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Add option to control snapshot export to CREATE_REPLICATION_SLOT

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We used to export snapshots unconditionally in CREATE_REPLICATION_SLOT
in the replication protocol, but several upcoming patches want more
control over what happens.

Suppress snapshot export in pg_recvlogical, which neither needs nor can
use the exported snapshot.  Since snapshot exporting can fail this
improves reliability.

This also paves the way for allowing the creation of replication slots
on standbys, which cannot export snapshots because they cannot allocate
new XIDs.

Author: Petr Jelinek <petr.jelinek@2ndquadrant.com>
This commit is contained in:
Peter Eisentraut
2017-03-14 17:13:56 -04:00
parent 7150402655
commit eb4da3e380
10 changed files with 141 additions and 26 deletions
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58
src/backend/replication/walsender.c
View File

@@ -51,6 +51,7 @@
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
#include "commands/defrem.h"
#include "funcapi.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
@@ -737,6 +738,48 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
return count;
}
/*
* Process extra options given to CREATE_REPLICATION_SLOT.
*/
static void
parseCreateReplSlotOptions(CreateReplicationSlotCmd *cmd,
bool *reserve_wal,
bool *export_snapshot)
{
ListCell *lc;
bool snapshot_action_given = false;
bool reserve_wal_given = false;
/* Parse options */
foreach (lc, cmd->options)
{
DefElem *defel = (DefElem *) lfirst(lc);
if (strcmp(defel->defname, "export_snapshot") == 0)
{
if (snapshot_action_given || cmd->kind != REPLICATION_KIND_LOGICAL)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("conflicting or redundant options")));
snapshot_action_given = true;
*export_snapshot = defGetBoolean(defel);
}
else if (strcmp(defel->defname, "reserve_wal") == 0)
{
if (reserve_wal_given || cmd->kind != REPLICATION_KIND_PHYSICAL)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("conflicting or redundant options")));
reserve_wal_given = true;
*reserve_wal = true;
}
else
elog(ERROR, "unrecognized option: %s", defel->defname);
}
}
/*
* Create a new replication slot.
*/
@@ -746,6 +789,8 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
const char *snapshot_name = NULL;
char xpos[MAXFNAMELEN];
char *slot_name;
bool reserve_wal = false;
bool export_snapshot = true;
DestReceiver *dest;
TupOutputState *tstate;
TupleDesc tupdesc;
@@ -754,6 +799,8 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
Assert(!MyReplicationSlot);
parseCreateReplSlotOptions(cmd, &reserve_wal, &export_snapshot);
/* setup state for XLogReadPage */
sendTimeLineIsHistoric = false;
sendTimeLine = ThisTimeLineID;
@@ -799,10 +846,13 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
DecodingContextFindStartpoint(ctx);
/*
* Export a plain (not of the snapbuild.c type) snapshot to the user
* that can be imported into another session.
* Export the snapshot if we've been asked to do so.
*
* NB. We will convert the snapbuild.c kind of snapshot to normal
* snapshot when doing this.
*/
snapshot_name = SnapBuildExportSnapshot(ctx->snapshot_builder);
if (export_snapshot)
snapshot_name = SnapBuildExportSnapshot(ctx->snapshot_builder);
/* don't need the decoding context anymore */
FreeDecodingContext(ctx);
@@ -810,7 +860,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
if (!cmd->temporary)
ReplicationSlotPersist();
}
else if (cmd->kind == REPLICATION_KIND_PHYSICAL && cmd->reserve_wal)
else if (cmd->kind == REPLICATION_KIND_PHYSICAL && reserve_wal)
{
ReplicationSlotReserveWal();