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Type:
Improvement
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Resolution: Unresolved
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: Checkpoints
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StorEng - Defined Pipeline
Currently, we allow any session to read a checkpoint at anytime. However, the cost is that we have to do the setups and checks for every cursor call with the code:
#define WT_WITH_CHECKPOINT(session, cbt, op) \
do { \
WT_TXN *__saved_txn; \
uint64_t __saved_write_gen = (session)->checkpoint_write_gen; \
\
if ((cbt)->checkpoint_txn != NULL) { \
__saved_txn = (session)->txn; \
if (F_ISSET(__saved_txn, WT_TXN_IS_CHECKPOINT)) { \
WT_ASSERT( \
session, (cbt)->checkpoint_write_gen == (session)->checkpoint_write_gen); \
__saved_txn = NULL; \
} else { \
(session)->txn = (cbt)->checkpoint_txn; \
if ((cbt)->checkpoint_hs_dhandle != NULL) { \
WT_ASSERT(session, (session)->hs_checkpoint == NULL); \
(session)->hs_checkpoint = (cbt)->checkpoint_hs_dhandle->checkpoint; \
} \
__saved_write_gen = (session)->checkpoint_write_gen; \
(session)->checkpoint_write_gen = (cbt)->checkpoint_write_gen; \
} \
} else \
__saved_txn = NULL; \
op; \
if (__saved_txn != NULL) { \
(session)->txn = __saved_txn; \
(session)->hs_checkpoint = NULL; \
(session)->checkpoint_write_gen = __saved_write_gen; \
} \
} while (0)
I don't see the reason why we cannot have a dedicated session to read the checkpoint. In this way, we can do this setup at the session level and remove this code for each cursor operation. This should speed up both the checkpoint read and normal transaction operations.