->name = "TRANSACTION SNAPSHOT";
n->args = list_make1(makeStringConst($3, @3));
$$ = n;
}
;
var_name: ColId { $$ = $1; }