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Subject: [PATCH v4 6/8] Move removal of old logical rewrite mapping files to custodian.
Date: Sun, 12 Dec 2021 22:07:11 -0800
If there are many such files to remove, checkpoints can take much
longer. To avoid this, move this work to the newly-introduced
custodian process.
---
src/backend/access/heap/rewriteheap.c | 83 +++++++++++++++++++++++----
src/backend/postmaster/checkpointer.c | 33 +++++++++++
src/backend/postmaster/custodian.c | 10 ++++
src/include/access/rewriteheap.h | 1 +
src/include/postmaster/bgwriter.h | 3 +
5 files changed, 120 insertions(+), 10 deletions(-)
diff --git a/src/backend/access/heap/rewriteheap.c b/src/backend/access/heap/rewriteheap.c
index 2a53826736..c5a1103687 100644
--- a/src/backend/access/heap/rewriteheap.c
+++ b/src/backend/access/heap/rewriteheap.c
@@ -116,10 +116,13 @@
#include "lib/ilist.h"
#include "miscadmin.h"
#include "pgstat.h"
+#include "postmaster/bgwriter.h"
+#include "postmaster/interrupt.h"
#include "replication/logical.h"
#include "replication/slot.h"
#include "storage/bufmgr.h"
#include "storage/fd.h"
+#include "storage/proc.h"
#include "storage/procarray.h"
#include "storage/smgr.h"
#include "utils/memutils.h"
@@ -1182,7 +1185,8 @@ heap_xlog_logical_rewrite(XLogReaderState *r)
* Perform a checkpoint for logical rewrite mappings
*
* This serves two tasks:
- * 1) Remove all mappings not needed anymore based on the logical restart LSN
+ * 1) Alert the custodian to remove all mappings not needed anymore based on the
+ * logical restart LSN
* 2) Flush all remaining mappings to disk, so that replay after a checkpoint
* only has to deal with the parts of a mapping that have been written out
* after the checkpoint started.
@@ -1210,6 +1214,11 @@ CheckPointLogicalRewriteHeap(void)
if (cutoff != InvalidXLogRecPtr && redo < cutoff)
cutoff = redo;
+ /* let the custodian know what it can remove */
+ CheckPointSetLogicalRewriteCutoff(cutoff);
+ if (ProcGlobal->custodianLatch)
+ SetLatch(ProcGlobal->custodianLatch);
+
mappings_dir = AllocateDir("pg_logical/mappings");
while ((mapping_de = ReadDir(mappings_dir, "pg_logical/mappings")) != NULL)
{
@@ -1240,15 +1249,7 @@ CheckPointLogicalRewriteHeap(void)
lsn = ((uint64) hi) << 32 | lo;
- if (lsn < cutoff || cutoff == InvalidXLogRecPtr)
- {
- elog(DEBUG1, "removing logical rewrite file \"%s\"", path);
- if (unlink(path) < 0)
- ereport(ERROR,
- (errcode_for_file_access(),
- errmsg("could not remove file \"%s\": %m", path)));
- }
- else
+ if (lsn >= cutoff && cutoff != InvalidXLogRecPtr)
{
/* on some operating systems fsyncing a file requires O_RDWR */
int fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
@@ -1286,3 +1287,65 @@ CheckPointLogicalRewriteHeap(void)
/* persist directory entries to disk */
fsync_fname("pg_logical/mappings", true);
}
+
+/*
+ * Remove all mappings not needed anymore based on the logical restart LSN saved
+ * by the checkpointer. We use this saved value instead of calling
+ * ReplicationSlotsComputeLogicalRestartLSN() so that we don't interfere with an
+ * ongoing call to CheckPointLogicalRewriteHeap() that is flushing mappings to
+ * disk.
