From f05f5f20a468efa82d13a99687ac5d3a5d80a3c9 Mon Sep 17 00:00:00 2001
From: tbordaz <tbordaz@redhat.com>
Date: Tue, 23 Feb 2021 13:42:31 +0100
Subject: [PATCH] Issue 4644 - Large updates can reset the CLcache to the
beginning of the changelog (#4647)
Bug description:
The replication agreements are using bulk load to load updates.
For bulk load it uses a cursor with DB_MULTIPLE_KEY and DB_NEXT.
Before using the cursor, it must be initialized with DB_SET.
If during the cursor/DB_SET the CSN refers to an update that is larger than
the size of the provided buffer, then the cursor remains not initialized and
c_get returns DB_BUFFER_SMALL.
The consequence is that the next c_get(DB_MULTIPLE_KEY and DB_NEXT) will return the
first record in the changelog DB. This break CLcache.
Fix description:
The fix is to harden cursor initialization so that if DB_SET fails
because of DB_BUFFER_SMALL. It reallocates buf_data and retries a DB_SET.
If DB_SET can not be initialized it logs a warning.
The patch also changes the behaviour of the fix #4492.
#4492 detected a massive (1day) jump prior the starting csn and ended the
replication session. If the jump was systematic, for example
if the CLcache got broken because of a too large updates, then
replication was systematically stopped.
This patch suppress the systematically stop, letting RA doing a big jump.
From #4492 only remains the warning.
relates: https://github.com/389ds/389-ds-base/issues/4644
Reviewed by: Pierre Rogier (Thanks !!!!)
Platforms tested: F31
---
.../servers/plugins/replication/cl5_clcache.c | 68 +++++++++++++++----
1 file changed, 53 insertions(+), 15 deletions(-)
diff --git a/ldap/servers/plugins/replication/cl5_clcache.c b/ldap/servers/plugins/replication/cl5_clcache.c
index fcbca047a..90dec4d54 100644
--- a/ldap/servers/plugins/replication/cl5_clcache.c
+++ b/ldap/servers/plugins/replication/cl5_clcache.c
@@ -370,9 +370,7 @@ clcache_load_buffer(CLC_Buffer *buf, CSN **anchorCSN, int *continue_on_miss, cha
}
csn_as_string(buf->buf_current_csn, 0, curr);
slapi_log_err(loglevel, buf->buf_agmt_name,
- "clcache_load_buffer - bulk load cursor (%s) is lower than starting csn %s. Ending session.\n", curr, initial_starting_csn);
- /* it just end the session with UPDATE_NO_MORE_UPDATES */
- rc = CLC_STATE_DONE;
+ "clcache_load_buffer - bulk load cursor (%s) is lower than starting csn %s.\n", curr, initial_starting_csn);
}
}
@@ -413,10 +411,7 @@ clcache_load_buffer(CLC_Buffer *buf, CSN **anchorCSN, int *continue_on_miss, cha
}
csn_as_string(buf->buf_current_csn, 0, curr);
slapi_log_err(loglevel, buf->buf_agmt_name,
- "clcache_load_buffer - (DB_SET_RANGE) bulk load cursor (%s) is lower than starting csn %s. Ending session.\n", curr, initial_starting_csn);
- rc = DB_NOTFOUND;
-
- return rc;
+ "clcache_load_buffer - (DB_SET_RANGE) bulk load cursor (%s) is lower than starting csn %s.\n", curr, initial_starting_csn);
}
}
}
@@ -444,6 +439,42 @@ clcache_load_buffer(CLC_Buffer *buf, CSN **anchorCSN, int *continue_on_miss, cha
return rc;
}
+/* Set a cursor to a specific key (buf->buf_key)
+ * In case buf_data is too small to receive the value, DB_SET fails
+ * (DB_BUFFER_SMALL). This let the cursor uninitialized that is
+ * problematic because further cursor DB_NEXT will reset the cursor
+ * to the beginning of the CL.
+ * If buf_data is too small, this function reallocates enough space
+ *
+ * It returns the return code of cursor->c_get
+ */
+static int
+clcache_cursor_set(DBC *cursor, CLC_Buffer *buf)
+{
+ int rc;
+ uint32_t ulen;
+ uint32_t dlen;
+ uint32_t size;
+
+ rc = cursor->c_get(cursor, &buf->buf_key, &buf->buf_data, DB_SET);
+ if (rc == DB_BUFFER_SMALL) {
+ uint32_t ulen;
+
+ /* Fortunately, buf->buf_data.size has been set by
+ * c_get() to the actual data size needed. So we can
+ * reallocate the data buffer and try to set again.
+ */
+ ulen = buf->buf_data.ulen;
+ buf->buf_data.ulen = (buf->buf_data.size / DEFAULT_CLC_BUFFER_PAGE_SIZE + 1) * DEFAULT_CLC_BUFFER_PAGE_SIZE;
+ buf->buf_data.data = slapi_ch_realloc(buf->buf_data.data, buf->buf_data.ulen);
+ slapi_log_err(SLAPI_LOG_REPL, buf->buf_agmt_name,
+ "clcache_cursor_set - buf data len reallocated %d -> %d bytes (DB_BUFFER_SMALL)\n",
+ ulen, buf->buf_data.ulen);
+ rc = cursor->c_get(cursor, &buf->buf_key, &buf->buf_data, DB_SET);
+ }
+ return rc;
+}
+
static int
clcache_load_buffer_bulk(CLC_Buffer *buf, int flag)
{
@@ -478,17 +509,24 @@ retry:
if (use_flag == DB_NEXT) {
/* For bulk read, position the cursor before read the next block */
- rc = cursor->c_get(cursor,
- &buf->buf_key,
- &buf->buf_data,
- DB_SET);
+ rc = clcache_cursor_set(cursor, buf);
}
- /*
- * Continue if the error is no-mem since we don't need to
- * load in the key record anyway with DB_SET.
- */
if (0 == rc || DB_BUFFER_SMALL == rc) {
+ /*
+ * It should not have failed with DB_BUFFER_SMALL as we tried
+ * to adjust buf_data in clcache_cursor_set.
+ * But if it failed with DB_BUFFER_SMALL, there is a risk in clcache_cursor_get
+ * that the cursor will be reset to the beginning of the changelog.
+ * Returning an error at this point will stop replication that is
+ * a risk. So just accept the risk of a reset to the beginning of the CL
+ * and log an alarming message.
+ */
+ if (rc == DB_BUFFER_SMALL) {
+ slapi_log_err(SLAPI_LOG_WARNING, buf->buf_agmt_name,
+ "clcache_load_buffer_bulk - Fail to position on csn=%s from the changelog (too large update ?). Risk of full CL evaluation.\n",
+ (char *)buf->buf_key.data);
+ }
rc = clcache_cursor_get(cursor, buf, use_flag);
}
}
--
2.31.1