farrokhi/pg_repack
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Add comment explaining how race condition between CREATE TABLE ... AS SELECT and recording of log entries is avoided.

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Josh Kupershmidt 2012-11-29 20:27:33 -07:00
parent d402a73e42
commit 3b856623fd
1 changed files with 10 additions and 0 deletions
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10
bin/pg_repack.c
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@ -507,6 +507,10 @@ repack_one_table(const repack_table *table, const char *orderby)
*/ */
elog(DEBUG2, "---- copy tuples ----"); elog(DEBUG2, "---- copy tuples ----");
/* Must use SERIALIZABLE (or at least not READ COMMITTED) to avoid race
* condition between the create_table statement and rows subsequently
* being added to the log.
*/
command("BEGIN ISOLATION LEVEL SERIALIZABLE", 0, NULL); command("BEGIN ISOLATION LEVEL SERIALIZABLE", 0, NULL);
/* SET work_mem = maintenance_work_mem */ /* SET work_mem = maintenance_work_mem */
command("SELECT set_config('work_mem', current_setting('maintenance_work_mem'), true)", 0, NULL); command("SELECT set_config('work_mem', current_setting('maintenance_work_mem'), true)", 0, NULL);
@ -515,6 +519,12 @@ repack_one_table(const repack_table *table, const char *orderby)
res = execute(SQL_XID_SNAPSHOT, 0, NULL); res = execute(SQL_XID_SNAPSHOT, 0, NULL);
vxid = strdup(PQgetvalue(res, 0, 0)); vxid = strdup(PQgetvalue(res, 0, 0));
PQclear(res); PQclear(res);
/* Delete any existing entries in the log table now, since we have not
* yet run the CREATE TABLE ... AS SELECT, which will take in all existing
* rows from the target table; if we also included prior rows from the
* log we could wind up with duplicates.
*/
command(table->delete_log, 0, NULL); command(table->delete_log, 0, NULL);
command(table->create_table, 0, NULL); command(table->create_table, 0, NULL);
printfStringInfo(&sql, "SELECT repack.disable_autovacuum('repack.table_%u')", table->target_oid); printfStringInfo(&sql, "SELECT repack.disable_autovacuum('repack.table_%u')", table->target_oid);