+ */
+void
+RemoveOldLogicalRewriteMappings(void)
+{
+ XLogRecPtr cutoff;
+ DIR *mappings_dir;
+ struct dirent *mapping_de;
+ char path[MAXPGPATH + 20];
+ bool value_set = false;
+
+ cutoff = CheckPointGetLogicalRewriteCutoff(&value_set);
+ if (!value_set)
+ return;
+
+ mappings_dir = AllocateDir("pg_logical/mappings");
+ while (!ShutdownRequestPending &&
+ (mapping_de = ReadDir(mappings_dir, "pg_logical/mappings")) != NULL)
+ {
+ struct stat statbuf;
+ Oid dboid;
+ Oid relid;
+ XLogRecPtr lsn;
+ TransactionId rewrite_xid;
+ TransactionId create_xid;
+ uint32 hi,
+ lo;
+
+ if (strcmp(mapping_de->d_name, ".") == 0 ||
+ strcmp(mapping_de->d_name, "..") == 0)
+ continue;
+
+ snprintf(path, sizeof(path), "pg_logical/mappings/%s", mapping_de->d_name);
+ if (lstat(path, &statbuf) == 0 && !S_ISREG(statbuf.st_mode))
+ continue;
+
+ /* Skip over files that cannot be ours. */
+ if (strncmp(mapping_de->d_name, "map-", 4) != 0)
+ continue;
+
+ if (sscanf(mapping_de->d_name, LOGICAL_REWRITE_FORMAT,
+ &dboid, &relid, &hi, &lo, &rewrite_xid, &create_xid) != 6)
+ elog(ERROR, "could not parse filename \"%s\"", mapping_de->d_name);
+
+ lsn = ((uint64) hi) << 32 | lo;
+ if (lsn >= cutoff && cutoff != InvalidXLogRecPtr)
+ continue;
+
+ elog(DEBUG1, "removing logical rewrite file \"%s\"", path);
+ if (unlink(path) < 0)
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("could not remove file \"%s\": %m", path)));
+ }
+ FreeDir(mappings_dir);
+}
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 23f691cd47..fe0934e5a6 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -127,6 +127,9 @@ typedef struct
uint32 num_backend_writes; /* counts user backend buffer writes */
uint32 num_backend_fsync; /* counts user backend fsync calls */
+ XLogRecPtr logical_rewrite_mappings_cutoff; /* can remove older mappings */
+ bool logical_rewrite_mappings_cutoff_set;
+
int num_requests; /* current # of requests */
int max_requests; /* allocated array size */
CheckpointerRequest requests[FLEXIBLE_ARRAY_MEMBER];
@@ -1341,3 +1344,33 @@ FirstCallSinceLastCheckpoint(void)
return FirstCall;
}
+
+/*
+ * Used by CheckPointLogicalRewriteHeap() to tell the custodian which logical
+ * rewrite mapping files it can remove.
+ */
+void
+CheckPointSetLogicalRewriteCutoff(XLogRecPtr cutoff)
+{
+ SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
+ CheckpointerShmem->logical_rewrite_mappings_cutoff = cutoff;
+ CheckpointerShmem->logical_rewrite_mappings_cutoff_set = true;
+ SpinLockRelease(&CheckpointerShmem->ckpt_lck);
+}
+
+/*
+ * Used by the custodian to determine which logical rewrite mapping files it can
+ * remove.
+ */
+XLogRecPtr
+CheckPointGetLogicalRewriteCutoff(bool *value_set)
+{
+ XLogRecPtr cutoff;
+
+ SpinLockAcquire(&CheckpointerShmem->ckpt_lck);
+ cutoff = CheckpointerShmem->logical_rewrite_mappings_cutoff;
+ *value_set = CheckpointerShmem->logical_rewrite_mappings_cutoff_set;
+ SpinLockRelease(&CheckpointerShmem->ckpt_lck);
+
+ return cutoff;
+}
diff --git a/src/backend/postmaster/custodian.c b/src/backend/postmaster/custodian.c
index 0f4dbdd669..9c5479b5cf 100644
--- a/src/backend/postmaster/custodian.c
+++ b/src/backend/postmaster/custodian.c
@@ -36,6 +36,7 @@
#include <time.h>
+#include "access/rewriteheap.h"
#include "libpq/pqsignal.h"
#include "pgstat.h"
#include "postmaster/custodian.h"
@@ -218,6 +219,15 @@ CustodianMain(void)
*/
RemoveOldSerializedSnapshots();
+ /*
+ * Remove logical rewrite mapping files that are no longer needed.
+ *
+ * It is not important for these to be removed in single-user mode, so
+ * we don't need any extra handling outside of the custodian process for
+ * this.
+ */
+ RemoveOldLogicalRewriteMappings();
+
/* Calculate how long to sleep */
end_time = (pg_time_t) time(NULL);
elapsed_secs = end_time - start_time;
diff --git a/src/include/access/rewriteheap.h b/src/include/access/rewriteheap.h
index aa5c48f219..f493094557 100644
--- a/src/include/access/rewriteheap.h
+++ b/src/include/access/rewriteheap.h
@@ -53,5 +53,6 @@ typedef struct LogicalRewriteMappingData
*/
#define LOGICAL_REWRITE_FORMAT "map-%x-%x-%X_%X-%x-%x"
void CheckPointLogicalRewriteHeap(void);
+void RemoveOldLogicalRewriteMappings(void);
#endif /* REWRITE_HEAP_H */
diff --git a/src/include/postmaster/bgwriter.h b/src/include/postmaster/bgwriter.h
index 2882efd67b..051e6732cb 100644
--- a/src/include/postmaster/bgwriter.h
+++ b/src/include/postmaster/bgwriter.h
@@ -42,4 +42,7 @@ extern void CheckpointerShmemInit(void);
extern bool FirstCallSinceLastCheckpoint(void);
+extern void CheckPointSetLogicalRewriteCutoff(XLogRecPtr cutoff);
+extern XLogRecPtr CheckPointGetLogicalRewriteCutoff(bool *value_set);
+
#endif /* _BGWRITER_H */
--
2.25.1
--BXVAT5kNtrzKuDFl
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment;
filename="v4-0007-Use-syncfs-in-CheckPointLogicalRewriteHeap-for-sh.patch"
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